I believe that regulator output has touched the heat sink which is directly connected to the collector of the big transistor which caused that Cap to blow
I'm surprised Sorin missed that. I see that a plastic insulator magically appeared under the replacement. I was waiting for the increasingly hot rheostat to be dropped onto the power supply.
I built that kit in 2019 - building it into a housing and added 10 turn pots and a Volt/amp meter. And it works great !! Best thing ...... unlike many of the constant current power modules you can buy - this one actually does a great job with current limiting !! It actually limits current down to 2.5 mA. Great for power injection and testing diodes !!
Same. I killed the first opamp from the output side with arking a street light ballast inductor. Perfect supply for the price. The input AC voltage is critical: the opamps use the full voltage rail with the -5V.
12:40 if you go frame by frame first you see big spark that looks like it comes from transistor and then smoke + red glow from the capacitor on voltage regulator for the fan. I think that regulator touched fan pipe and capacitor on fan regulator shorted over the transistor 😎. FYI when you pause the video you can move forward and backwards frame by frame by comma and dot keys on the keyboard 🙂.
Gotta love the fact that your videos are so "organic". You also include fails along so we can learn from that, coming to a conclusion in the end and learning a new fix or a new way to blow up electronics, haha. Keep it up, Sorin! Looking forward to the next upload. Have a nice evening
beware!!! :D that kit is wellknown, and have some flawless, too. the most easier flaw to fix is using for AO's a local power supply, like a Zenner and a resistor, calculated for no more than 30V over AO's, negative power included! it's a -5V on negative, so, 30-5=25, but there are no 25 V Zenners, not 3 terminal stabs, so, 24 volts. most easier is to use the already present 24V, for cooler. some small adjustment for resistors, and is perfect. of course, you need a nicely strong mains trafo, 24V or a bit more. or a bit less, if you accept a bit smaller voltage on full load... :) (written immediately after i seen the kit... is a wellknown for me! :D now, play to the finish... i'm really curious what you will find about... as a side note, is a really antique schematic, older than 60 years, in some variants. one of them use 3/4 AO's in a 324, and the last one is used as overload indicator, doubled as relay activator... :P ) later: min 13: to much current on a diode in the bridge! it's what happens most of time, without dealing with small smps's :D also, looks like you don't set the 0 volts, that blue multiturn is used to set the 0 volts, because this is a "virtual ground" power supply. for same reason you fried it first time with a 19 v laptop brick! :) lemme see... you just repeated the very same mistakes me and a lot of people does for the first time they meet this schematic, and, later, this kit... chinese started to manufacture and sell those kits some 15-18 years ago! :) i patiently seen the video to the final... Sorin, that blue led is NOT "power on" led, but "overload led", it need to be on only when you load the PS with more than your current limit! :) why is all the time on? some of these kits are correct, some not... some have a slight different schematic than the original in that part, and led is on the opposite directions, and is on all the time. other kits have wrong orientation printed on pcb. looks like electronics-diy point com shunned out that power supply, even this was their top-grade reason to check their website, a lot of years... you can find a lot with a google search, but i have trust in "radioscamateurs" sites, so... check the link down. i have not patience to search exactly about setting-up procedure, i had done it for some kits, and leaved it alone... also, with a bit of more searching, you can find a giga-talk about that schematic on a romanian forum, in power supplies section. a forum i leaved it for some years, even if i was one of the only posters there, for a lot of years, too... :) să fii iubit. :) www.qsl.net/z33t/dc_0-30v_0-3A_eng.html
As built the transistors are passing 5+ Amps (100+ Watts), but they are not dissipating anything near to that, which is why the fan/heatsink are coping and the transistors remain fairly cool. If you hooked up a 35V transformer as you suggested, then particularly when used at lower voltages the transistors will be dissipating much more power and thus get hotter, to the extent that you'll probably need a bigger fan/heatsink combination. Which is why many power supplies switch transformer windings in and out dependant on the voltage required at the output.
Learning by doing is the best way to lean and to achieve experience and not be afraid of the unknown or new. Smoke is good, smoking lessons from Sorin are funny, familiar friendly and very infesting always. All the best “moșu!”. Big hug!Cosmin from Switzerland 🇨🇭!
I noticed that your current limit led is constantly on, it should only come on when the current limiting kicks in. On my board the silkscreen had a error and the transistor that controls the led needs to be rotated 180 degrees that will make the led work correctly.
I originally posted something like this in response to someone's question, but it seems a lot of people miss the issue, so I'm posting again with some elaboration. This is intended for use as a bench power supply. With a bench supply you really need to be able to deliver full rated current into a short circuit or close to a short. You may not need to do this often, but the need does arise. Your power supply needs to be able to survive it. When the output current is set to maximum and the output is shorted, the power dissipation in the transistors will actually be more than 100% of the full rated output power of the supply. If the supply is rated for 5 A and 30 V, that means the transistors would dissipate 150 watts, *minimum.* If fact the dissipation will be even greater because the voltage across the transistors will be equal to the full unregulated voltage from the bridge rectifier and filter capacitor. For the 30 volt supply that might be 35 volts (or more). At 35 volts the transistors would dissipate 175 watts at 5 A. That is a lot of heat to get rid of! If you use the regulator for some specific application where the output voltage is not very low, the situation is different. With high powers it is important to be careful that the transistors used have adequate safe operating area. "Second breakdown" can limit the allowable steady-state power dissipation to something well below the nominal rating of the device. With low voltage this often isn't a problem, but it very definitely becomes a problem when you get up into tens of volts.
i built two of the power supplies powered up and op amps burned up so i change op-amp to lm741 because higher voltage rail and use dip sockets. i also also use 2n3055 as output transistor. used if for five years now
Nice! I build several working great though...but take care and replace IC with good ones, I'm using TL701 instead ''originals'', also I replaced R7 with 3x1ohm/5W in parallel , gives like 0.33 and let more current flow too.
did it ever work with the original op amps at all? Mine never worked with the originals, nor with the replacements I used (not a FET op amp, but no difference in behaviour)
@@AnnaVannieuwenhuyse my worked fine with originals but I somewhere read that they're very sensitive to overvoltage so I probly order replacement at same time. But PSU end up lost in mail for half a year so I in the end never really used it, just assembled and tested.
Fantastic, Sorin. My linear power supply i made with atx desktop power supply, using - cable blue -12v and yellow cable + 12v with aliexpress regulator 2956. -12v with +12v i have + 24v alright? Also, have a generic aliexpress meter voltage/current (als288 maybe) conected in serial mode with out - and out + . I am using 1 year no problem, but, i recomend using diodo retificator 4amp in +12 (its possible calibrate diference 0.7 volts on meter adjust) Its my homenade power supply setup; DIY Ever!
13:35 - Strange thing you didnt stop video recording and check what sparked. Its power supply for fan, little capacitor. 12:39 spark. I believe that green pcb touched heatsink, and heatsink is soldered to the back of that big transistor. 18:29 you placed isolation tape on back :D
Definitely enjoyed this one, Sorin. One of your best. Please do more like this. It was funny with the flashback to the original barbecue video/livestream, too!
I went thru this adventure a couple of years ago and I was unlucky at first. Transistor blew up almost instantly at 2 amps. Later I got scammed with fake Toshiba transistors on amazon. Ended up using a 13007 extracted from an old ATX psu and problem was solved. If you have a proper power transistor with proper heatsinking, the thing does it's job. Have in mind that with this circuit, if it overheats and shorts, it will send the full unregulated power to whatever you have connected at the output.
@@spimfurt I don't know of any specific mod for that right now, I haven't done my research online. But it is actually a project I have been really wanting to make. I think by using a comparator IC we could make some kind of overvoltage protection that triggers a relay if it goes much higher than the voltage set.
The voltage on the output rectifier and capacitor filter is 24*sqrt(2) = above max rating of 7812 And seems small switching regulator short to the heatsink
Nice video! Just one comment, you said the heatsink/transistors need to dissipate 100watts. But I guess most of the 100 watts gets lost as heat in your resistive load. You could measure it.
Why measure anything when he had all numbers in from of him on that little screen? Almost 20Vx5A=100W. But yes, in a resistor, transistors only dissipate difference between input and output voltage (xA of course) so around 25W with that transformer
With this sort of supply you need transistors and heatsinking adequate to handle the full rated output current with the output short circuited, or nearly shorted. That means that probably something in the range 120 to 150% of the rated normal maximum output power is dissipated in the transistors (the dissipation is the product of the output current and the *unregulated* voltage ahead of the transistors - i.e. on the main filter capacitor).
on hight currents and low voltages, the powersupply is capable of one, but loud, click. but for real, that blue led goes off, when the short is present.
Hi Sorin, is current limiting functional? That diode on the pcb should light up only when overloaded. I have made a double stabilized source from these modules. And I had to replace all the ICs on both. And many other changes besides. Try to short-circuit the source, with a set current of 3A, and then you will see what the temperature will be on the transistors. :)
Would love to see an updated version video with all the mods you suggested a case and some testing done to it using your oscilloscope on the output for example. Plus if any more mods you can think of... Thanks for sharing though!!
i bought this a year ago. the achiles heel here is the low voltage and high current. a 3V motor powered by 1.4V and 0.8 - 1.5A for an hour caused the failure of the big transistor. the loud one. sorin, i will appreciate if you can find a way to make this power source to sustain 0.8V and 3A forewer. typicaly for ram/cpu power testing. for cooling i used the 775 heatsink from intel quad core cpu. no fan. transformers are available in some cheap speakers with amplifier. usually 2.5A, -11 and +11V = 22V. or this expensive sorins fancy toroid.
Quite hard but not impossible. In the situation you mention It Will dissipate more than 60w in heat. You Just use a bigger transistor and Active cooling
Salut Sorin. eu am facut aceasta sursa de alimentare si tot mi se ardea OP-ampurile si nu stiam de ce. eu am cumparat un traf toroidal de 24v AC dar in gol scotea 27V. traful trebuie sa scoata fix 24 V in gol ca sa nu arda integratele. 24V AC inmultit cu constanta capacitiva de 1.4 dupa redresare si filtrare o sa ai in jur de 33.6V maxim. cu 27V in gol inmultit cu 1.4 ne da 37.8V care ard integratele pentru ca nu sunt proiectate pentru o astfel de tensiune. tensiunea maxima admisa pentru TL081 este de 30V DC. ce este peste le arde si nu stiti de ce sursele nu functioneaza. pentru integrate folositi un soclu si a-ti scapat de problema cand ele se ard. frumoase videoclipuri Sorine. Ma bucur ca avem asa romani priceputi si peste hotare. o zi faina!
how about a hybrid powersupply? there the final regulation is done by a transistor operating in its linear region - but a switching mosfet pre regulator - that tracks the voltage to say - 3volts higher than the transistor to make the power that the transistor has to turn into heat that much less?
That can work quite well though dynamic performance may not be as good as with an all-linear design. You still need pass transistors rated for the maximum input voltage so that if the load is abruptly removed after running at full voltage (meaning the switcher is putting out its max voltage) the transient input-output differential across the pass device won't kill it. If the load is very abruptly increased it may take the switcher a bit of time to "catch up." With modern designs running at quite high frequency and carefully done for good dynamic performance this may not be an issue. I have watched quite a few videos of amateurs making power supplies. So far not a single one has done anything at all to test dynamic performance. Poor dynamics can lead to voltage drops which can cause circuit misoperation but usually aren't disastrous, or overshoots that can destroy circuitry being powered. Everybody just connects a meter and calls everthing good if the meter looks stable. Well, the typical DVM will show you 25 volts for a 5 kHz 100 V rectangular waveform with 25% duty cycle, so ...
I built one of these kits, but haven't had a chance to even check if it works, as I don't have a suitable transformer. it was an entertaining enough project, and maybe I'll find a decent 24v transformer in something at some point in the future to test it out.
I still have this kit somewhere assembled, ending up never using it but is there as backup, just in case. I got it for free because it was lost in mail somewhere so aliexpress give me refund, package arrive 6 months after that. btw fan will have much more problem with lower voltage, with 19V transistors don't need to drop too much but if you lower your voltage to lets say 1V and try to push 5A for long time that little heatsink would have hard time :)
Mulțumesc, Sorin. I wasn't sure how I was supposed to connect the Ammeter to the supply. My attempt resulted in the D882 transistor shorting out because I tried powering the meters from the fan output. Tried your method and it works flawlessly!
hi Sorin, I'm using this circuit since 6 yrs. lately D882 get burnt, I replace it but agian burnt, I found the cap 0.22u next to D882 damaged I replaced with used one works for a while but again D882 get burn i remove the cap and it worked fine till now, couldn't figure why.
hello zorin, can you detailed the connection using the ac transformer to the board to avoid blowing up the 3 ic's, planning to follow these project of yours. thanks a lot.. a follow up video or explanation is so much appreciated. more power to your channel. :)
Love the video😊I have the same power supply. It arived from china with dead amplifiers, and after few day transistor and big rezistor died😅I replaced them by original ST tranzistor and royal ohm rezistor and it works without problem😊
Yes! A lot of people don't seem to get that. If you short the output, and a good bench supply should be able to handle that, the transistors will dissipate power equal to the 5 ampere current limit times the *unregulated* voltage, so something greater than the full rated output power of the supply. If the output can deliver 30 V and 5 A, the transistors would dissipate probably something in the range of 160 to180 watts.
@@d614gakadoug9 This is the reason why I was asking. Besides, an even better power supply would have a transformer with multitap secondary and an automatic relay logic to select the input voltage to never have a voltage drop on the output transistors greater than a certain maximum, to limit the power dissipated by them.
This guy is adorable! I like watching his videos, but this one is hilarious too. Kind of ElectroBoom. Depending on what you need the PSU for, I would consider buying 60$ labor PSU for repair and diagnostics.
Yes, usually is more comfortable to work with a 60$ PSU, but for some applications like developing an audio device with minimum requirements of noise linear PSU are the way to go.
29:00 You are wrong. Here the variable resistor has to deal with 100W, the transistors not. If you configure a low output voltage at max current, then the transistors has to deal with 100W. I guess they will desolder from heatsink and blow up. Lets try. 😂
@@electronicsrepairschool No. The transistors are passing 5 amperes, that's true. But they will not dissipate 100 watts before they at the same time also have 20 Volta across collector/emitter. If you crank up the voltage to maximum it only be the Vce (of a bipolar transistor) times the current that is dissipated in the transistor. But if you set the output voltage to 1 volt and the transistors is fed 21 volts, then they have to "remove" / burn up the voltage difference which would be 20 volts. And at 5 amperes that would equal 100w of heat there.
@@electronicsrepairschool No, because if you have 24 V input, 20V output and 5A current, over the transistors you will have 4V drop. That means 20W of power disipation. If you have 24V input, 4V output and 5A, then you have 20V over the transistors and they have to tranfsform 100W electrical power into heat. That would be a real test. 🙂
I understand your point, actually is very easy to calculate, but, when you design/test a power supply, you take in consideration the worst case, in this case hare are not relays to switch the transformer output for low vce
@@electronicsrepairschool So why you didn't make the test with 1V output voltage and 5A output to show how hot the transistors can be ? With 20V output voltage is nothing to them.
If you slow down the video, it literally looks like some voltage flies from the right corner of the screen and trashes your 5v out. I'm not sure what happened there, but it looked like something zapped it's tiny ceramic capacitor from several inches away on your work bench.
Nice video.keep going sorin,may i ask what model is the camera you record with the one you use to record from top,i checked you tools link but you haven't included
What I think happened is the bottom of the small DC-DC converter touched the copper heat pipe which is soldered to the collector of the big transistor, so.........you can figure out the rest :))
@@repairtech9320 The odd thing is the spark appears to originate from the transistor soldered to the heatsink, rather than the dc-dc converter. After the spark the capacitor on the dc-dc board glows red before it burns up, Not watched any further yet, so will see what else happens...
On mine the output to the display is up to 33v. Connected as you do. The display is rated 4.5 to 30v. I touched its components and the transistor gets very hot. So a step down regulator is needed?
Hi, Ive been looking for one of these that works correctly.. I have seen another channel that can only get 23V from the board. @8.35 you get 23V with a 24v AC transformer. 24v AC rectified to DC gives 33.9V DC, with a little loss here and there in the circuit the output max should be 30V DC. Have you managed to find the fault and fix this?
If I insert a 24volt Zener diode in the regulator ground lead this will in effect increase the max output to 48 volts which is what I need , however can the rest of the components take the increase in voltage?
I bought the same kit but from a chinese site. The parts came mixed together in a bag, for most parts is not a problem but I got 6 tiny glass diodes, identical looking, 4 of them are supposed to be 4048 diodes and 2 of them are supposed to be 5.1V zenner diodes. How can you identify which one is which ? You can build a circuit with a resistor, a diode connected in reverse, a variable power supply and increase the voltage gradually, if it starts conducting above 5.1V is the Zenner, but is kind of complicate if you do not have yet a variable power supply. Suggestions ?
@@urnoob5528 There is nothing written on the glass except the black ring marking the cathode. The diodes are half the size of a grain of rice, even if it was anything written it would have been impossible to read with a naked eye.
@@klaasspoelstra7439 Nope, they are identical, both the zenners and the regular diodes use DO-35 packaging (1.5mm diameter, 3.4mm long). I had to use use a resistor in series with the diodes and zenners and see which ones connected in reverse started conducting above 5.1V. After this I also noticed on the multimeter the forward voltage drop was different, I think the zenners had a 0.55V forward voltage drop while the 1N4148 had 0.7V forward voltage drop. On another channel I saw someone assembling this kit and in his case the zenners were delivered still embedded in the paper strip roll.
OK George, measuring them is the best solution. When you finish the kit you can use the cc method to identify zeners. I use by the way a magnifying glass and then is the 5v1 or 4148 imprint more or less visible. I already finished the kit and it works fine. I used IC-sockets, changed the op-amps for 741 (higher voltage tolerance) and attached a big cooling plate and no fan.@@georgedone7997
how much would a transformer like that cost? OR...for hobbyist applications, what power should the transformer have or does this thing even matter and just the output voltage which has to be 24AC?
The little dcdc regulators need good output caps (x5r or x7r) and Chinese wants more profit so they put junk caps. Simply check ripple with dmm set to ac mode.
Hello, interesting video. Can you share the parts to understand how it works (Transistors, chips...) Thanks. BTW, can we replace those transistors by N Channel mosfets ? (more available and can take more current)
Great switching mosfets are not necessarily great in a linear supply. I would guess that the transistor package and heat sink (and the voltage difference/power dissipated) determine how much current it can take.
Hi sorin great video again I would love to see how you would build or modify a ebike motor controller I want to make one that can maybe run with 1 36v battery and be able to adjust or just boost the power to the motor for short periods or to run it at 72v I think it would be a good video especially using your special calibrated wires 😂 ect. Thanks for all the really helpful stuff you have taught me, hope you are well.
Hello guys! I'have built this kit with the recommended modifications what Sorin mentioned here. I used a 30V/6A transformer.After some research I replaced the opamps with TLE2141 chips, used 10A rectifier diodes, and higher wattage resistors. Replaced the main cap with 4700uf 50V. Connected the transistors in parallel using resistors on the emitters. Everything seems to be the right way around, but when i power it up (without load), my LED is always on and i can adjust the voltage only up to 8V, and I noticed that one of the opamps (near the trimpot) is getting very hot, so I wasnt keeping it plugged for a long time. Ive read on some forums that the trimpot should adjust the value of the resistor next to it (270k). On mine it doesnt seem to work. Now im stuck with this problem, Does anybody has an idea what should i check? I have a very basic electronic knowledge so far. Thank you guys
The very first thing to check is the supply voltages for the op amps. Unless the transformer you have is *very* conservatively designed it very likely has the turns ratio adjusted to give the nominal output voltage at or near the full rated current. If that is the case the voltage with no load will be greater than 30 V. The peak voltage even with just 30 V will be 42 volts. It wouldn't surprise me if the peak voltage with no load was very close to 50 volts. The filter capacitor will charge to that voltage when there is no load. As I understand it, some or all of the op amps on the board use the unregulated DC voltage for their positive rail and some small negative voltage (-5 V ??) for their negative rail. If that is the case the total voltage between the positive and negative supply rails will exceed the absolute maximum allowable for the TLE2141 (44 volts). EDIT: I found photos of what I believe to be the same board and confirmed that the op amp positive supply pins are all connected to the unregulated DC at the main filter capacitor. I couldn't see enough detail to really confirm the -5V supply, but that's what it looks like. If the voltage is too high there is no easy solution. There are very few op amps that will run at greater than 44 volts. They do exist, but there isn't a lot of choice. If an amp is being used to drive an emitter follower power stage, which is quite likely, the maximum output voltage you'll get from the supply would be a few volts less than the positive supply voltage for the amp, so regulating the amp's power supply will also limit the output voltage you can get. If your transformer has a centre-tapped secondary, I would suggest trying to get the regulator board working using just half of the winding (i.e. centre tap to one end; leave the other end open). This will limit the voltage you'll be able to get but get the unregulated voltage down to where everything should be safe from overvoltage damage. Again, measure the power supply voltages for the op amps. If they are more than 22 volts between the [+] and [-] rails when using half the transformer voltage, you simply can't use the full winding without modifications to the board. Those mods are probably beyond what you can figure out how to do if you only have basic knowledge.
Thank you for the explanation! Yes it seems this 30V transformer was a bit of an overkill for this design. Sadly it doesnt have a center tap. I will try to source another transformer with lower voltage and continue testing .
@@d614gakadoug9 Here in UK we have 240v mains supply, my supply is usually around 245volts, so if using Chinese transformers designed for 220volts output voltage off-load will be much higher than nominal voltage. I used two 18-volt transformers as I didn't have centre-tapped one. Output voltage was OK up to 25-volts, but current limiting didn't work as supply to op-amps was too low. Shunting series resistor in supply to op-amps restored op-amp voltage to near normal. Tried reverse engineering circuit, but was not easy, but found a circuit on Mile Kokatov, Z33T, webpage together with excellent article with suggested mods. For low currents you can use one non-center-tapped transformer with two diodes connected as in voltage-doubler circuit, fed to the 3-terminal AC-input. Positive end of one diode to one side of 24v input and negative of other to other side of 24v input. The remaining connection of the transformer goes to the center-tap of the input.
Hello. The problem was the short that was mistakenly made when regulator board touch the heatsink pipe, which is from copper. One must be more cautious.
Buna dimineata! Can you tell me more about the transformer? How many Watts or Amps does it have? I like this project, but I am afraid If I put it in a case, the transformer will be the first to burn. That and adding a breaker on the output so it clicks instead of blowing a laptop up LOL. Mulțumesc!
Sorin be careful, warming up a heatpipe that much can very easily make it explode. And if it doesnt explode, it loses some of the ability to move heat to the heatsink
This smoll green 5v-12v bastards used a lot in fpv drones, for various purposes, powering a gimbals, eleron/rudder servo machines, ets. And them diying a lot for millions reasons, me and friend crash a lot rc planes before start using good quality dc-dc converters :) But at least we have a lessons :)
12:39 minutes I think you didn't know the maximum voltage input of your mini step down dc to dc converter, which is connected to your cooling fan , i saw that smd filter capacitor burn out, as I've zoom in the video, 😅 you mishandled it don't you, better luck nxt must check your module's capacity input before connecting into the input supply 😢
Hello, Question, I didn't fully understand your toroidal transformer. You mentioned that it's small one. And it was still capable of outputting 5.3A? What is the rating of your toroidal transformer? Was it rated to output 5.3A? I ask this because I am interested in the transformer's point of view. If the transformer is rated for max "lets assume" 3A secondary max current. And you squize out 5.3A that means it was overheating and it could be destroyed if you would run it a bit longer? And on other hand... if toroidal transformer would be rated for max secondary current output of "lets assume" 8A. Also the Linear Adjustable Power Supply could see the 8A instead of 5.3A right? Or am I wrong? Very interesting and good video. In this video Best regards, P.S.: I don't quite have this part of electricity figured out at the moment. But I would like to clear it up a little. Because I want to make a simple audio amplifier (with TDA7294V) in the future and i don't know which toroidal transformer to buy regarding the needed output currents... not destroy the transformer if amplifier would need alot of current...
If your transformer can't handle the current drawn, the voltage will drop severely and its core will overheat , which can sometimes lead to melting( in severe cases). If your transformer can handle more than the current which the supply can draw, you will have a more stable voltage output but you will not get more amps on the supply output. As for the TDA7294 amplifier, If you make it stereo, you will need a transformer with a voltage of 2X25VAC and about 350VA.(You will have 2x35,25VDC after rectifying and filtering) You must use only 8 ohm speakers when you use a +/- 35V supply!
Determining the current rating for a transformer can be quite complex. Usually transformers are rated for RMS current. When you rectify and capacitively filter the output of a transformer, the RMS current from the transformer will be greater than the average current you draw on the DC side. The higher the capacitance you use, the higher the ratio of RMS current to average current. (What happens is that current only flows if the instantaneous voltage of the transformer secondary is greater than the voltage on the capacitor. That means that the current typically only flows for a small fraction of each half cycle, but the amount of current is much larger than the average DC. The RMS value of those current pulses can be very high.) Audio makes things more complicated because you very rarely continuously draw full power from the power supply. Usually with audio you can get away with using a transformer with lower current rating than you might for a bench supply that would continuously deliver. It is perfectly OK to draw more than rated current from a transformer as long as the long-term current is within the rating and the over current isn't drawn for very long. What you're really trying to do is keep the peak temperature of the copper windings within allowable limits. Remember that power dissipation in a resistor is proportional to the square of the current though it. The windings have resistance. If you draw 150% of rated current the resistive losses in the windings will be 1.5² or 2.25 times what they would be at 100% of rated current. If you draw 70% of rated current the resistive losses in the winding would be 0.7² or about half of what they'd be at 100%. Some manufacturers of transformers publish applications information to help you determine what you should use.
@@Atelierul29 Thank you very much for your reply and help (I replied to your comment I think the second day after posting but I don't know why it doesn't show it. I'll reply again). As you guessed I want to make a stereo TDA7294 audio amplifier. You mentioned that for the TDA7294 I would need 2x25V AC which would eventually come out to 2x35,25V. You mentioned that you recommend 350VA. I looked at what options I have to choose from regarding transformers and I found. Option 1: MULTICOMP PRO VTX-146-300-125 which can deliver max 6A current (Not as expencive as 500VA) I looked at the datasheet of the TDA7294 Audio Amplifier and I see that it has a output Peak-current of 10A. So would I need a more powerful transformer? let's say Option 2: MULTICOMP PRO VTX-146-500-125 (To me little too expensive) which can deliver 10A of current. And since I need 2x IC TDA7294 to make a stereo then I would probably need a 500VA transformer? Yes, it's true. On very, very rare occasions I will have the volume up to max. And it is probably very difficult to get to a peak-current of 10A and maybe from that we can conclude that a 500VA(max.10A) or even a 300VA(max. 6A) transformer would be sufficient? Also, may I ask why I should only use 8ohm speakers? I currently have 6ohm speakers at home which I would like to continue using (this would save a little on cost of this wanting DIY project). I know that if I have 6ohm speakers they will require more current from the amplifier which probably the 300VA transformer would not handle. But how much current change are we talking about? I have no idea. realy rough assumption - would 8ohm speakers need 6A and 6ohm speaker 8A?
@@d614gakadoug9 Thank you very much also for your reply and clarification. It was very helpful. And I understand what you wanted to say. However, it is still interesting to me that such a small toroidal transformer in the video can deliver 5.3A without the transformer heating up. For example, I am now looking at (from a previous reply) a MULTICOMP PRO VTX-146-300-125 transformer which weighs 3kg and has the capability of delivering 6A current. Interesting, I have no concept yet why such a small transformer could deliver such a current without troubles.
I believe that regulator output has touched the heat sink which is directly connected to the collector of the big transistor which caused that Cap to blow
Yep.
yes - i think thats what happened too
if it was 230V regulator he would notice it 😂
@@nicmate2543
absolutely 😄
I'm surprised Sorin missed that. I see that a plastic insulator magically appeared under the replacement. I was waiting for the increasingly hot rheostat to be dropped onto the power supply.
I built that kit in 2019 - building it into a housing and added 10 turn pots and a Volt/amp meter. And it works great !! Best thing ...... unlike many of the constant current power modules you can buy - this one actually does a great job with current limiting !! It actually limits current down to 2.5 mA. Great for power injection and testing diodes !!
Same. I killed the first opamp from the output side with arking a street light ballast inductor. Perfect supply for the price. The input AC voltage is critical: the opamps use the full voltage rail with the -5V.
12:40 if you go frame by frame first you see big spark that looks like it comes from transistor and then smoke + red glow from the capacitor on voltage regulator for the fan. I think that regulator touched fan pipe and capacitor on fan regulator shorted over the transistor 😎.
FYI when you pause the video you can move forward and backwards frame by frame by comma and dot keys on the keyboard 🙂.
Great tip on using the comma & period for frame by frame. Thanks!
Gotta love the fact that your videos are so "organic". You also include fails along so we can learn from that, coming to a conclusion in the end and learning a new fix or a new way to blow up electronics, haha. Keep it up, Sorin! Looking forward to the next upload. Have a nice evening
The best way to learn electronics is this building something from zero. Nice one
beware!!! :D
that kit is wellknown, and have some flawless, too.
the most easier flaw to fix is using for AO's a local power supply, like a Zenner and a resistor, calculated for no more than 30V over AO's, negative power included!
it's a -5V on negative, so, 30-5=25, but there are no 25 V Zenners, not 3 terminal stabs, so, 24 volts.
most easier is to use the already present 24V, for cooler.
some small adjustment for resistors, and is perfect.
of course, you need a nicely strong mains trafo, 24V or a bit more. or a bit less, if you accept a bit smaller voltage on full load... :)
(written immediately after i seen the kit... is a wellknown for me! :D now, play to the finish... i'm really curious what you will find about... as a side note, is a really antique schematic, older than 60 years, in some variants. one of them use 3/4 AO's in a 324, and the last one is used as overload indicator, doubled as relay activator... :P )
later: min 13: to much current on a diode in the bridge! it's what happens most of time, without dealing with small smps's :D
also, looks like you don't set the 0 volts, that blue multiturn is used to set the 0 volts, because this is a "virtual ground" power supply. for same reason you fried it first time with a 19 v laptop brick! :)
lemme see... you just repeated the very same mistakes me and a lot of people does for the first time they meet this schematic, and, later, this kit... chinese started to manufacture and sell those kits some 15-18 years ago! :)
i patiently seen the video to the final... Sorin, that blue led is NOT "power on" led, but "overload led", it need to be on only when you load the PS with more than your current limit! :)
why is all the time on? some of these kits are correct, some not... some have a slight different schematic than the original in that part, and led is on the opposite directions, and is on all the time. other kits have wrong orientation printed on pcb.
looks like electronics-diy point com shunned out that power supply, even this was their top-grade reason to check their website, a lot of years...
you can find a lot with a google search, but i have trust in "radioscamateurs" sites, so... check the link down. i have not patience to search exactly about setting-up procedure, i had done it for some kits, and leaved it alone...
also, with a bit of more searching, you can find a giga-talk about that schematic on a romanian forum, in power supplies section. a forum i leaved it for some years, even if i was one of the only posters there, for a lot of years, too... :)
să fii iubit. :)
www.qsl.net/z33t/dc_0-30v_0-3A_eng.html
Do you think is possible to kill this kit by connecting a cara battery to It with out the Power supply be set to a voltage above the battery voltage?
12:39 You shorted the little switching power supply with (heatpipe cooler) the collector of the transistor
As built the transistors are passing 5+ Amps (100+ Watts), but they are not dissipating anything near to that, which is why the fan/heatsink are coping and the transistors remain fairly cool. If you hooked up a 35V transformer as you suggested, then particularly when used at lower voltages the transistors will be dissipating much more power and thus get hotter, to the extent that you'll probably need a bigger fan/heatsink combination. Which is why many power supplies switch transformer windings in and out dependant on the voltage required at the output.
Learning by doing is the best way to lean and to achieve experience and not be afraid of the unknown or new. Smoke is good, smoking lessons from Sorin are funny, familiar friendly and very infesting always. All the best “moșu!”. Big hug!Cosmin from Switzerland 🇨🇭!
I noticed that your current limit led is constantly on, it should only come on when the current limiting kicks in. On my board the silkscreen had a error and the transistor that controls the led needs to be rotated 180 degrees that will make the led work correctly.
I originally posted something like this in response to someone's question, but it seems a lot of people miss the issue, so I'm posting again with some elaboration.
This is intended for use as a bench power supply. With a bench supply you really need to be able to deliver full rated current into a short circuit or close to a short. You may not need to do this often, but the need does arise.
Your power supply needs to be able to survive it.
When the output current is set to maximum and the output is shorted, the power dissipation in the transistors will actually be more than 100% of the full rated output power of the supply. If the supply is rated for 5 A and 30 V, that means the transistors would dissipate 150 watts, *minimum.* If fact the dissipation will be even greater because the voltage across the transistors will be equal to the full unregulated voltage from the bridge rectifier and filter capacitor. For the 30 volt supply that might be 35 volts (or more). At 35 volts the transistors would dissipate 175 watts at 5 A. That is a lot of heat to get rid of!
If you use the regulator for some specific application where the output voltage is not very low, the situation is different.
With high powers it is important to be careful that the transistors used have adequate safe operating area. "Second breakdown" can limit the allowable steady-state power dissipation to something well below the nominal rating of the device. With low voltage this often isn't a problem, but it very definitely becomes a problem when you get up into tens of volts.
The little buck converter board was sitting right on top of the copper heat sink. Wild!
It's funny... you went from "Electronics Repair School" into "ElectroBoom" in this video... loved it Sorin... :)
i built two of the power supplies powered up and op amps burned up so i change op-amp to lm741 because higher voltage rail and use dip sockets. i also also use 2n3055 as output transistor. used if for five years now
Nice! I build several working great though...but take care and replace IC with good ones, I'm using TL701 instead ''originals'', also I replaced R7 with 3x1ohm/5W in parallel , gives like 0.33 and let more current flow too.
did it ever work with the original op amps at all? Mine never worked with the originals, nor with the replacements I used (not a FET op amp, but no difference in behaviour)
now I finally know for what I order bunch TL701 three years ago :D
@@AnnaVannieuwenhuyse my worked fine with originals but I somewhere read that they're very sensitive to overvoltage so I probly order replacement at same time. But PSU end up lost in mail for half a year so I in the end never really used it, just assembled and tested.
do u know where i can buy transformer? 20v 5A
@@VanDuc1126 I built mine ruclips.net/video/yxEW2CWy4ew/видео.html
Fantastic, Sorin. My linear power supply i made with atx desktop power supply, using - cable blue -12v and yellow cable + 12v with aliexpress regulator 2956. -12v with +12v i have + 24v alright? Also, have a generic aliexpress meter voltage/current (als288 maybe) conected in serial mode with out - and out + . I am using 1 year no problem, but, i recomend using diodo retificator 4amp in +12 (its possible calibrate diference 0.7 volts on meter adjust) Its my homenade power supply setup; DIY Ever!
It's not only you, when I try to build something to show someone, sometimes I have such "luck" as well.
13:35 - Strange thing you didnt stop video recording and check what sparked. Its power supply for fan, little capacitor. 12:39 spark.
I believe that green pcb touched heatsink, and heatsink is soldered to the back of that big transistor. 18:29 you placed isolation tape on back :D
Definitely enjoyed this one, Sorin. One of your best. Please do more like this. It was funny with the flashback to the original barbecue video/livestream, too!
I went thru this adventure a couple of years ago and I was unlucky at first. Transistor blew up almost instantly at 2 amps. Later I got scammed with fake Toshiba transistors on amazon. Ended up using a 13007 extracted from an old ATX psu and problem was solved. If you have a proper power transistor with proper heatsinking, the thing does it's job. Have in mind that with this circuit, if it overheats and shorts, it will send the full unregulated power to whatever you have connected at the output.
is there a mod to avoid this? have a similar experience. thanks for the 13007 tip.
@@spimfurt I don't know of any specific mod for that right now, I haven't done my research online. But it is actually a project I have been really wanting to make. I think by using a comparator IC we could make some kind of overvoltage protection that triggers a relay if it goes much higher than the voltage set.
The voltage on the output rectifier and capacitor filter is 24*sqrt(2) = above max rating of 7812
And seems small switching regulator short to the heatsink
Maximum voltage for regulators between 5...18V is 35V, so 33,84V is under the maximum limit. Any datasheet will confirm that!
Nice video! Just one comment, you said the heatsink/transistors need to dissipate 100watts. But I guess most of the 100 watts gets lost as heat in your resistive load. You could measure it.
Why measure anything when he had all numbers in from of him on that little screen? Almost 20Vx5A=100W. But yes, in a resistor, transistors only dissipate difference between input and output voltage (xA of course) so around 25W with that transformer
Correct . A piece of copper wire carrying 5amps at 20volts does not dissipate 100watts!..it’s 5amps x the voltage drop of the wire !
With this sort of supply you need transistors and heatsinking adequate to handle the full rated output current with the output short circuited, or nearly shorted. That means that probably something in the range 120 to 150% of the rated normal maximum output power is dissipated in the transistors (the dissipation is the product of the output current and the *unregulated* voltage ahead of the transistors - i.e. on the main filter capacitor).
How can we add the relay for clicking effect of short circuit?
Good question!
on hight currents and low voltages, the powersupply is capable of one, but loud, click. but for real, that blue led goes off, when the short is present.
Thank you, your videos make electronics fun again.
so satisfying to watch the soldering process
Hi Sorin, is current limiting functional? That diode on the pcb should light up only when overloaded. I have made a double stabilized source from these modules. And I had to replace all the ICs on both. And many other changes besides. Try to short-circuit the source, with a set current of 3A, and then you will see what the temperature will be on the transistors. :)
You have right, only if in short that led will be light
That regulator for the fan made contact with the copper from the cooler and got shorted because you didn't isolated the board under! 🤣🤣🤣
Would love to see an updated version video with all the mods you suggested a case and some testing done to it using your oscilloscope on the output for example. Plus if any more mods you can think of... Thanks for sharing though!!
i bought this a year ago. the achiles heel here is the low voltage and high current. a 3V motor powered by 1.4V and 0.8 - 1.5A for an hour caused the failure of the big transistor. the loud one. sorin, i will appreciate if you can find a way to make this power source to sustain 0.8V and 3A forewer. typicaly for ram/cpu power testing. for cooling i used the 775 heatsink from intel quad core cpu. no fan. transformers are available in some cheap speakers with amplifier. usually 2.5A, -11 and +11V = 22V. or this expensive sorins fancy toroid.
Quite hard but not impossible. In the situation you mention It Will dissipate more than 60w in heat. You Just use a bigger transistor and Active cooling
really the case for any linear supply
As always Brilliant Just wished you pointed out how important the input toroid/transformer is.
Salut Sorin. eu am facut aceasta sursa de alimentare si tot mi se ardea OP-ampurile si nu stiam de ce. eu am cumparat un traf toroidal de 24v AC dar in gol scotea 27V. traful trebuie sa scoata fix 24 V in gol ca sa nu arda integratele. 24V AC inmultit cu constanta capacitiva de 1.4 dupa redresare si filtrare o sa ai in jur de 33.6V maxim. cu 27V in gol inmultit cu 1.4 ne da 37.8V care ard integratele pentru ca nu sunt proiectate pentru o astfel de tensiune. tensiunea maxima admisa pentru TL081 este de 30V DC. ce este peste le arde si nu stiti de ce sursele nu functioneaza. pentru integrate folositi un soclu si a-ti scapat de problema cand ele se ard. frumoase videoclipuri Sorine. Ma bucur ca avem asa romani priceputi si peste hotare. o zi faina!
how about a hybrid powersupply? there the final regulation is done by a transistor operating in its linear region - but a switching mosfet pre regulator - that tracks the voltage to say - 3volts higher than the transistor to make the power that the transistor has to turn into heat that much less?
Or multi step transformer, like 0-5-10-15-20-25-30V.
That can work quite well though dynamic performance may not be as good as with an all-linear design.
You still need pass transistors rated for the maximum input voltage so that if the load is abruptly removed after running at full voltage (meaning the switcher is putting out its max voltage) the transient input-output differential across the pass device won't kill it.
If the load is very abruptly increased it may take the switcher a bit of time to "catch up." With modern designs running at quite high frequency and carefully done for good dynamic performance this may not be an issue.
I have watched quite a few videos of amateurs making power supplies. So far not a single one has done anything at all to test dynamic performance. Poor dynamics can lead to voltage drops which can cause circuit misoperation but usually aren't disastrous, or overshoots that can destroy circuitry being powered. Everybody just connects a meter and calls everthing good if the meter looks stable. Well, the typical DVM will show you 25 volts for a 5 kHz 100 V rectangular waveform with 25% duty cycle, so ...
Great tutorial! Nice music at 23:55 😉
there is that properly calibrated wire love it man thanks for video been trying to find parts for making one from junk tvs
I built one of these kits, but haven't had a chance to even check if it works, as I don't have a suitable transformer. it was an entertaining enough project, and maybe I'll find a decent 24v transformer in something at some point in the future to test it out.
Old 24V UPS is a great source.
Well, you can power it with DC without any modifications.
@@ivankirola2707 You can't, it won't be able to generate the negative rail it needs.
I still have this kit somewhere assembled, ending up never using it but is there as backup, just in case. I got it for free because it was lost in mail somewhere so aliexpress give me refund, package arrive 6 months after that.
btw fan will have much more problem with lower voltage, with 19V transistors don't need to drop too much but if you lower your voltage to lets say 1V and try to push 5A for long time that little heatsink would have hard time :)
Mulțumesc, Sorin. I wasn't sure how I was supposed to connect the Ammeter to the supply. My attempt resulted in the D882 transistor shorting out because I tried powering the meters from the fan output. Tried your method and it works flawlessly!
hi Sorin, I'm using this circuit since 6 yrs. lately D882 get burnt, I replace it but agian burnt, I found the cap 0.22u next to D882 damaged I replaced with used one works for a while but again D882 get burn i remove the cap and it worked fine till now, couldn't figure why.
hello zorin, can you detailed the connection using the ac transformer to the board to avoid blowing up the 3 ic's, planning to follow these project of yours. thanks a lot.. a follow up video or explanation is so much appreciated. more power to your channel. :)
I bought few years ago one of the RD tech power supplies from aliexpress, I have a 32V 5A and it's been very good.
but it is not linear . it is switching and you have ripple
Love the video😊I have the same power supply. It arived from china with dead amplifiers, and after few day transistor and big rezistor died😅I replaced them by original ST tranzistor and royal ohm rezistor and it works without problem😊
23:01 Do the transistors bear 5A on a short circuit, when they have to dissipate all the power?
Yes!
A lot of people don't seem to get that. If you short the output, and a good bench supply should be able to handle that, the transistors will dissipate power equal to the 5 ampere current limit times the *unregulated* voltage, so something greater than the full rated output power of the supply. If the output can deliver 30 V and 5 A, the transistors would dissipate probably something in the range of 160 to180 watts.
@@d614gakadoug9 This is the reason why I was asking. Besides, an even better power supply would have a transformer with multitap secondary and an automatic relay logic to select the input voltage to never have a voltage drop on the output transistors greater than a certain maximum, to limit the power dissipated by them.
@@you2ber252
Switiching taps can result in poor dynamic performance. It is much more common in cheap supplies than high-end bench supplies.
@@d614gakadoug9 We're talking of hobbyist gear here
Use your new oscilloscope on the outputs to see how noisy it is
It's a linear, regulated power supply. The noise will be very, very little, almost nonexistent.
@@Atelierul29 ruclips.net/user/shortszF4elc9cnzM
When you put the variable resistor on the bench next to the toroid you got an induced current which was too much for the capacitor.
You are going too far away! He shorted it to the heatsink.
you need to fetch 2A output @2V to feel the hotness at the transistors.
This guy is adorable! I like watching his videos, but this one is hilarious too. Kind of ElectroBoom.
Depending on what you need the PSU for, I would consider buying 60$ labor PSU for repair and diagnostics.
Yes, usually is more comfortable to work with a 60$ PSU, but for some applications like developing an audio device with minimum requirements of noise linear PSU are the way to go.
29:00 You are wrong. Here the variable resistor has to deal with 100W, the transistors not. If you configure a low output voltage at max current, then the transistors has to deal with 100W. I guess they will desolder from heatsink and blow up. Lets try. 😂
Who is delivering the 100W to the resistor? :D Actually based on the transistors efficiency, for 100W output, the transistors has to deal around 130w
@@electronicsrepairschool No. The transistors are passing 5 amperes, that's true. But they will not dissipate 100 watts before they at the same time also have 20 Volta across collector/emitter.
If you crank up the voltage to maximum it only be the Vce (of a bipolar transistor) times the current that is dissipated in the transistor. But if you set the output voltage to 1 volt and the transistors is fed 21 volts, then they have to "remove" / burn up the voltage difference which would be 20 volts. And at 5 amperes that would equal 100w of heat there.
@@electronicsrepairschool No, because if you have 24 V input, 20V output and 5A current, over the transistors you will have 4V drop. That means 20W of power disipation.
If you have 24V input, 4V output and 5A, then you have 20V over the transistors and they have to tranfsform 100W electrical power into heat. That would be a real test. 🙂
I understand your point, actually is very easy to calculate, but, when you design/test a power supply, you take in consideration the worst case, in this case hare are not relays to switch the transformer output for low vce
@@electronicsrepairschool So why you didn't make the test with 1V output voltage and 5A output to show how hot the transistors can be ? With 20V output voltage is nothing to them.
If you slow down the video, it literally looks like some voltage flies from the right corner of the screen and trashes your 5v out. I'm not sure what happened there, but it looked like something zapped it's tiny ceramic capacitor from several inches away on your work bench.
12:38 Sorin, the power supply specialist! 🙂
Regulators dont need to dissipate the full power to the load i.e. 100W but a fraction of that, that's why your fan made it.
Nice video.keep going sorin,may i ask what model is the camera you record with the one you use to record from top,i checked you tools link but you haven't included
What I think happened is the bottom of the small DC-DC converter touched the copper heat pipe which is soldered to the collector of the big transistor, so.........you can figure out the rest :))
in slow motion you can see the spark coming out from under the 5V PS shorting on the heat pipe
@@repairtech9320 The odd thing is the spark appears to originate from the transistor soldered to the heatsink, rather than the dc-dc converter. After the spark the capacitor on the dc-dc board glows red before it burns up, Not watched any further yet, so will see what else happens...
@@will_doherty true
On mine the output to the display is up to 33v. Connected as you do. The display is rated 4.5 to 30v. I touched its components and the transistor gets very hot. So a step down regulator is needed?
Hi, Ive been looking for one of these that works correctly.. I have seen another channel that can only get 23V from the board. @8.35 you get 23V with a 24v AC transformer. 24v AC rectified to DC gives 33.9V DC, with a little loss here and there in the circuit the output max should be 30V DC.
Have you managed to find the fault and fix this?
but Sorin. The transistiors are not actually consuming 100W, so cooling should be fine. most of the power is taken by the resistor/load
If I insert a 24volt Zener diode in the regulator ground lead this will in effect increase the max output to 48 volts which is what I need , however can the rest of the components take the increase in voltage?
Sir, please can you tell me that, can i use ATX computer power supply for this linear regulator input. If not why?
Can you please show the quality of its signal on the new oscilloscope you bought?
I bought the same kit but from a chinese site. The parts came mixed together in a bag, for most parts is not a problem but I got 6 tiny glass diodes, identical looking, 4 of them are supposed to be 4048 diodes and 2 of them are supposed to be 5.1V zenner diodes. How can you identify which one is which ? You can build a circuit with a resistor, a diode connected in reverse, a variable power supply and increase the voltage gradually, if it starts conducting above 5.1V is the Zenner, but is kind of complicate if you do not have yet a variable power supply. Suggestions ?
read the damn words on the glass
@@urnoob5528 There is nothing written on the glass except the black ring marking the cathode. The diodes are half the size of a grain of rice, even if it was anything written it would have been impossible to read with a naked eye.
13:17 the zener diodes are the bigger ones
@@klaasspoelstra7439 Nope, they are identical, both the zenners and the regular diodes use DO-35 packaging (1.5mm diameter, 3.4mm long). I had to use use a resistor in series with the diodes and zenners and see which ones connected in reverse started conducting above 5.1V. After this I also noticed on the multimeter the forward voltage drop was different, I think the zenners had a 0.55V forward voltage drop while the 1N4148 had 0.7V forward voltage drop. On another channel I saw someone assembling this kit and in his case the zenners were delivered still embedded in the paper strip roll.
OK George, measuring them is the best solution. When you finish the kit you can use the cc method to identify zeners. I use by the way a magnifying glass and then is the 5v1 or 4148 imprint more or less visible. I already finished the kit and it works fine. I used IC-sockets, changed the op-amps for 741 (higher voltage tolerance) and attached a big cooling plate and no fan.@@georgedone7997
Hello Sorin. Will you be installing small value resistors in the emitters of the those 2 transistors?
I feel really good about my soldering skills after seeing this 😂 but seriously thank you for showing me this kit
Is it possible to use laptop mosfets to build a power supply. They have 30am ratings . Maybe some way to re use from old motherboards?.
how much would a transformer like that cost? OR...for hobbyist applications, what power should the transformer have or does this thing even matter and just the output voltage which has to be 24AC?
The little dcdc regulators need good output caps (x5r or x7r) and Chinese wants more profit so they put junk caps. Simply check ripple with dmm set to ac mode.
Whats the negative voltage doing in the curquit????
I have lot of d288 mosfet , i am searching project power supply for using this mosfets
Please, do you have a solutuon with what We can change the transformer ?
thanks Sorin,
I bought the same kit, what kind/rating Transformer should i get for this kit to be able to get 30v 3A out of it?
I have a switchmode power supply (50v 10amps) and i want to regulate the current to constant current 6amps
How can i go about it
Ive been expecting this so long thanks Sorin
Hello, interesting video. Can you share the parts to understand how it works (Transistors, chips...) Thanks.
BTW, can we replace those transistors by N Channel mosfets ? (more available and can take more current)
Great switching mosfets are not necessarily great in a linear supply. I would guess that the transistor package and heat sink (and the voltage difference/power dissipated) determine how much current it can take.
When I test it for current calibration using 10 ohm resistance 33 ohm resistance gets smokes why
Hi sorin great video again I would love to see how you would build or modify a ebike motor controller I want to make one that can maybe run with 1 36v battery and be able to adjust or just boost the power to the motor for short periods or to run it at 72v I think it would be a good video especially using your special calibrated wires 😂 ect. Thanks for all the really helpful stuff you have taught me, hope you are well.
Sorin, I keep trying to figure out what soldering iron you have, can you please let me know. Thank you
Hello guys! I'have built this kit with the recommended modifications what Sorin mentioned here. I used a 30V/6A transformer.After some research I replaced the opamps with TLE2141 chips, used 10A rectifier diodes, and higher wattage resistors. Replaced the main cap with 4700uf 50V. Connected the transistors in parallel using resistors on the emitters. Everything seems to be the right way around, but when i power it up (without load), my LED is always on and i can adjust the voltage only up to 8V, and I noticed that one of the opamps (near the trimpot) is getting very hot, so I wasnt keeping it plugged for a long time. Ive read on some forums that the trimpot should adjust the value of the resistor next to it (270k). On mine it doesnt seem to work. Now im stuck with this problem, Does anybody has an idea what should i check? I have a very basic electronic knowledge so far. Thank you guys
The very first thing to check is the supply voltages for the op amps.
Unless the transformer you have is *very* conservatively designed it very likely has the turns ratio adjusted to give the nominal output voltage at or near the full rated current. If that is the case the voltage with no load will be greater than 30 V. The peak voltage even with just 30 V will be 42 volts. It wouldn't surprise me if the peak voltage with no load was very close to 50 volts. The filter capacitor will charge to that voltage when there is no load.
As I understand it, some or all of the op amps on the board use the unregulated DC voltage for their positive rail and some small negative voltage (-5 V ??) for their negative rail. If that is the case the total voltage between the positive and negative supply rails will exceed the absolute maximum allowable for the TLE2141 (44 volts).
EDIT: I found photos of what I believe to be the same board and confirmed that the op amp positive supply pins are all connected to the unregulated DC at the main filter capacitor. I couldn't see enough detail to really confirm the -5V supply, but that's what it looks like.
If the voltage is too high there is no easy solution. There are very few op amps that will run at greater than 44 volts. They do exist, but there isn't a lot of choice. If an amp is being used to drive an emitter follower power stage, which is quite likely, the maximum output voltage you'll get from the supply would be a few volts less than the positive supply voltage for the amp, so regulating the amp's power supply will also limit the output voltage you can get.
If your transformer has a centre-tapped secondary, I would suggest trying to get the regulator board working using just half of the winding (i.e. centre tap to one end; leave the other end open). This will limit the voltage you'll be able to get but get the unregulated voltage down to where everything should be safe from overvoltage damage. Again, measure the power supply voltages for the op amps. If they are more than 22 volts between the [+] and [-] rails when using half the transformer voltage, you simply can't use the full winding without modifications to the board. Those mods are probably beyond what you can figure out how to do if you only have basic knowledge.
Thank you for the explanation! Yes it seems this 30V transformer was a bit of an overkill for this design. Sadly it doesnt have a center tap. I will try to source another transformer with lower voltage and continue testing .
@@d614gakadoug9 Here in UK we have 240v mains supply, my supply is usually around 245volts, so if using Chinese transformers designed for 220volts output voltage off-load will be much higher than nominal voltage. I used two 18-volt transformers as I didn't have centre-tapped one. Output voltage was OK up to 25-volts, but current limiting didn't work as supply to op-amps was too low. Shunting series resistor in supply to op-amps restored op-amp voltage to near normal. Tried reverse engineering circuit, but was not easy, but found a circuit on Mile Kokatov, Z33T, webpage together with excellent article with suggested mods. For low currents you can use one non-center-tapped transformer with two diodes connected as in voltage-doubler circuit, fed to the 3-terminal AC-input. Positive end of one diode to one side of 24v input and negative of other to other side of 24v input. The remaining connection of the transformer goes to the center-tap of the input.
Hello. The problem was the short that was mistakenly made when regulator board touch the heatsink pipe, which is from copper. One must be more cautious.
Salut. Daca pun 3 sau 4 tranzistori in paralel, sursa poate duce 8..10Amperi?
It be amazing if you make "upgrade" to the kit so the volt and amp can be adjusted slowly +- 0.1 v not jumping like the default
It just needs 10-turn pots to accomplish this. I have done this.
So i just need to change the included potentiometer with the 10 turn right?, and what are the pots value
@@raihanrizki1803 10k
@@raihanrizki1803 value isn't so important, you can go with same as original (10k if I recall correctly) but anything will work.
@@raihanrizki1803 they usually are 10K or 1K. Sometimes one 10K and the other 1K
Belle vidéo, j'ai aussi réalisé cette alimentation, j'ai appris des choses grâce à vous, merci !
Buna dimineata! Can you tell me more about the transformer? How many Watts or Amps does it have? I like this project, but I am afraid If I put it in a case, the transformer will be the first to burn. That and adding a breaker on the output so it clicks instead of blowing a laptop up LOL.
Mulțumesc!
Sorin be careful, warming up a heatpipe that much can very easily make it explode.
And if it doesnt explode, it loses some of the ability to move heat to the heatsink
Hello sorin... is that working 30volts ac transformer without change the value of resistor?
I've just bought one and it doesn't reach 30V.......it goes maximum to 26V. Any idea what could be wrong?
Is it possible to use 12volt transformer? The output voltage is not matter.. anyone can answer this? Thanks
Can we build Darlington circuit using these two transistors instead of parallel?
Thank you Sorin
that would give you more gain but you don't need that (opamp can provide more than enough gate current).
Haha, time flies. I remember it like it was yesterday.
17:50 MTGA movement motto "Ok lets use proper calibrated wire to Make Track Great Again ..."
Sorin is my favorite influencer in the repair industry. Hi really love what is he doing
on that lil 5v board, the cap on the end blew... magic smoke 🚬 .. i watched it frame by frame...
This smoll green 5v-12v bastards used a lot in fpv drones, for various purposes, powering a gimbals, eleron/rudder servo machines, ets. And them diying a lot for millions reasons, me and friend crash a lot rc planes before start using good quality dc-dc converters :)
But at least we have a lessons :)
the trace wants for 5A 110mil end emitter 0.1ohm resistor
Properly calibrated fire extinguisher in order sorin. I use one myself. And remember, no capacitor, no shorted capacitor. 😂
Sorin, after hour from you published that video there is not in stock in Amazon. Your audience is extremely loyal
They are not sold out, but probably Amazon have restriction based on the zone/continent/country. Check aliexpress or search on your amazon/ebay
great video and great cheap supply i have it too 😉
12:39 minutes I think you didn't know the maximum voltage input of your mini step down dc to dc converter, which is connected to your cooling fan ,
i saw that smd filter capacitor burn out, as I've zoom in the video, 😅 you mishandled it don't you, better luck nxt must check your module's capacity input before connecting into the input supply 😢
need to lower the value of the current sense resistor and fit a higher wattage one too!
How can we ad the relay for clicking effect of short circuit? Same question as @mendiarapi
مرحبا سورين لقد صنعت مصدر الطاقة هذا وظلت مضخمات التشغيل 24v kouini transistors
Hello,
Question, I didn't fully understand your toroidal transformer.
You mentioned that it's small one. And it was still capable of outputting 5.3A?
What is the rating of your toroidal transformer? Was it rated to output 5.3A?
I ask this because I am interested in the transformer's point of view. If the transformer is rated for max "lets assume" 3A secondary max current. And you squize out 5.3A that means it was overheating and it could be destroyed if you would run it a bit longer?
And on other hand... if toroidal transformer would be rated for max secondary current output of "lets assume" 8A. Also the Linear Adjustable Power Supply could see the 8A instead of 5.3A right? Or am I wrong?
Very interesting and good video. In this video
Best regards,
P.S.:
I don't quite have this part of electricity figured out at the moment. But I would like to clear it up a little. Because I want to make a simple audio amplifier (with TDA7294V) in the future and i don't know which toroidal transformer to buy regarding the needed output currents... not destroy the transformer if amplifier would need alot of current...
the fuck are u sayin
go learn basic circuit
voltage and current
and power
If your transformer can't handle the current drawn, the voltage will drop severely and its core will overheat , which can sometimes lead to melting( in severe cases). If your transformer can handle more than the current which the supply can draw, you will have a more stable voltage output but you will not get more amps on the supply output. As for the TDA7294 amplifier, If you make it stereo, you will need a transformer with a voltage of 2X25VAC and about 350VA.(You will have 2x35,25VDC after rectifying and filtering) You must use only 8 ohm speakers when you use a +/- 35V supply!
Determining the current rating for a transformer can be quite complex.
Usually transformers are rated for RMS current. When you rectify and capacitively filter the output of a transformer, the RMS current from the transformer will be greater than the average current you draw on the DC side. The higher the capacitance you use, the higher the ratio of RMS current to average current. (What happens is that current only flows if the instantaneous voltage of the transformer secondary is greater than the voltage on the capacitor. That means that the current typically only flows for a small fraction of each half cycle, but the amount of current is much larger than the average DC. The RMS value of those current pulses can be very high.)
Audio makes things more complicated because you very rarely continuously draw full power from the power supply. Usually with audio you can get away with using a transformer with lower current rating than you might for a bench supply that would continuously deliver. It is perfectly OK to draw more than rated current from a transformer as long as the long-term current is within the rating and the over current isn't drawn for very long. What you're really trying to do is keep the peak temperature of the copper windings within allowable limits. Remember that power dissipation in a resistor is proportional to the square of the current though it. The windings have resistance. If you draw 150% of rated current the resistive losses in the windings will be 1.5² or 2.25 times what they would be at 100% of rated current. If you draw 70% of rated current the resistive losses in the winding would be 0.7² or about half of what they'd be at 100%.
Some manufacturers of transformers publish applications information to help you determine what you should use.
@@Atelierul29
Thank you very much for your reply and help (I replied to your comment I think the second day after posting but I don't know why it doesn't show it. I'll reply again).
As you guessed I want to make a stereo TDA7294 audio amplifier. You mentioned that for the TDA7294 I would need 2x25V AC which would eventually come out to 2x35,25V. You mentioned that you recommend 350VA. I looked at what options I have to choose from regarding transformers and I found. Option 1: MULTICOMP PRO VTX-146-300-125 which can deliver max 6A current (Not as expencive as 500VA)
I looked at the datasheet of the TDA7294 Audio Amplifier and I see that it has a output Peak-current of 10A. So would I need a more powerful transformer? let's say Option 2: MULTICOMP PRO VTX-146-500-125 (To me little too expensive) which can deliver 10A of current. And since I need 2x IC TDA7294 to make a stereo then I would probably need a 500VA transformer?
Yes, it's true. On very, very rare occasions I will have the volume up to max. And it is probably very difficult to get to a peak-current of 10A and maybe from that we can conclude that a 500VA(max.10A) or even a 300VA(max. 6A) transformer would be sufficient?
Also, may I ask why I should only use 8ohm speakers? I currently have 6ohm speakers at home which I would like to continue using (this would save a little on cost of this wanting DIY project).
I know that if I have 6ohm speakers they will require more current from the amplifier which probably the 300VA transformer would not handle. But how much current change are we talking about? I have no idea. realy rough assumption - would 8ohm speakers need 6A and 6ohm speaker 8A?
@@d614gakadoug9 Thank you very much also for your reply and clarification. It was very helpful. And I understand what you wanted to say. However, it is still interesting to me that such a small toroidal transformer in the video can deliver 5.3A without the transformer heating up. For example, I am now looking at (from a previous reply) a MULTICOMP PRO VTX-146-300-125 transformer which weighs 3kg and has the capability of delivering 6A current. Interesting, I have no concept yet why such a small transformer could deliver such a current without troubles.
I wonder if that kind of power supply can be used as an injection tool, I need one