Great video, as usual! One thing people might want to consider building this, the Tab of the 7812 (the part that you screw to the heat sink) is connected to the ground pin. On the 7912 it is connected to the input pin. I wish I could say I didn’t learn this the hard (read hot) way..
Supertyp there are some special parts available for isolating the heatsink from the tab of the regulator, but these also prevent some conducting of heat. Most of the time I don’t connect the heatsink of the negative regulator to anything on the PCB, if it is mounted there.
Hi, I’m a mechanical engineer working in the power electronics field and have a suggestion on how to electrically isolate the device from the heat sink while minimizing the thermal impact. The best way I have found is to use Kapton tape (polyimide film) which is an electrical insulator with a very high temperature rating. As long as a single tape layer is used the temperature increase will be negligible. I’d lay down a single strip of Kapton tape on the heat sink, then burnish it (rub it) really well. Rubbing it with a hard edge such as a credit card will make sure any air bubbles are removed and you get the best adhesion possible. Don’t use the corner of the credit card since it could apply uneven pressure and put indentations into the tape. You want as smooth a surface as possible, so start at the middle of the tape strip and rub outward towards one end, then repeat for the other end. Gradually apply pressure when starting in the middle each time. Start the final few strokes near one end and finish towards the other to make sure the middle section is evened out. (Who knew applying tape could be so exacting?! Lol.) Once the tape is applied just mount the device as usual, including using thermal grease between the device and the tape to fill any remaining air gaps. It’s really hard to screw this up, short of leaving a huge air bubble right under the device. Good luck! Edit: I forgot to mention that Kapton tape is semi transparent, which makes spotting air bubbles really easy. When you burnish the tape you’ll see a distinctive darkening underneath it as the adhesive wets the heat sink surface and air bubbles are driven out.
You can also directly mount to an anodized aluminum surface, which is not electrically conductive. The only caveat there is to be on the lookout for fresh scratches or abrasions exposing raw, conductive aluminum.
At 16:36 To calculate capacitance or ripple, there is a standard equation: Charge = VC = It. That means the current times the time for which it is drawn is equal to the capacitance times the drop in voltage that results. In the UK, we have 50Hz, so the time between one positive peak and the next is 20ms. In the US, that is 60Hz and 17ms. That is the maximum time that the capacitors are needed to supply current. If we draw 1A for 20ms, that must be equal to the capacitance times the voltage drop in that time (the ripple voltage). With 3 x 4700μF, the ripple V = 1A * 20ms / 14100μF = 1.4 V That means the 17V peak of the rectified 12VAC will drop to no less than 15.6V, allowing enough headroom for the 7812 to operate.
Darn. I just explained the same thing before I read your comment. Note: C(I will buy) > C(I need) / (1 - percentage) the typical +80% -20$ cheap capacitor needs to be scaled up by 1/(1-20%) = 1/(1-0.2)
Hearing “ground” described as a “reference” is the one thing I needed to finally understand fully what it referred to. Not sure why nobody else had before.
(1) "big capacitors" (electrolytic capacitors) have poor characteristics to the harmonics of a rectified sine wave. (2) "small capacitors" (mylar capacitors) are used to filter these harmonics: 0.47uf mylar is cheaper and suitable: to be effective mount close to the L7812 regulator using short leads. (3) L7912 regulator : use mica wafer to insulate metal TAB from grounded heat sink : the TAB is internally connected to negative unregulated voltage.
Quick note: I have two different brands of LM7812 on hand. With the ST part the 1uf cap on the output worked fine but on the other brand I saw a sawtooth in the output. Reducing the capacitance to 0.1uf smoothed it out. I need to find the datasheet for those parts but I guess keep in mind that not all 7812s are the same and check your datasheets. I wouldn't not have been able to see that noise without an oscilloscope.
I've seen some datasheets that specify a MAXIMUM capacitance that you can put on the output side, and this does vary by manufacturer. At least one manufacturer provides a formula for determining the size capacitor you should use. The same goes for the very similar LM317 regulators, which are used when you want to use the same part for a number of different voltages, or even a variable voltage. It just requires two additional resistors that determine the output voltage. That "maximum capacitance" can be a problem, because in many cases, the circuits you are operating from the power supply have additional capacitors added to their power inputs. But since that sawtooth you see is caused by the regulator going into oscillation, this is also affected by the inductance between the regulator and the capacitor, and in the case of modules being powered from a power supply, just the wire connecting them together usually has enough inductance to eliminate the oscillation.
@@BrightBlueJim This is an old post. If you build this I think there's actually too much reserve capacitance and it can kill your AC power supply due to the inrush. There are better options.
@@justovision Nonsense. AC wall warts are just transformers, and nothing else. You'd have to put a LOT of capacitance on it to kill the wall wart, and even then, the rectifiers would probably go first. A lot of commercial audio products use pretty much exactly this kind of supply to get bipolar power to run op amps.
@@justovision- NO, because what is supplying the AC is a transformer. At high current, the voltage sags. So when it starts up, the capacitors form an almost short circuit so the transformer outputs it's rated Current and a very low voltage. As the capacitors charge (perhaps 1 second) the current decreases and the voltage increases. Once the capacitors are charged, the current drawn follows the load. You could add a low resistance high wattage resistor as a "current limiter" however the transformer's output windings and the cables from the wall wart to the PSU will do the same thing in real world terms. It might be a consideration for a PCB mounted transformer and 10's of Amps, but for simple low power stuff it is not an issue.
I'm loving these videos! One thing I would change is the rectifier, you could use a full-wave rectifier at the transformer output so you don't need those giant capacitors to hold the signal for so long.
Normally, you would be correct. But in this case, the circuit that he is using is a voltage doubler. So, you can build a doubler with a bridge rectifier.
Just built a power supply for my modular synth. It's very very simple. There are two 12v wall warts. They plug into a panel with a switch, LED indicators, and a cable running to the bus board. The positive of one connects to the negative of the other, to create a common 0v reference. I think it works fine but I'm leaving things simple so I can improve the power supply in the future.
@@MoritzKlein0 English was German at one time until it was tainted :). Seriously though, there is a lot of crossover between the languages. When I was in HS my science teacher had a German pen pal (this was about 35 years ago :P) and one day I was reading over his shoulder and I actually could understand a lot of the letter! My science teacher was impressed. I guess he thought I was some kind of language savant. I am a software engineer, so languages are near and dear to me, but no, it's just because there are a lot of similarities and I noticed the pattern.
Hello Moritz! Thanks to you I've managed to build an adjustable dual rail psu using lm317 and lm337 with shottky diodes and small trimpots to adjust plus and minus of psu to a desired value. I had no real reason using shottky diodes except their small voltage drop. I have thought that it must provide a broader voltage adjustment range thanks to small voltage drop specially when transformer maximum output voltage is barely sufficient. I also experimented with cold lazer toner transfer to make a small and accurate pcb using alcohol+acetone mixture. I recommend.
As an electrical engineer, I WISH I had this channel while I was learning This is better explained and visualized than most classes I had to power through hahaha
I would strongly recommend putting two bleeder resistors in parallel with the electrolytic capacitors. Lower resistance for faster discharge, but a 1W 220R resistor would be good for about 5seconds of discharge time to less than 2 volts. The amount of capacitance can pack quite the amount of current in short circuit.
Thank you so much for the incredible work in your videos, this kind and level of pedagogy is the stuff of the future to me! I'm just blown away by the clarity/quality of your explanations, this is pure light in the darkness! Deep respect from the bottom of my heart man!
OMG I Made this, video on in the background, and still got the polarity of the capacitors wrong. At the -12V the polarity is reverse! Yes one 4700uF capacitor just blew up in my face. No one was injured..my ears are still ringing and my girlfriend is pretty mad.
This is a great design for small scales, but linear regulators get really inefficient when they have to push out several amps. I would recommend going switching anyway (ICL7660 to go from +12v to -12v), but smoothing it out by either 1). Making the voltage a few volts too high and sending it into a linear regulator for less noise, or 2). Using a circuit called a capacitance multiplier (transistor buffered RC filter) to filter out the noise
Your tutorial videos are the best I've ever/seen, and I have read watched a LOT! I've learned 8 different programming languages the entire Arduino world ect... Seriously Ive read/watched an unbelievable amount of tutorials and your series is honestly the best I've ever seen. Thank you
You could use a powerful op Amp (TDA2030) as a buffer and a 50% voltage divider at input to get the middle voltage level at the output of an SMPS. Still the high frequency noise will be there but it would work to make a 6-0-6 from a 12v SMPS.
Hi Moritz ! Thank you this video ! My power supply is 12V AC 1000mA, what 's the thermal resistance I need for the heatsinks please ? What's yours for example ? And if i want to add a fuse after the power connector, I have to use a 1 amp fuse ? Thanks 😊
Thank you for the educational video. This is a very curious design, I would never had though a single diode rectifier could be useful for anything. The most unique feature of this design, apart from its simplicity, is that you get +/-12 V out of just 12 V AC - the output voltage doesn't get halved like in artificial neutral point designs.
Great video, I love your contant and have build some of your stuff allready, including this power supply. But i think my AC to Av wall wart broke so i want to buy a new one. Which Current would you suggest? before i used 1500mA
depends on how much current you want to draw from your power supply. the regulators are able to handle 1.5 A each. but they‘re fine with supplying less.
When it comes to calculating capacitor sizes for linear power supplies, I really like this calculator: www.changpuak.ch/electronics/power_supply_design.php It lets you put in your transformer voltages, load, and capacitor sizes, and shows you a graph of the resulting ripple. It's been really handy for me in the past.
Thank you so much for that link!! I've been struggling for the last few days, blowing up the rectifier diodes (solved by adding a 4W 180Ohm resistor in series with the transformer output) and today blowing the 1A fuse on the transformer primary (must have drawn >230W of power!). Well now I know the culprit - way too much capacitance. 6 x 4700uF = 28200uF and according to that calculator, the worst case inrush current is nearly 40A (at 18.2V). Need to revisit the design and this website will help a lot. Thanks again :)
You can work out how much capacitance you need fairly easily, by making use of the fact that the rate of change of voltage across a capacitor (in volts per second) is equal to the current flowing in or out of it (in amps) divided by its capacitance (in farads). Knowing the maximum current your supply needs to be able to deliver, you can calculate how much the voltage will fall between one peak and the next for a given capacitance. In your case the maximum current is 1A, and for 50Hz mains the time between peaks is 20ms, so to ensure the ripple is no more than 2V you would need at least 1A * 20ms / 2V = 10mF = 10,000uF.
The 12V Wall Wart that you are using very likely has not much more inside the case than a 12V transformer. Meaning, a bare transformer could be used, with a proper project housing and precautions. Your suggestion to use a Wall Wart is good, because you are teaching people with less knowledge and you want to keep them safe. So, the ready-made Wart housing, wall plug pins and cable is a really good way to go. But, for folks that do not have access, or the financial ability, to buy a Wall Wart, they might recycle a bare transformer from a broken device. Just get some help with doing that from a knowledgeable person, so that you can stay safe.
Im really new to this. Where do you run the ground cable from this power supply? I see where you connected for the positive and negative rails but im lose on where the ground runs from.
You have one lead from the "wall wart" that has diodes hooked to it. You have one lead from the "wall wart" with no diodes hooked to it. This "no diodes" lead is your "nominal ground".
Brilliant as usual. The addition of the 1uF capacitor is often forgotten and, most of my 7805 based power supplies don't have one. Also, the capacitor on the output is often thought of as optional. I have made a number of them where I left the output capacitor out to save space and it worked fine... Until it didn't!!. I learned my lesson after that and went to the datasheet where it was clearly stated that there must be a capacitor on the output. If this video was around when I learned this lesson all those years ago, I would not have had to learn the hard way. What I really like about this video is that it covers all of the best practices for design and cuts no corners. Another great video packed with useful information.
i've been terrified to burn my house down with a power supply unit for the last year, and have been sitting on components, not doing anything with them. I came back to this to reflect on if i should get over it, and the line 0:51 to the point of scaling down the voltages......... why was i scared to do this? I'm already working with the right voltages that i am comfortable with for the rest of the projects from the plug itself, this PSU just makes that power stable and usable... if it blows, it'll be no worse than any other magic smoke we come across!
This vid and channel is a gold mind for what im trying to learn. Shame I dont have an oscilloscope, but I should be able to follow ur instructions just fine I just wont be able to check the actual wave forms rn.
Just one comment on a thing you said at the end of the video... I'm not sure the LM7912 has a built-in protection diode. A diode may be needed if the output capacitance is large enough -- see Fig. 2 of www.ti.com/lit/ds/symlink/lm79.pdf Also, see this discussion on the TI support forum: e2e.ti.com/support/power-management/f/196/t/566228?LM7912-Ext-Diode-for-protection
Hey Moritz, where does the other side of the AC transformer connect to? I did not see it in your schematic but it looks like in your breadboard layout it is connected to the ground rail
You are making all the common mistakes: 1) Calling your 0V "GND". 2) Using the mains PE symbol for 0V when you don't have one, you should use the inverted triangle symbol for signal common. These are international standards, not personal preferences. 3) Not calculating the voltage drops and tolerances. You can't make a +12Vdc power rail from a 12Vac transformer. It will drop out of regulation as more current is drawn. 4) Not calculating the power dissipated by the regulator and using a heatsink that is too small. A heatsink is not a magic device that sinks heat, it has to get rid of it as fast as it comes in. A finned heatsink needs an airflow along the fins and the air has to exit the box it is in, otherwise you have only built a thermally unstable oven. 5) A synthesizer is not a safety Class II device because the user touches bare metal parts (the patch cables) that could become live under fault conditions. You cannot run a Class I device from a Class II PSU. The system 0V should be connected to mains PE, that makes it grounded but it is still not "GND". Most modular synthesizer PSUs make all the same mistakes which is why users have so many problems.
I pretty much agree, these videos are good info if you are already educated in someway, but they are so dumbed down (in a good way), that the lay person would likely commit grave errors in design. However, regarding the 12Vac transformer having not much headroom, is that really the case? Afaik the 12Vac is the rms rating, then the + or - amplitude would be 12×1.414 ≈ 17V >> than the 14V min required by the 7812. Or did I miss something here? Best regards
@@SuperGuirro hello, yes, you missed three things: 1) Most transformers are designed for 115/230Vac primary voltages, but in reality that varies +/-10%. In Europe the voltage is really 220Vac and in the UK it is really 240Vac, the tolerances have just been fudged in the name of "harmonisation". For real world use you have to design for -10% minimum and +10% maximum, the latter has more waste heat. 2) The secondary rating is not Watts it is VA which is the maximum output voltage times the maximum current, but you don't get both at once. This is where you have to use the output regulation figure to derate the output. 3) You have to allow for the diode voltages drops in the bridge rectifier and the fact that current is only drawn for a fraction of the mains cycle. If you take all these factors into account a 12Vac transformer will not work in all circumstances, but a 15Vac one will.
@@hintoninstruments2369 PS: do you also know where these wall power supplies of 15VAC are available? Last time I checked no one was selling them (EU plug). Regards.
@@SuperGuirro I don't recommend using this type of adapter because they do not pass the PE through. A modular synthesizer is not a double insulated appliance and the PE should be connected to the power distribution 0V, rather than the PSU. People avoid doing this to evade certification expenses. but that just creates an unsafe device that will also give hum problems. You need a 3 pin IEC inlet to get PE to the system. See mistake 5) in my original comment.
Thank you so much for these videos! You have a rare and valuable gift, please keep it up. I will be using these videos to teach electronics to my kids, there is absolutely no way I could even come close to your teaching skills. Thank you!
Fantastic Videos! I'm currently planning to build my own synth, and I'm using your videos as guideline. As I have never built anything with electronics, I have one noobie question regarding the power supply: In your other video, you recommend combining two 9V batteries. In theory, would this also be possible by using two separate 12V DC PSUs? I have a hard time getting a decent AC/AC wall wart whereas 12V AC/DC PSUs are cheap and widely available. Frankly, I would also rather not build a PSU myself at all if possible, since I'm not confident in my skills yet (although your video makes it look very easy).
Very nice as usual, I just regret you didn't talk about the specs of the 7812/7912, the current they can drive. What type of transformator we can use, how many VA ? what happens if you try to drive too much current out of the 7812/7912 ? is it usefull to also generate +- 5 V in eurorack ?
16:48 Computing the capacitor is not hard. Here is how to do it. Assume the capacitor is fully charged at the peak of the sine wave call this the V1 Find the voltage that is the lowest the LM7812 will like call this V2 Assume the mains is 50Hz so the time is 1/50th of a second call this T The current is I. How much charge you took out of the capacitor is I*T = 1A/50Hz = Q (V1-V2) = Q/C Do some math C=Q/(V2-V1) Yes, this is a bit inaccurate but the error is smaller than the 20% on a capacitor. Remember to make your nominal capacitor big enough that the one you actually get will be good enough. C(I will buy) > C(nominal) / (1 - percentage)
well the 7812 can push out 1A at max, and the 7912 1.5A. now it depends on how much current your modules draw, but with my PSU I'm powering around 7 or 8 modules. (keep in mind that some/all of them are shoddily designed and use more current than they'd really need to.)
@@MoritzKlein0 amps is a measure of current flow. Watts is a unit of power. The TO-220 package fixed regulators are rated for a max output of 15W. In the TO-3 package they are good for 20W Amps is the same though. Go figure. What you need to do is look at how professionally made things are constructed. Take a PC for example. They have a PSU that supplies rail voltage and then regulation happens for each circuit block (VRMs). Eventually you'll see the light and come around. With electronics you build a lot of power supplies.
@@1pcfred Note that the wall wart suggested also only puts out 1A @ 12VAC; I suspect this will be the limiting factor long before the linear regulators are, due to losses to heat in the vregs and passives. If somebody wants to scale up to a massive rack, it'd be a good idea to either get a professional PSU (something from meanwell, maybe?) or redesign this PSU to handle the higher load. That said, the eurorack community assures me that cross-patching between racks doesn't cause issues as the ground voltages get tied together, so building one of these for every 10 or so modules might also be an option.
@@oasntet powering large projects is a bit of a trick. Expecting to do it all from one regulated source is a big ask. Trying to do it that way you're setting yourself up for trouble. Local regulation is a more realistic strategy. With regulators so cheap and easy to use today it's the sensible way to go. When you look at pro designs they may have a half a dozen regulators on one circuit board. They use overkill to get it done. You have to be comfortable with the complexity when you're dealing with complexity. Otherwise things can get too complicated.
I'm a professional and I don't build a PSU completely from scratch. while I know what to do and what not to do to not get injured or worse, others that might touch/access the connected devices most likely do not. So to safeguard the non-professionals, anything a consumers/lay person can get in contact with I fall back to be safe and use e.g. prefabricated tested and rated transformer coils with the integrated safeguards against touching mains carrying circuits.
Questtion, since my 1N4007 rectifier diode does not react like in the "Rectification in practice" cahpter: after a short while cuttingthe wave right, the wavemountains drop to no current in my oscilloscope (doublechecked: orientation of the diode, and tested it with a multimeter, seems to work properly). What am I doing wrong? Thank you for help!
Uh, I made a bitter mistake: From checking the AC my Oscilloscope was on "AC". In order to see the right graph ("mountains with cut valleys") I had to switch oscilloscope to "DC"...
Why not use one big full Bridge rectifier rather than two separate half Bridge circuits. If you're positive rail has a lot more draw than your negative it's only going to be able to deliver a certain amount of power versus potentially all the power from the sine wave. Isn't that the case? Also you have the small fast-acting capacitors before and after the regulator. Why wouldn't you also want some of the bigger capacitors after the regulator as well?
this might be the stupidest question of all, but assuming you would leave this on a breadboard, how would this turn on a module? where would it plug in to?
If it plugs into a wall socket I'm not touching it. I've got a variable power supply but I rarely touch it. Those voltages and currents scare me and I know I don't know enough to start fxxing with this stuff. Interesting watch though. Rule number one, even with batteries, REMOVE POWER from the circuit before you touch it and be careful of things like capacitors and inductors. Have fun, don't kill yourself :)
two reasons: first, the wallwart‘s peaks are around 15, not 12V. second, it’s good practice to use caps that can handle at least double the voltage since they will last longer that way.
These are fantastic videos - I've been learning "modular" in Reason for years and I've gotten serious this year about getting an analog setup going. I have components, a couple breadboards and an Arduino from taking electrical engineering in college, even though I didn't go very far in it. I recently got the idea of adding a breadboard to my prospective modular rack - initially I just wanted to use it for splitters/mergers and simple logic operations, rather than buying multiple $100 logic modules - but this channel is on another level. My goal when I started learning electrical was to make a synth, but other tutorials didn't really get through to me. I made a sine bass with Arduino, but doing it with ICs on a breadboard is what I was aiming for. I've seen other tutorials, but these go deep, they're clear and thorough and the devices are valuable and functional for music production, as opposed to a tutorial on a single isolated multipurpose component. I don't think I'm ready to mess with a diy power supply yet, but I'm definitely going to do the VCO VCF and Sequencer/Arp and have ordered the extra parts. So dope thanks for your time and effort!
watched the whole thing but all i could think was, why aren't we using a DC supply and generating AC? that's the one thing i miss from these videos, briefly surveying alternatives so the viewer has an idea of where the technique sits overall ("this is the more affordable, this is the more efficient, this option avails this," et c.) until this makes sense to me, it's valueless.
Thank you for all the information! I build a psu similar to this but was having what I considered substantial inaccuracy :11.82 v on the positive. But I see yours is with similar accuracy. Isn't this a problem later, when control voltages are used for oscillation frequency and what not?
Maybe anyone can help: I built the PSU, doublechecked everythin thrice... But: The negative rail stays at -11 V and the condensators of the negative rail are getting hot quickly, so that I do not dare to use the PSU or even leave it under power more than a minute. Nay halp or idea is appreciated, thanks in advance!
I don't know if the link changed but the Jameco (US) power supply link in the description has a 3.5mm jack not a barrel jack. Alternatives: www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=2197581&productId=2197581 and www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=2227604&productId=2227604 (Only difference I can see is size of barrel jacks which is a completely different annoyance)
Is it possible to use a 8,5A voltage with 3 or 4 of those using high current resistors like those 5W ones they sell at Segor's`to "spread" the current between the rectifier-capacitor-array-modules??
This is not a good design. The transformer is designed to have equal current loads on both parts of the cycle. Unequal loading can cause overheating or failure. Also the caps have to be very large to filter the half wave rectification. Much better is to use dc in and generate the neg 12 supply from the pos supply. There are -remade products that gen pos and neg 12 from one pos input.
I only have aluminum electrolytic 1uF capacitors at hand, is that an issue? I also have 100 nF ceramic. What's the better choice? Willing to build this now, not to place one more order and wait...
@@MoritzKlein0 Did it on breadboard, everything fine, just soldered on stripboard the positive side and I now get 18 volts... Any idea about what could be wrong?
I've never heard dual power supplies be explained so clearly and in so much detail. Thank you Moritz you help make these learning curves much more enjoyable!! I have a question though. Where does the ground go? (0 volts) as there's only the + and - 12v? I'm sure the answer is simple but I can't figure it out! Thanks!
@@sine0 I think you arbitrarily choose one of the wires from the wall wart to be ground/0v and treat the other like it is the source of the AC current. I think it's more intuitive if you look at the circuit diagram at 24:00 and imagine the ground connections on the bottom half of the diagram being flipped up to meet the ground connections from the top half in the middle. It looks a lot more like a rectifier when you view it that way. It reminds me of how we think of current as going from positive to negative even though it's negatively charged electrons moving in the opposite direction and you sort of accept that relatively it's the same thing.
Hi Moritz, I was thinking about creating my own modules and/or little standalone mixer and effect pedal. How do I get a dual power supply out of one dc supply like pedal power (9V) or USB Power. Do you got some ideas or knowledge sources I could look up?
Crazy amount of details but not boring and not enough! Excellent RUclipsrs are difficult to come by. Moritz, have you any experience with so-called 'laptop tingling'? For engineers like you would say it is actually capacitive coupling. Happens to all the small switching ones, transformerless, lethal, 2-prong, for mobile phones power supply. This is important as I get weird humming, buzzing, humming, and other noises besides that 'tingle'. The so-called 'audio transformer' 600 ohm : 600 ohm does not help. Maybe I am using inexpensive one. (Probably Chinese rubbish) There is no need for me to spend a lot of money because I am not doing anything professional. Only an electret microphone preamplifier. The only way I understand how to eliminate that is to either ground it to true ground/earth or hack the mini transformer inside and place a foil as Faraday shield. Hacking a transformer is impossible for me, and to most people. So, grounding it to earth is the best way. However, I lately learnt about "balanced" circuit using instrumentation amplifier. An instrumentation amplifier an eliminate some, if not all, of those noises, and it can easily be DIY with three operational amplifiers (I have NJM5532D / NE5532AP which I think superior to the common ua741, LM741, LM358 in terms of low internal noise).
Could I put the diode on the +12 side on the output past the cap (facing out) or does it NEED to bridge the voltage regulator like shown? If so, what is the difference?
one thing to note about AC current is that there is a "ground" wire. It's called the neutral wire and is used as a 0 volt reference. instead of a positive wire, AC current uses a "hot" wire which has all the voltage. To tie it back to your water analogy, the neutral wire is basically our ground wire because it stays at atmospheric pressure (a.k.a: ground or 0 volts), while the other hot wire rises and falls in pressure 50/60 times per second around the neutral wire, which creates the sine wave you see when hooking it up to an oscilloscope.
@@MoritzKlein0 Hi, have you found something yet? I've also been looking for an AC/AC wall wart but I'm finding it very difficult. Some people suggested buying a power bank but these tend to be rather pricy for my use...
What you said about how to connect the ground clip of the oscilloscope isn't totally right: you can connect it where you want because the output of the transformer is insulated from ground, otherwise you will destroy something (probably you oscilloscope). If you want to connect the oscilloscope with more liberty, you have to make sure that only one object could be connected to ground, because it will connect everything else when connected to other devices (usually, when possible, the oscilloscope is connected to ground to ensure a better noise immunity), otherwise the ground of the oscilloscope has to be connected to the ground (otherwise there will be a shortcircuit) and you also have to make sure tu avoid ground loops and other bad things
It has to do with what falls out of the design by accident. The process of making a chip makes lots of accidental diodes as you put down one bit of semiconductor next to another to make all the transistors you need to make the circuit. In the 7912 it just happens that one of them lands is a way the marketing department could call a "feature"
You can use class2 ac power supply cheap ones from behringer ( small mixer psu ,4 models witb different ma ) that cost about 10 euro , together with your schematic a cheap alternative that works
Hello, as said many times already: your videos are great! I am making this dual power supply but I have a curious issue: the positive rail is +12V as expected but at the negative rail I measure -6V. What am I doing wrong? Thank you.
Great video, as usual! One thing people might want to consider building this, the Tab of the 7812 (the part that you screw to the heat sink) is connected to the ground pin. On the 7912 it is connected to the input pin. I wish I could say I didn’t learn this the hard (read hot) way..
yes definitely! forgot to mention this. thanks for pointing it out!
What did you do? Simply isolate the heat sink from the 7912?
Supertyp there are some special parts available for isolating the heatsink from the tab of the regulator, but these also prevent some conducting of heat. Most of the time I don’t connect the heatsink of the negative regulator to anything on the PCB, if it is mounted there.
Hi, I’m a mechanical engineer working in the power electronics field and have a suggestion on how to electrically isolate the device from the heat sink while minimizing the thermal impact.
The best way I have found is to use Kapton tape (polyimide film) which is an electrical insulator with a very high temperature rating. As long as a single tape layer is used the temperature increase will be negligible.
I’d lay down a single strip of Kapton tape on the heat sink, then burnish it (rub it) really well. Rubbing it with a hard edge such as a credit card will make sure any air bubbles are removed and you get the best adhesion possible. Don’t use the corner of the credit card since it could apply uneven pressure and put indentations into the tape.
You want as smooth a surface as possible, so start at the middle of the tape strip and rub outward towards one end, then repeat for the other end. Gradually apply pressure when starting in the middle each time. Start the final few strokes near one end and finish towards the other to make sure the middle section is evened out. (Who knew applying tape could be so exacting?! Lol.)
Once the tape is applied just mount the device as usual, including using thermal grease between the device and the tape to fill any remaining air gaps. It’s really hard to screw this up, short of leaving a huge air bubble right under the device. Good luck!
Edit: I forgot to mention that Kapton tape is semi transparent, which makes spotting air bubbles really easy. When you burnish the tape you’ll see a distinctive darkening underneath it as the adhesive wets the heat sink surface and air bubbles are driven out.
You can also directly mount to an anodized aluminum surface, which is not electrically conductive. The only caveat there is to be on the lookout for fresh scratches or abrasions exposing raw, conductive aluminum.
At 16:36 To calculate capacitance or ripple, there is a standard equation: Charge = VC = It.
That means the current times the time for which it is drawn is equal to the capacitance times the drop in voltage that results.
In the UK, we have 50Hz, so the time between one positive peak and the next is 20ms. In the US, that is 60Hz and 17ms. That is the maximum time that the capacitors are needed to supply current.
If we draw 1A for 20ms, that must be equal to the capacitance times the voltage drop in that time (the ripple voltage). With 3 x 4700μF, the ripple V = 1A * 20ms / 14100μF = 1.4 V
That means the 17V peak of the rectified 12VAC will drop to no less than 15.6V, allowing enough headroom for the 7812 to operate.
Great help. Thanks
Darn. I just explained the same thing before I read your comment.
Note: C(I will buy) > C(I need) / (1 - percentage)
the typical +80% -20$ cheap capacitor needs to be scaled up by 1/(1-20%) = 1/(1-0.2)
But when you use a bridge rectifier, you have double frequency, so not 50 but 100 Hz.
@@igorzherebiatev5751 Indeed. So you use 10ms instead of 20 in the formula.
This guy really understands how to teach something. Keep up the awesome work!
Hearing “ground” described as a “reference” is the one thing I needed to finally understand fully what it referred to. Not sure why nobody else had before.
You are AMAZING, please don't stop uploading.
(1) "big capacitors" (electrolytic capacitors) have poor characteristics to the harmonics of a rectified sine wave.
(2) "small capacitors" (mylar capacitors) are used to filter these harmonics: 0.47uf mylar is cheaper and suitable: to be effective mount close to the L7812 regulator using short leads.
(3) L7912 regulator : use mica wafer to insulate metal TAB from grounded heat sink : the TAB is internally connected to negative unregulated voltage.
Quick note: I have two different brands of LM7812 on hand. With the ST part the 1uf cap on the output worked fine but on the other brand I saw a sawtooth in the output. Reducing the capacitance to 0.1uf smoothed it out. I need to find the datasheet for those parts but I guess keep in mind that not all 7812s are the same and check your datasheets. I wouldn't not have been able to see that noise without an oscilloscope.
I've seen some datasheets that specify a MAXIMUM capacitance that you can put on the output side, and this does vary by manufacturer. At least one manufacturer provides a formula for determining the size capacitor you should use.
The same goes for the very similar LM317 regulators, which are used when you want to use the same part for a number of different voltages, or even a variable voltage. It just requires two additional resistors that determine the output voltage.
That "maximum capacitance" can be a problem, because in many cases, the circuits you are operating from the power supply have additional capacitors added to their power inputs. But since that sawtooth you see is caused by the regulator going into oscillation, this is also affected by the inductance between the regulator and the capacitor, and in the case of modules being powered from a power supply, just the wire connecting them together usually has enough inductance to eliminate the oscillation.
@@BrightBlueJim This is an old post. If you build this I think there's actually too much reserve capacitance and it can kill your AC power supply due to the inrush. There are better options.
@@justovision Nonsense. AC wall warts are just transformers, and nothing else. You'd have to put a LOT of capacitance on it to kill the wall wart, and even then, the rectifiers would probably go first. A lot of commercial audio products use pretty much exactly this kind of supply to get bipolar power to run op amps.
@@justovision- NO, because what is supplying the AC is a transformer. At high current, the voltage sags. So when it starts up, the capacitors form an almost short circuit so the transformer outputs it's rated Current and a very low voltage. As the capacitors charge (perhaps 1 second) the current decreases and the voltage increases. Once the capacitors are charged, the current drawn follows the load.
You could add a low resistance high wattage resistor as a "current limiter" however the transformer's output windings and the cables from the wall wart to the PSU will do the same thing in real world terms. It might be a consideration for a PCB mounted transformer and 10's of Amps, but for simple low power stuff it is not an issue.
I'm loving these videos! One thing I would change is the rectifier, you could use a full-wave rectifier at the transformer output so you don't need those giant capacitors to hold the signal for so long.
probably a good idea!
came here to say that. i kept expecting him to switch the diode to full bridge
From what I understand, if you were to use a full bridge in this scenario, you'd end up with +12V and 0V, and no third voltage level
Medi from elektroboom would recommend this too
Normally, you would be correct. But in this case, the circuit that he is using is a voltage doubler. So, you can build a doubler with a bridge rectifier.
Just built a power supply for my modular synth. It's very very simple. There are two 12v wall warts. They plug into a panel with a switch, LED indicators, and a cable running to the bus board. The positive of one connects to the negative of the other, to create a common 0v reference. I think it works fine but I'm leaving things simple so I can improve the power supply in the future.
One small tip. The first C in the word ceramic is a soft C so it is pronounced as an S! Imagine it is a knight called Sir Ramick. ;-)
can’t hide my german descent forever i guess!
@@MoritzKlein0 Your English skills are great - it's just our language that is inconsistent. Sorry about that.
In german it's spelled with a k.
Before he was knighted he was just a young ramic
@@MoritzKlein0 English was German at one time until it was tainted :). Seriously though, there is a lot of crossover between the languages. When I was in HS my science teacher had a German pen pal (this was about 35 years ago :P) and one day I was reading over his shoulder and I actually could understand a lot of the letter! My science teacher was impressed. I guess he thought I was some kind of language savant. I am a software engineer, so languages are near and dear to me, but no, it's just because there are a lot of similarities and I noticed the pattern.
This is exactly what I was looking for! Thanks for not only sharing the information but making the effor to present it so clearly.
Hello Moritz! Thanks to you I've managed to build an adjustable dual rail psu using lm317 and lm337 with shottky diodes and small trimpots to adjust plus and minus of psu to a desired value. I had no real reason using shottky diodes except their small voltage drop. I have thought that it must provide a broader voltage adjustment range thanks to small voltage drop specially when transformer maximum output voltage is barely sufficient. I also experimented with cold lazer toner transfer to make a small and accurate pcb using alcohol+acetone mixture. I recommend.
I never understood physics behind electronics as much as I did after watching your videos!
As an electrical engineer, I WISH I had this channel while I was learning
This is better explained and visualized than most classes I had to power through hahaha
I would strongly recommend putting two bleeder resistors in parallel with the electrolytic capacitors. Lower resistance for faster discharge, but a 1W 220R resistor would be good for about 5seconds of discharge time to less than 2 volts. The amount of capacitance can pack quite the amount of current in short circuit.
but what for? 15V isn't gonna hurt anyone and it's constant power wasted
Absolutely unnecessary for such a low voltage. Continuously wasting half a watt also.
Thank you so much for the incredible work in your videos, this kind and level of pedagogy is the stuff of the future to me! I'm just blown away by the clarity/quality of your explanations, this is pure light in the darkness! Deep respect from the bottom of my heart man!
OMG I Made this, video on in the background, and still got the polarity of the capacitors wrong. At the -12V the polarity is reverse! Yes one 4700uF capacitor just blew up in my face. No one was injured..my ears are still ringing and my girlfriend is pretty mad.
This is a great design for small scales, but linear regulators get really inefficient when they have to push out several amps. I would recommend going switching anyway (ICL7660 to go from +12v to -12v), but smoothing it out by either
1). Making the voltage a few volts too high and sending it into a linear regulator for less noise, or
2). Using a circuit called a capacitance multiplier (transistor buffered RC filter) to filter out the noise
Your tutorial videos are the best I've ever/seen, and I have read watched a LOT! I've learned 8 different programming languages the entire Arduino world ect... Seriously Ive read/watched an unbelievable amount of tutorials and your series is honestly the best I've ever seen. Thank you
And OLD WALWART is a good choice, they are SAFE!!!!!
You could use a powerful op Amp (TDA2030) as a buffer and a 50% voltage divider at input to get the middle voltage level at the output of an SMPS. Still the high frequency noise will be there but it would work to make a 6-0-6 from a 12v SMPS.
Im so happy to see your new vids! So helpful
Hi Moritz ! Thank you this video !
My power supply is 12V AC 1000mA, what 's the thermal resistance I need for the heatsinks please ? What's yours for example ?
And if i want to add a fuse after the power connector, I have to use a 1 amp fuse ?
Thanks 😊
Thank you for the educational video. This is a very curious design, I would never had though a single diode rectifier could be useful for anything. The most unique feature of this design, apart from its simplicity, is that you get +/-12 V out of just 12 V AC - the output voltage doesn't get halved like in artificial neutral point designs.
Great video, I love your contant and have build some of your stuff allready, including this power supply. But i think my AC to Av wall wart broke so i want to buy a new one. Which Current would you suggest? before i used 1500mA
depends on how much current you want to draw from your power supply. the regulators are able to handle 1.5 A each. but they‘re fine with supplying less.
When it comes to calculating capacitor sizes for linear power supplies, I really like this calculator: www.changpuak.ch/electronics/power_supply_design.php It lets you put in your transformer voltages, load, and capacitor sizes, and shows you a graph of the resulting ripple. It's been really handy for me in the past.
Thank you so much for that link!! I've been struggling for the last few days, blowing up the rectifier diodes (solved by adding a 4W 180Ohm resistor in series with the transformer output) and today blowing the 1A fuse on the transformer primary (must have drawn >230W of power!). Well now I know the culprit - way too much capacitance. 6 x 4700uF = 28200uF and according to that calculator, the worst case inrush current is nearly 40A (at 18.2V). Need to revisit the design and this website will help a lot. Thanks again :)
Beautiful. The only problem with 78xx And 79xx ICs is that they do provide very little current out. About 1000 mA, if I remember well.
You can work out how much capacitance you need fairly easily, by making use of the fact that the rate of change of voltage across a capacitor (in volts per second) is equal to the current flowing in or out of it (in amps) divided by its capacitance (in farads). Knowing the maximum current your supply needs to be able to deliver, you can calculate how much the voltage will fall between one peak and the next for a given capacitance.
In your case the maximum current is 1A, and for 50Hz mains the time between peaks is 20ms, so to ensure the ripple is no more than 2V you would need at least 1A * 20ms / 2V = 10mF = 10,000uF.
thanks! If I'm correct, by this calculation, at 60hz you could realistically get away with one 4700uF cap per rail.
@@roccotuna- Um, nope. The capacitance isn't halved, it's basically 50/60th.
The 12V Wall Wart that you are using very likely has not much more inside the case than a 12V transformer. Meaning, a bare transformer could be used, with a proper project housing and precautions. Your suggestion to use a Wall Wart is good, because you are teaching people with less knowledge and you want to keep them safe. So, the ready-made Wart housing, wall plug pins and cable is a really good way to go. But, for folks that do not have access, or the financial ability, to buy a Wall Wart, they might recycle a bare transformer from a broken device. Just get some help with doing that from a knowledgeable person, so that you can stay safe.
Im really new to this. Where do you run the ground cable from this power supply? I see where you connected for the positive and negative rails but im lose on where the ground runs from.
You have one lead from the "wall wart" that has diodes hooked to it.
You have one lead from the "wall wart" with no diodes hooked to it.
This "no diodes" lead is your "nominal ground".
@@kensmith5694 Thank you!
Brilliant as usual. The addition of the 1uF capacitor is often forgotten and, most of my 7805 based power supplies don't have one. Also, the capacitor on the output is often thought of as optional. I have made a number of them where I left the output capacitor out to save space and it worked fine... Until it didn't!!. I learned my lesson after that and went to the datasheet where it was clearly stated that there must be a capacitor on the output. If this video was around when I learned this lesson all those years ago, I would not have had to learn the hard way. What I really like about this video is that it covers all of the best practices for design and cuts no corners. Another great video packed with useful information.
i've been terrified to burn my house down with a power supply unit for the last year, and have been sitting on components, not doing anything with them. I came back to this to reflect on if i should get over it, and the line 0:51 to the point of scaling down the voltages......... why was i scared to do this? I'm already working with the right voltages that i am comfortable with for the rest of the projects from the plug itself, this PSU just makes that power stable and usable... if it blows, it'll be no worse than any other magic smoke we come across!
This vid and channel is a gold mind for what im trying to learn. Shame I dont have an oscilloscope, but I should be able to follow ur instructions just fine I just wont be able to check the actual wave forms rn.
Just one comment on a thing you said at the end of the video... I'm not sure the LM7912 has a built-in protection diode. A diode may be needed if the output capacitance is large enough -- see Fig. 2 of www.ti.com/lit/ds/symlink/lm79.pdf Also, see this discussion on the TI support forum: e2e.ti.com/support/power-management/f/196/t/566228?LM7912-Ext-Diode-for-protection
Hey Moritz, where does the other side of the AC transformer connect to? I did not see it in your schematic but it looks like in your breadboard layout it is connected to the ground rail
you use one side for the half wave rectification (with the diodes, capacitors, voltage regulators) and the other strictly for ground.
You are making all the common mistakes:
1) Calling your 0V "GND".
2) Using the mains PE symbol for 0V when you don't have one, you should use the inverted triangle symbol for signal common. These are international standards, not personal preferences.
3) Not calculating the voltage drops and tolerances. You can't make a +12Vdc power rail from a 12Vac transformer. It will drop out of regulation as more current is drawn.
4) Not calculating the power dissipated by the regulator and using a heatsink that is too small. A heatsink is not a magic device that sinks heat, it has to get rid of it as fast as it comes in. A finned heatsink needs an airflow along the fins and the air has to exit the box it is in, otherwise you have only built a thermally unstable oven.
5) A synthesizer is not a safety Class II device because the user touches bare metal parts (the patch cables) that could become live under fault conditions. You cannot run a Class I device from a Class II PSU. The system 0V should be connected to mains PE, that makes it grounded but it is still not "GND".
Most modular synthesizer PSUs make all the same mistakes which is why users have so many problems.
I pretty much agree, these videos are good info if you are already educated in someway, but they are so dumbed down (in a good way), that the lay person would likely commit grave errors in design. However, regarding the 12Vac transformer having not much headroom, is that really the case? Afaik the 12Vac is the rms rating, then the + or - amplitude would be 12×1.414 ≈ 17V >> than the 14V min required by the 7812. Or did I miss something here?
Best regards
@@SuperGuirro hello, yes, you missed three things:
1) Most transformers are designed for 115/230Vac primary voltages, but in reality that varies +/-10%. In Europe the voltage is really 220Vac and in the UK it is really 240Vac, the tolerances have just been fudged in the name of "harmonisation". For real world use you have to design for -10% minimum and +10% maximum, the latter has more waste heat.
2) The secondary rating is not Watts it is VA which is the maximum output voltage times the maximum current, but you don't get both at once. This is where you have to use the output regulation figure to derate the output.
3) You have to allow for the diode voltages drops in the bridge rectifier and the fact that current is only drawn for a fraction of the mains cycle.
If you take all these factors into account a 12Vac transformer will not work in all circumstances, but a 15Vac one will.
@@hintoninstruments2369 Hey, really appreciated the in depth explanation! I will save this convo for future reference. Thank you very much!
@@hintoninstruments2369 PS: do you also know where these wall power supplies of 15VAC are available? Last time I checked no one was selling them (EU plug). Regards.
@@SuperGuirro I don't recommend using this type of adapter because they do not pass the PE through. A modular synthesizer is not a double insulated appliance and the PE should be connected to the power distribution 0V, rather than the PSU. People avoid doing this to evade certification expenses. but that just creates an unsafe device that will also give hum problems. You need a 3 pin IEC inlet to get PE to the system. See mistake 5) in my original comment.
Thank you so much for these videos! You have a rare and valuable gift, please keep it up. I will be using these videos to teach electronics to my kids, there is absolutely no way I could even come close to your teaching skills. Thank you!
Fantastic Videos! I'm currently planning to build my own synth, and I'm using your videos as guideline.
As I have never built anything with electronics, I have one noobie question regarding the power supply: In your other video, you recommend combining two 9V batteries. In theory, would this also be possible by using two separate 12V DC PSUs? I have a hard time getting a decent AC/AC wall wart whereas 12V AC/DC PSUs are cheap and widely available. Frankly, I would also rather not build a PSU myself at all if possible, since I'm not confident in my skills yet (although your video makes it look very easy).
Really great video. As someone who is just starting out and worried about electrocuting myself to death this has been a great help!
Very nice as usual, I just regret you didn't talk about the specs of the 7812/7912, the current they can drive. What type of transformator we can use, how many VA ? what happens if you try to drive too much current out of the 7812/7912 ? is it usefull to also generate +- 5 V in eurorack ?
Ceramic... "sir-am-ick"
Anyone another good source for ac to ac wall warts? The amazon one is not available, in reichelt i cannot find ac to ac ones. Thanks in advance!
Both a practical device I've been wanting, and perhaps the best illustrated analogy for current through diodes and caps I've seen.
Ok, now a video om how to add the +5v rail!
Btw awesome video.
Wouldn't that just require adding another "rail" with a voltage regulator with a 5V rating to the 12V input?
16:48 Computing the capacitor is not hard. Here is how to do it.
Assume the capacitor is fully charged at the peak of the sine wave call this the V1
Find the voltage that is the lowest the LM7812 will like call this V2
Assume the mains is 50Hz so the time is 1/50th of a second call this T
The current is I.
How much charge you took out of the capacitor is I*T = 1A/50Hz = Q
(V1-V2) = Q/C
Do some math
C=Q/(V2-V1)
Yes, this is a bit inaccurate but the error is smaller than the 20% on a capacitor.
Remember to make your nominal capacitor big enough that the one you actually get will be good enough.
C(I will buy) > C(nominal) / (1 - percentage)
Hi! You’re doing a great job! Thank you)
I have a question. Maybe it was mentioned but I missed it. How many modules you can power with such PSU?
well the 7812 can push out 1A at max, and the 7912 1.5A. now it depends on how much current your modules draw, but with my PSU I'm powering around 7 or 8 modules. (keep in mind that some/all of them are shoddily designed and use more current than they'd really need to.)
@@MoritzKlein0 amps is a measure of current flow. Watts is a unit of power. The TO-220 package fixed regulators are rated for a max output of 15W. In the TO-3 package they are good for 20W Amps is the same though. Go figure. What you need to do is look at how professionally made things are constructed. Take a PC for example. They have a PSU that supplies rail voltage and then regulation happens for each circuit block (VRMs). Eventually you'll see the light and come around. With electronics you build a lot of power supplies.
@@1pcfred Note that the wall wart suggested also only puts out 1A @ 12VAC; I suspect this will be the limiting factor long before the linear regulators are, due to losses to heat in the vregs and passives. If somebody wants to scale up to a massive rack, it'd be a good idea to either get a professional PSU (something from meanwell, maybe?) or redesign this PSU to handle the higher load. That said, the eurorack community assures me that cross-patching between racks doesn't cause issues as the ground voltages get tied together, so building one of these for every 10 or so modules might also be an option.
@@oasntet powering large projects is a bit of a trick. Expecting to do it all from one regulated source is a big ask. Trying to do it that way you're setting yourself up for trouble. Local regulation is a more realistic strategy. With regulators so cheap and easy to use today it's the sensible way to go. When you look at pro designs they may have a half a dozen regulators on one circuit board. They use overkill to get it done. You have to be comfortable with the complexity when you're dealing with complexity. Otherwise things can get too complicated.
I'm a professional and I don't build a PSU completely from scratch. while I know what to do and what not to do to not get injured or worse, others that might touch/access the connected devices most likely do not. So to safeguard the non-professionals, anything a consumers/lay person can get in contact with I fall back to be safe and use e.g. prefabricated tested and rated transformer coils with the integrated safeguards against touching mains carrying circuits.
Questtion, since my 1N4007 rectifier diode does not react like in the "Rectification in practice" cahpter: after a short while cuttingthe wave right, the wavemountains drop to no current in my oscilloscope (doublechecked: orientation of the diode, and tested it with a multimeter, seems to work properly). What am I doing wrong? Thank you for help!
Uh, I made a bitter mistake: From checking the AC my Oscilloscope was on "AC". In order to see the right graph ("mountains with cut valleys") I had to switch oscilloscope to "DC"...
Why not use one big full Bridge rectifier rather than two separate half Bridge circuits. If you're positive rail has a lot more draw than your negative it's only going to be able to deliver a certain amount of power versus potentially all the power from the sine wave. Isn't that the case?
Also you have the small fast-acting capacitors before and after the regulator. Why wouldn't you also want some of the bigger capacitors after the regulator as well?
3 cap da 4700 microfarad per un 7812 da 1 AMPER ???
Meglio uno da1000 micro e un 100 nano per l alta frequenza
Dammit, your videos are so good. Thank you so much for all that you do!
That heat sink looks crazy haha. Yet another helpful video, thanks!
Watch out, a 12v DC wallwart.will not work and most of them are AC
Because diode died
I have repaired countless power supplies, but never built one. This is most useful. Thank you.
this might be the stupidest question of all, but assuming you would leave this on a breadboard, how would this turn on a module? where would it plug in to?
I have never understood more how analog electronics worked better than after watching your videos. They are outstanding. Please make many more!!
If it plugs into a wall socket I'm not touching it. I've got a variable power supply but I rarely touch it. Those voltages and currents scare me and I know I don't know enough to start fxxing with this stuff. Interesting watch though. Rule number one, even with batteries, REMOVE POWER from the circuit before you touch it and be careful of things like capacitors and inductors. Have fun, don't kill yourself :)
why do we need 35V rated capacitors? Don't they charge to the 12V output that the wall wart provides?
two reasons: first, the wallwart‘s peaks are around 15, not 12V. second, it’s good practice to use caps that can handle at least double the voltage since they will last longer that way.
These are fantastic videos - I've been learning "modular" in Reason for years and I've gotten serious this year about getting an analog setup going. I have components, a couple breadboards and an Arduino from taking electrical engineering in college, even though I didn't go very far in it. I recently got the idea of adding a breadboard to my prospective modular rack - initially I just wanted to use it for splitters/mergers and simple logic operations, rather than buying multiple $100 logic modules - but this channel is on another level. My goal when I started learning electrical was to make a synth, but other tutorials didn't really get through to me. I made a sine bass with Arduino, but doing it with ICs on a breadboard is what I was aiming for.
I've seen other tutorials, but these go deep, they're clear and thorough and the devices are valuable and functional for music production, as opposed to a tutorial on a single isolated multipurpose component. I don't think I'm ready to mess with a diy power supply yet, but I'm definitely going to do the VCO VCF and Sequencer/Arp and have ordered the extra parts.
So dope thanks for your time and effort!
Thank you for all you Learning me i will try to support you 😊
Nice way to explain the behavior of a dual rail power supply. Thanks!
Thank you Moritz , you make great videos ... awesome
How many modules would this PSU run? would it work as a PSU for a whole rack of modules?
depends on how much power your modules need. for me, one of these will power 6-7 modules.
Thank you for explaining it in so much detail, I learned a lot from this video ( a lot of other information I gathered suddenly fell into place :))
Can i use an old pc power suply that already has - 12v? Or i need to build an dedicated one?
in general, yes, though i would advise that you use a multimeter to make sure the voltages are right.
Links to ac wall wart does not work anymore
0:56
Jameco is just a piece of plastic with a transformer and its thermal fuse
watched the whole thing but all i could think was, why aren't we using a DC supply and generating AC? that's the one thing i miss from these videos, briefly surveying alternatives so the viewer has an idea of where the technique sits overall ("this is the more affordable, this is the more efficient, this option avails this," et c.) until this makes sense to me, it's valueless.
Thank you for all the information! I build a psu similar to this but was having what I considered substantial inaccuracy :11.82 v on the positive. But I see yours is with similar accuracy. Isn't this a problem later, when control voltages are used for oscillation frequency and what not?
You can use shunt regulators on the modules to get accurate voltages. Like LM4040 you can use the 10v variant to regulate CV stuff.
This is where you start learning about the joys of Zener diodes!
Is a 500mA power supply enough for things like this? In the comments everyone is talking about 1000mA+
depends on how many modules you want to drive with it. 500mA should be enough for maybe 10 regular modules
Excellent instruction; very clear, well-ordered, and easy to follow!
Looks very fun. I will try making it
Maybe anyone can help: I built the PSU, doublechecked everythin thrice... But: The negative rail stays at -11 V and the condensators of the negative rail are getting hot quickly, so that I do not dare to use the PSU or even leave it under power more than a minute. Nay halp or idea is appreciated, thanks in advance!
I don't know if the link changed but the Jameco (US) power supply link in the description has a 3.5mm jack not a barrel jack. Alternatives: www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=2197581&productId=2197581 and www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=2227604&productId=2227604 (Only difference I can see is size of barrel jacks which is a completely different annoyance)
Is it possible to use a 8,5A voltage with 3 or 4 of those using high current resistors like those 5W ones they sell at Segor's`to "spread" the current between the rectifier-capacitor-array-modules??
This is not a good design. The transformer is designed to have equal current loads on both parts of the cycle. Unequal loading can cause overheating or failure. Also the caps have to be very large to filter the half wave rectification. Much better is to use dc in and generate the neg 12 supply from the pos supply. There are -remade products that gen pos and neg 12 from one pos input.
What should I search on Google to find it?
What if we need more than 1A?
What couldn't you use a 24V DC Adapter and Voltage divider?
Voltage dividers burn up a lot of power.
I only have aluminum electrolytic 1uF capacitors at hand, is that an issue? I also have 100 nF ceramic. What's the better choice? Willing to build this now, not to place one more order and wait...
i‘d say go for the 1 uF electrolytics. and use the 100 nF ceramics for decoupling your ICs on the actual modules. that should be decently noise-free.
@@MoritzKlein0 thanks. and i guess they're oriented like the big caps, + to the ground close to the 7912?
@@lucienrapilly6407 exactly!
@@MoritzKlein0 Did it on breadboard, everything fine, just soldered on stripboard the positive side and I now get 18 volts... Any idea about what could be wrong?
@@lucienrapilly6407 hard to diagnose from afar, but maybe you have some solder bridges? sounds like the regulator is not regulating.
electroboom will not like that single diode
nice video, very clear and didactic. U said its not a beginner's video, yet u explain the basics...
it's a beginner's video, but not a beginner's project!
I've never heard dual power supplies be explained so clearly and in so much detail. Thank you Moritz you help make these learning curves much more enjoyable!! I have a question though. Where does the ground go? (0 volts) as there's only the + and - 12v? I'm sure the answer is simple but I can't figure it out! Thanks!
Yes I came to the comments to ask the question, where is the ground rail.
@@sine0 I think you arbitrarily choose one of the wires from the wall wart to be ground/0v and treat the other like it is the source of the AC current. I think it's more intuitive if you look at the circuit diagram at 24:00 and imagine the ground connections on the bottom half of the diagram being flipped up to meet the ground connections from the top half in the middle. It looks a lot more like a rectifier when you view it that way. It reminds me of how we think of current as going from positive to negative even though it's negatively charged electrons moving in the opposite direction and you sort of accept that relatively it's the same thing.
Adafruit sells a +12v, -12v dual plug wall wart. What is the opinion of everyone of using Adafruit’s dual plug solution?
Hi Moritz, I was thinking about creating my own modules and/or little standalone mixer and effect pedal. How do I get a dual power supply out of one dc supply like pedal power (9V) or USB Power. Do you got some ideas or knowledge sources I could look up?
The link to wall wart for EU is dead !
Best channel
Crazy amount of details but not boring and not enough! Excellent RUclipsrs are difficult to come by.
Moritz, have you any experience with so-called 'laptop tingling'? For engineers like you would say it is actually capacitive coupling. Happens to all the small switching ones, transformerless, lethal, 2-prong, for mobile phones power supply. This is important as I get weird humming, buzzing, humming, and other noises besides that 'tingle'. The so-called 'audio transformer' 600 ohm : 600 ohm does not help. Maybe I am using inexpensive one. (Probably Chinese rubbish) There is no need for me to spend a lot of money because I am not doing anything professional. Only an electret microphone preamplifier.
The only way I understand how to eliminate that is to either ground it to true ground/earth or hack the mini transformer inside and place a foil as Faraday shield. Hacking a transformer is impossible for me, and to most people. So, grounding it to earth is the best way. However, I lately learnt about "balanced" circuit using instrumentation amplifier. An instrumentation amplifier an eliminate some, if not all, of those noises, and it can easily be DIY with three operational amplifiers (I have NJM5532D / NE5532AP which I think superior to the common ua741, LM741, LM358 in terms of low internal noise).
Could I put the diode on the +12 side on the output past the cap (facing out) or does it NEED to bridge the voltage regulator like shown? If so, what is the difference?
one thing to note about AC current is that there is a "ground" wire. It's called the neutral wire and is used as a 0 volt reference. instead of a positive wire, AC current uses a "hot" wire which has all the voltage. To tie it back to your water analogy, the neutral wire is basically our ground wire because it stays at atmospheric pressure (a.k.a: ground or 0 volts), while the other hot wire rises and falls in pressure 50/60 times per second around the neutral wire, which creates the sine wave you see when hooking it up to an oscilloscope.
A great teacher with analogies.
I found it nearly impossible to find an AC to AC wall wart. Are they really rare?
yeah, seems like they're dying out. i'll see if i can come up with a more accessible approach
@@MoritzKlein0 Hi, have you found something yet? I've also been looking for an AC/AC wall wart but I'm finding it very difficult. Some people suggested buying a power bank but these tend to be rather pricy for my use...
What you said about how to connect the ground clip of the oscilloscope isn't totally right: you can connect it where you want because the output of the transformer is insulated from ground, otherwise you will destroy something (probably you oscilloscope). If you want to connect the oscilloscope with more liberty, you have to make sure that only one object could be connected to ground, because it will connect everything else when connected to other devices (usually, when possible, the oscilloscope is connected to ground to ensure a better noise immunity), otherwise the ground of the oscilloscope has to be connected to the ground (otherwise there will be a shortcircuit) and you also have to make sure tu avoid ground loops and other bad things
Is there a problem if i plug in 14,5V AC? Btw, Thank you very much for those lessons! :)
Is there a reason the 7912 has an output protection diode built in but the 7812 does not?
It has to do with what falls out of the design by accident. The process of making a chip makes lots of accidental diodes as you put down one bit of semiconductor next to another to make all the transistors you need to make the circuit. In the 7912 it just happens that one of them lands is a way the marketing department could call a "feature"
It's highly recommended to also watch this video before building one of these: ruclips.net/video/UXKTkRvtZ-w/видео.html
Links don't work anymore
Does anyone know if this Would work for eurorack modules?
Such power supply only works if both poles used with same power. Otherwise the ground potential pulls to that pole that you use
If I need +-15 volts, an AC/AC 24VAC 2000mA would be suitable?
You can use class2 ac power supply cheap ones from behringer ( small mixer psu ,4 models witb different ma ) that cost about 10 euro , together with your schematic a cheap alternative that works
Hello, as said many times already: your videos are great! I am making this dual power supply but I have a curious issue: the positive rail is +12V as expected but at the negative rail I measure -6V. What am I doing wrong? Thank you.