All You Need To KNOW About CROWBAR Circuits To FIX Stuff! How crowbar circuit works tutorial
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- Опубликовано: 17 фев 2023
- The Crowbar Circuit. What Is It? What Does It Do? This video came about due to some comments on an industrial repair video I made recently. A subscriber was asking if a diode on the PCB was a crowbar circuit. Not everyone seemed to know about this type of circuit, how to recognise it and what it does, so I decided to make a shortish video.
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Thank you
Richard
I'm doing electronics on and off for nearly 40 years now, but never came across the term "crowbar circuit". Never too old to learn something new, thank you for this and all other vids you do, keep it up!
Ne neither. But I'm glad I know about it now. 👍🇮🇪🙏🏻
You were obviously never a burglar and Richard well say no more ! Why else would you need a crowbar ?
I too have been an electronic hobbyist for over 50 years and although I have heard the term "crowbar circuit", it more commonly is known as "over voltage protection". I'm sure you've heard that term many times. Watching these videos is almost as much fun as doing the experiments your self. I think this fellow used the term "crowbar" because it would gather more attention in the title. He did a very good job explaining this.
Crowbar refers to the shape of the graph that looks like a crowbar when plotting the output voltage to input voltage on the protection circuit..
I worked on legacy industrial control systems for decades that used very large linear power supplies. All of the power supplies had crowbar circuits to protect from overvoltage as well as overcurrent. The difference was that with the design I worked with the SCR would hold the power supply off through the circuitry until the power that fed the supply was cycled instead of blowing the fuse. Those systems were built during the 1970s.
I was introduced to crowbar circuits while repairing Astron linear power supplies. This circuit has saved many expensive pieces of equipment and is well worth taking time to understand how it works. Thanks!
I'm really surprised how many people have never heard of an overvoltage crowbar. I remember seeing a great example circuit in "The Art of Electronics" way back in late 80's when I was a teenager. I've also owned linear regulated power supplies that incorporated the circuit in case of a pass transistor failure.
That's the BEST crowbar class I've been privileged to watch! Thank you! Great class, Richard!
Well that had just about everything you'd want...good explanations, schematics, practical examples and demonstrating to destruction! Many thanks Richard, extremely helpful.
Excellent video! I really like your pedagogical approach. You start with a simple design, then formulate a hypothesis ("this component should blow when we add the extra voltage ..."), then test that hypothesis, demonstrating the expected effect, and then add a layer of complexity, i.e., the Zener. All this is clearly demonstrated on the perf board. This layered approach is great for people to absorb your knowledge step-by-step, and teaches not just electronics repair, but also design. Well done.
Yes. As someone just learning, this is far, far easier to understand this way.
FWIW: An alternative to using a SCR (Thyristor) is to use a TVS diode, which is zener diode that can handle high current. TVS diodes come in Unipolar or bipolar (so they can work with AC power).
For DC circuits I recommend a PTC fuse & a unipolar TVS diode. A PTC fuse is a resetable fuse that transitions from a low resistive component to a high resistance component with the trip current is exceeded. with a PTC fuse and a unipolar TVS connected to the PTC & ground, it will operate both as a overvoltage protection, Surge Protection, and a reverse Polarity protection. This is better than a Glass fuse since the PTC fuse does not need to be replaced everything the trip current exceeds its rating. Once the Power is removed for about 10 to 30 seconds, the PTC will reset back down to a low resistive state.
I’ve come across them a couple of times - well explained 😀👍
... we will now have a short period of mourning for the components who sacrificed themselves in the making of this video 😢. .. in a good cause.
Brilliant explanation , takes me back to my young days , you don't get guys like you any more who can simplify electronics as you do .
Never heard of a crowbar circuit, but this was an excellent explanation of what it is and how it works.
Thanks for the refresher of this simple & yet elegantly designed protection circuit. I'm a technician who has spent my career in the electronics QA department, two steps removed from the circuit troubleshooting / design of PCBAs. It's interesting to view these informative presentations.
I am just a dabbler in electronics (home brew amateur radio) but this video, indeed all your videos are extremely helpful. Many thanks. All the best mate.
Brilliant explanation! The gentleman proved that he knows what is he talking about.
Thanks, good topic. As an old retired guy that worked as a tech in electronics since before white LED's existed, seldom have I found people that knew of this circuit. Most small commercial switching power supplies that I have evaluated in the last 40 years have had crowbar circuits on the outputs as standard. One issue I wanted to point out is that on failing power supplies, this circuit, especially the zener diode, is often the cause of the failure.
"since before white LED's existed," wooowzers :)
@@garygranato9164 Oh white LEDs are relative new-comers. I well remember before we had blue ones! 😁
@@LearnElectronicsRepair your correct ! i thought they were invented in the sixties but google says white led invented in 1996. so yes the white one are quite new.
@@LearnElectronicsRepair I remember when the blues came out and we were so exited about them that we used them everywhere. I think the guys who invented them got à Nobel price. But I'm not sure about this. Time fly...
@Martin Major lol I wrote my secondary thesis on Blue LEDs N what it meant for Hard-drives to & what would soon become laser disc's 😅. good oledays.
This was a great lesson. I learn a lot by watching your videos because you explain in very simple terms, the how's, why's and where's of a circuit. I wish I had known this years ago but I have a learning disability for comprehension. the way you explain things make it very easy to understand, thank you!
I love the simplicity of these little circuits. Beautifully effective and simple
After two years in technical school, almost exclusively theory not much bench work, I got a job with a railway company. New guy gets to fix handsets, boring. But the power supply on the mic test bench belched out smoke and gave up , they handed me a manual and said have a look. I was soooo scared , but figured out the a zener had failed and was keeping the crowbar on all the time. After fixing it I imagine the smile on my face was ear to ear. First thing I ever repaired and first time i had ever heard of crowbar cct.
I certainly learn a lot from you. I think being shown rather than just reading about stuff is much better. I enjoy all your videos. Thank you for being there for us
23:37 "The Dot of Death". Born in the "Flash of Failure".
Great video and thanks for posting it.
I've been in electronics long enough that I learned about vacuum tubes. I don't recall learning about crowbar circuits. You explained it beautifully and it's knowledge I know I'll use at work in my troubleshooting. Thanks mate. I'm a subscriber now.
The crowbar circuit was an excellent choice to discuss and demonstrate. In my roughly 45 years in electronics I've seen it used many times in different variations. One similar circuit was used to shut down the power to the load if the current drain became too great, thereby protecting the power supply itself while indicating a load fault.
One good reason to use the SCR is that it forces you to shut down the main power source. As in your example to replace the fuse, or in others to remove a shorted load.
great video I have herd of crowbar circuits but I didn't understand them until now I like the way you show how it works in a way that everyone can understand.
Great circuit to save some equipment. I never knew about this circuit until now and I have been tinkering around with electronics for almost 50 years. I have been interested in electricity ever since I was a baby. My parents said that I was fascinated with the light bulb and at age 4 I was in the paper across the whole country. The associated press picked up the story the local paper did on me and my light bulb collection. Thanks for sharing.
What a fantastic tutorial. You're a great teacher! This circuit could be called a Fuse Killer 😇
Useful topic. In a real world design, it’s very important the SCR cathode is connected directly to the supply ground and not via shared ground wiring. If it is, as here, the momentary high current can lift the ground potential and what you thought was always 0 volts isn’t any more.
This and the I2t datasheet parameter tuned to the fuse plus the capacitors to discharge in such way the overshoot doesn't propagate to far.
@@codures he means I2R, "I squared R" for those that didn't understand.
@@terryschabert7929 it's "I squared t", t like time - it's called "fusing rating".
At the point where the SCR decides to turn on, things are already snafu; what's really the problem with load-side ground being (even inhomogenously) above 0V for a few milliseconds? Is your concern that the load-side ground wiring might not actually have a sufficiently low resistance to let the fuse blow? Or are you talking about equipment with a 400V DC bus where "ground" being, say +150V for a few milliseconds while someone's touching it might still be a problem?
@@bpj1805 nope, none of the ones you mentioned. 1. Current flows according to Kirchhoff's law. 2. If "Ig" fluctuates due to "Iak" because there's a huge R (hundreds of mOhms) the turn-on of the SCR is not as linear as expected for those critical tens of micro-seconds. 3. The return path and the overall design might be so "effective", it may even worsen things (see 1.). Hope it's more clear to you.
Thanks a lot. Clear simple explanation and demonstration. You've taken me back to the mid 70's when I was at the Army SEE at Arborfield. 50 years of electrical and electronics and now my main hobby is old motorbikes !
I’m the same as you almost. I was Trained in Electronics in the Air Force. I grew up before the Air Force helping my Dad do Electrical work. Got out of the Air Force and went back to doing Electrical and Electronics and now at 62 I’m back into Motorcycles. Small World.👍😁
@@joeybobbie1 Hello Joeybobbie,
I bought a Morris minor a month ago so now I've got a 1950 bike and a 1967 car to play with. 1967..............hmm that's the year I came out of my time at the pit. 4 years before I joined up
All the best, Colin.
RUclips algorithm brought this video up. Excellent presentation on Crowbar Circuits! Thank you so much for sharing your knowledge. You have a new subscriber.
Awesome Richard. I’m very new to electronics so it’s taken me a few months of dipping back into this video to get it. Thank you so much, please more videos like this!
Excellent video. I just got my ham license and while I learned some electronics in the course I took, your description and explanation of the circuit was very clear and informative. I ended it knowing the what it does and why it does it.
I am subbed to a ton of electronics channels, many focused on teaching. I must say this channel is the best for me learning wise. It's not overly basic nor overwhelmingly complex. You also explain things in very easy to absorb terms and at a good pace. I appreciate your scenarios are practical and easily applicable to the real world. You only focus on theory when it's important to understand for the given tutorial. Anyways, I'm glad I came across this channel! Keep up the good work.
While reasonably educational it itself, it still contains quite a few errors. I think it's good practice to not have beginner errors (which are not on purpose and explained as such in the video) when teaching beginner subjects.
- no current limiting resistors for the LEDs
- missing 100nF caps on the 7805 (no, 100uF is not an acceptable replacement!)
- missing diode across the 7805, which is mandatory if you have a large output capacitor
- the oscillator circuit takes input 1 of the chip negative, when pin 4 goes low, because the capacitor is charged to about 2/3 of the supply voltage. The 10k resistor will limit the current, which prevents damage to the IC, but I think that should be explained in the video.
- a TVS is NOT a "bidirectional zener diode", it is a very different device, but from a distance can appear somewhat similar in behaviour. TVS come in unidirectional and bidirectional flavours, and are specifically designed to absorb huge amounts of power during short voltage transients. I've used one that could handle 300kW (not a typo, really, three hundred kilowatts!) for a very short time (about 100us)
- The crowbar itself is mostly ok, but you should consider the thyristor gate trigger voltage, which usually is about 1.5-2V, and add that to the zener voltage; that means the supply voltage could rise to about 7.5V before the crowbar trips. If it rises quickly, the expensive chips may or may not survive. It is happens slowly, the chips will probably be dead before the crowbar trips.
Crowbar circuits are certainly useful, and I've used this exact circuit many times, but it's hard to design such that it will always trip before the chips are damaged, and at the same time will not trigger unnecessarily. I usually have one connected across a bench power supply if it's supplying something particularly sensitive, set just above the target voltage. This isn't there in case the supply fails, it's there in case the idiot behind the desk (me) starts turning the knobs of the wrong power supply.
Also, if you replace the thyristor with a triac, it will also work for reverse polarity conditions, with the limitation that there will still be about -2V across the circuit while the fuse hasn't blown yet.
@Ton Fleuren you should have a channel!
Agree!
Complete novice here, but this makes perfect sense as you've explained it. Proper fuse application engineering. Very cool, thanks for the video explaining it!!!
Having worked on large, lab grade high voltage power supplies and other high power RF systems for the last 16 years, crowbars are pretty much a daily topic for me. Our stuff monitors current, and if it exceeds a spec, it fires a hydrogen thyratron or an Ignitron to short out the supply and protect the DUT.
Cleaned a few thyratrons over the years because of random trips caused by contamination conducting just enough to throw a crowbar into my day off. 🤣
Richard this video was very helpful. Can you do more videos like this. Learning how a circuit work and recognising different circuits certainly helps in the diagnostic procedure.
Awesome video.
I'd like to see more !
I like your repairs but that kind of specific technical point is very useful as you cannot explain during repairs.
Thanks from France for your contents.
Very wel done. He very well knows his stuff, has no problem explaining.
I've learned more electronics stuff in this video than in any book I've ever read on it
I've put TVS diodes on my circuit for in my car to protect against transient spikes, but this is a brilliant addition, I'll be adding this to my version 2, more sensitive/expensive electronics will certainly benefit from such a thing, and I imagine I could do similar for the inputs as well.
Ive been in electronics,for 45 yrs,since i was 9 yrs old.fixing radios ,and cassette players,other stuff.electricals.since then.ive worked at a lot of electronics,industrial companies,and have seen crowbar circuits.in there designs over the years.i never get bored of electronics.i like how you teach ,explain,and demonstrate,sometimes to destruction.great video of this circuit.thankyou.keep on making the videos!👍👍😀😀
Richard, your videos are all excellent. You should of been my lecturer when I studied electronics years ago. Keep up the fantastic work. Thanks for sharing your wealth of knowledge and experience
I'll second that statement! To be fair to my first teacher (he was terrific) I never had the chance to get to the 2nd and 3rd courses where these matters were covered with him, but his system was very much like yours, Richard. You guys are rare! I'm glad to have found you even after having worked in the field of electronics for nearly 40 years.
I have done electronics 45 yaers ago.but only pracyiced it for 3 years. You remind me of the tutor I had.I subscribed and hope I can be refreshed and come to know a little more.. Thank you.😀.
Thank you. Interesting. Never heard of a Crow Bar Circuit. It's fun to watch these videos since I reset up my Electronics Laboratory Bench after 20 years. I decided to get back into it. Electronics isn't about making money, it's about having fun 😊. Thinking about getting back to correspondence schooling again.
Recently repaired a motor control circuit where one of the motor reverse relays has fused contacts. Normally, the motor runs in the forward direction so when the circuit is activated, the motor is commanded to run both forward, and backwards (due to the fused contacts in the relay) at the same time. No crowbar circuit was needed to blow that fuse. Lots of fun!
Nice video. Keep it up.
Yes, brilliant. This is a refresher for me and a good thing.
GR8 video...
I 2 have never heard of a "crowbar circuit"...
Until now...
Thank you! This tutorial was at the perfect level of complexity. Thanks especially for the asides explaining or reminding of small details like "thyristor, SCR, same thing".
This type of video is very useful as a building block for electronics.
Thanks for another great video, and I very much appreciated this "hands on" format as a complement to your more purely theoretical ones.
Brgds
A very lucid explanation and demonstration - thanks for taking the time and effort to educate a newbie to electronics like myself - much appreciated.
Bravo! Explaining away the complexities of power supplies!
Good evening. The first time I saw a craw bar circuit was inside the power supply section feeding a very expensive RF subsystem inside a mid-eighty HP instrument...A period when they gave value to what was actually worth of. Regards from Italy.
Thank you Rich for teaching us so many different things. I really enjoy all of your videos! Gracias 👍
For those who have some electronics knowledge and simply want to know what a "crowbar circuit" is, it is a zeiner diode that will cause a fuse to blow if a voltage regulator fails and allows too much voltage through. Good educational material overall.
The first time i came across this circuit that used the name crowbar was in the mid 1970s in the decca 80 colour tv set .
it was connected across the HT output on the power supply.
I was told the reason it was called crowbar was because of the shape of the waveform when it opperated.
Fantastic educational material. I love how practical this information is. Thank you for taking the time.
Thank you so much for this video! You have a natural gift to teach!!
More, please.
These types of videos are incredibly educational and useful.
Didn´t know that one - cool idea.Thanks for teaching us Rich! I think, you - showing us types of circuits and explaining them - that could make for a cool series of videos and for me personally - it arms me with more understanding and knowledge about circuits I could possibly encounter when repairing stuff + those are also nice ideas one can implenent in ones own designs.
So - thanks once again Rich for the good work!
Cheers from Vienna, Austria
Very interesting. I think this would make a great mod to add to retro devices that use irreplacable chips. Seems to be rather effective, it only requires 3 parts, 4 in case there is no fuse and you have to add that, too.
Absolutely! Most available switching power supplies are equipped with crowbar circuits now. If you are building custom circuits with no crowbar designed in, it's a great idea to implement!
Excellent tutorial Your explanations and demonstrations are truly enjoyable and informative. thank you for another excellent video.
"Anything could happen in the next half hour." Ha! Great Thunderbirds reference!
Nice and clear, really interesting for a retired aircraft electrical/avionics tech( aged nearly 80 yrs) to keep abreast, purely out of interest , but now, I am gradually seeing what some of these puzzeling sub circuits i come across in my repairs may be for Thank You Learn Electronics Repair 👍👍👍👍😊😊
Thanks for the lesson. I don't know much about circuits except what most of these components are. Your explanation taught me something new. I get it. Thanks!
Im amazed by your( components) drawings. thanks for the fantastic teaching.
This circuit was common in the Astron power supplies used by the Ham radio community... Glad to hear it explained ... TY!
A very simple and straight forward explanation.
I will try to adapt your way (if I can manage 😊) in my lessons.
I remember this from the 1970's but had forgot it till now, very good, thanks for the reminder..
Great video. Please keep them coming. These type of circuit videos are great knowledge to have. Thank you
Remember that bag with "shorted" caps you used for the DIY supply ?
Those were in fact 100mA PTC fuses, which will reset when supply is disconnected and PTC cooled off.
Perfect in crowbar circuits such like this one ...
Maybe you are referring to PTCs as NTCs lower their resistance as they get hot. I don’t think I have seen PTCs in crowbar circuits though…
@@hernancoronel Yes ! Thanks for the correction !
I have corrected my comment according to your notice.
Most common example is the Littelfuse range of resettable PTC fuses .
Thanks
@@CXensation Ahh so that is what they are for. The problem with an sort of fuse is that enough current has to flow to make it 'blow' and that already killed the voltage sensitive devices you were trying to protect. With the crowbar, it is voltage triggered not current triggered which usually means it can act fast enough to save your circuit. You will find this circuit (or similar variations of it) in quite a lot of industrial applications, which is why I wanted to familiarize everyone with it
@@LearnElectronicsRepair AFAIR the ones you have in the bag are 100mA types.
You could do this demo over again - but change the subject to PTC fuses 😀
@@LearnElectronicsRepair In my work place an extractor fan broke down so they called me. This kind of extractor fan I have never seen before. There are six wires going into the fane. The circuit was outside so removed it. but When I tested it I mean the wires for continunity was surprised that only two wires has continuity but the others has no continuity to anything. So I took a new one and started it and then also disconnected that one and tried to test the six wires going into the fane but that one also only two wires has continuity and the others do not have any. Now this is strange. Could it be that there is another circuit inside the fane somewhere when the line because live somewhoere the relyas owr some electronic switch will closes in so then there will be continuity? If you can share your thoughts will appreciate it.
I think this is my first time seeing your video, and I really like your approach.
This was excellent ! Very well done. First time I've run across your channel.
Wonderful demonstration Sir!
I wish I had you as my circuits I and II professor in college. I can't tell you how many times I would ask a question about a specific part like "Why is C2 nessecery off the base of Q1?" or something along those lines and the answer came back in a fashion that not only didn't explain it at all, but was almost condescending. "Oh yeah the capacitor adds capacitance there, but you should already know that.... moving on!"
You explain things well, everything made sense the first time around. Thank you for your educational videos they are truly great. I have worked with these circuits when repairing high powered power amps for audio. I knew they were used to protect the speakers should the output transistors fail, placing the DC from the power rail directly onto the speaker coil and frying it (or actually setting them on fire if the rail voltage was high enough!). I always knew "what" they did, and what they looked like, but not "how" the circuit operated until now. Thanks!
Love the interactive explanation....very detailed. Thank you so much.
That was brilliant I to have been playing with electronics since I was a kid , I learned a lot very well explained and demonstrated thank you.
Excellent explanation. Going from the problem to the solution, it makes perfect sense 🙂
Very good practical explanation. Thank you very much.
Great little circuit as electrician I can understand . Keep up with the great work. I will in co-operate into my hobbyist circuits . I am enjoying the unstanding how electronic circuit work but haven't made any thing useful yet. This a hard concept to grasp , shorting circuits to ground as most of my working life was putting in circuits that prevented from touching earth or ground
Great Video, and as always, perfectly on topic. One thing you could add, In my experience, is a diode from the output back to the input to protect the regulator from the reverse current flow if it triggers spuriously. This also protects the regulator from reverse current flow if the power is switched off and the caps on the output of the regulator are quite robustly proportioned. Keep up the great videos
Excellent tutorial and demo. Thank you.
Absolutely a great video Dicky, the explanations are awesome, keep up the great work mate 🤙🏼🇦🇺
Quiet savage really and you don't see this used much anymore cos its proper belt and braces stuff. I couldn't remember myself much about it until the moment you said "like dropping a Crowbar across a car battery" then it came flooding back ! just blow the bloody fuse until we can get an engineer out to sort it !..fantastic tutorial....cheers.
Beautifully explained, thank you. Subscribed btw. Great content.
While you were explaining, I found my mind staying occupied trying to find out what is it function and where it is used, try to early on introduce an overwiew of the purpose and orietation of what you are and going to talk about, besides the above I find your tutoring very pleasant and easy to understand. You have helped me a lot understanding this "new language"
Great job of explaining and demonstrating. Regards from South Africa.
Amazing explanation!!! Priceless! Thanks for the gift of knowledge.
NOW, I understand what a Crowbar circuit is and does. I believe I will incorporate them in my future Microcontroller PCBs. Thank you Richard.
I've never heard that term for a circuit before and learned something new. I also really need to change my phone's alert sound... I keep thinking my phone is going off every time I watch your videos. LOL
Many thanks Richard. Heard of 'Crowbar' circuit when I was an apprentice. (Lord known how many years ago!) An excellent explanation. Well done you!
Very good explanation and demonstration. Thanks!
Really enjoyed this one. More like this will be most welcome. Many thanks.
Hi, New Subscriber. Thank you for making this Video. Very well explained and presented. I really learned a Lot watching this. I’m glad I found your channel and will be Watching all your Videos. 👍👍
Great video of the Crowbar SCR OVP circuit.
Some 10 years ago, when I was new to electronics, but not engineering in general. We have designed a multipurpose clock/temperature sensor/alarm kind of device. We printed the PCB ourselves, soldered TQFP microcontroller with 7805. Tested it and everything was fine. Later on we powered the thing again but this time we got magic smoke. When we probed, 7805 was blown and was shorting. MCU was a cheap one but desoldering and resoldering it was hell.
I put crowbar circuits into my LED power supplies to protect the expensive LED COBs. I use a PNP power transistor with a current sense resistor in series before the regulator to make a custom over current crowbar. Rather than relying on blowing the fuse, I use the crowbar current to trigger a regenerative switch to kill the power on relay. When the crowbar activates it also shunts most current to ground in the milliseconds before the relay drops.
Great explanation, very clear. Thank you!
Thanks Richard. A great demo.
This was a great tutorial. Thank you. Would love to see more.
Great circuit, Richard. Learn something else today. Thank you.
Thank you, very well explained and demonstrated..
The best explanation EVER!