High voltage h-bridge continually explodes. - Page 1
Forum section: electronics / projects

author: gecko5621
author_rank: Contributor
timestamp: August 05, 2024, 08:37:01 pm
content: Hello EEV Blog,Long time lurker, first time poster.I am working on developing a high voltage H-bridge for controlling a large electromagnetic chuck on a surface grinder. The electromagnet has a resistance of 53 ohms and an inductance of 1.5 henry. It is designed to operate at 230 VDC. I want to be able to magnetize the coil in both forward and reverse, as well as at variable power using PWM in order to adjust the power output of the electromagnet and demagnetize parts. I am in a bit of a rush to get this working (leaving town soon and building it for a friend), so instead of designing my own H-Bridge from scratch I looked into other designs.I saw this PCB design (https://www.pcbway.com/blog/technology/Powerful_H_Bridge_DC_Motor_Driver.html) from PCBWAY that seemed alright, but it was rated for a maximum of 50V. I thought I could "upgrade" it to work at voltages up to 600v by swapping the MOSFETs and passive components to operate at the higher voltage. The IR2104 was already rated for 600v, I changed the capacitors to generic 600v versions of the same values and I began using the STP33N60DM2 600V power MOSFET instead of the IRF3205. I also switched to using 600v general purpose diodes (STTTH2R06RL) for the diodes because I had them on from another project, they are relatively fast and I was being cheap. I do not see the additional switching speed and lower forward voltage of the Schottky diodes necessary unless I wanted really high quality PWM, which is not super important in this case. I figured that TVS suppression would also be good (although the diodes should be fine themselves) so I added a cheap 400V RC snubber I had from another project (https://a.co/d/fCrqfUR) in parallel with the magnet.I ordered the parts for it, it worked fine at low voltage (12V) and at high voltage in a single direction with or without PWM. Unfortunately, when I changed the direction of the h-bridge (waiting 500ms with the h-bridge off before reversing direction) I heard a loud bang and everything stopped working. The high voltage traces connecting power to the MOSFETs on the reverse side have blown apart. I have designed h-bridges like these before (for lower voltages) myself and I thought this would work. My only thought is that a very large transient spike from the inductor changing direction created an arc across the back of the board causing the traces to evaporate away.I am using a large linear power supply to create the 230VDC.I am wondering if anyone has any advice or insight into why this might have happened before I waste more time and money trying to fix it.Thanks for any and all thoughts! I am sure I have overlooked something simple.Here are the parts I am using:PCB -https://www.pcbway.com/blog/technology/Powerful_H_Bridge_DC_Motor_Driver.htmlIR2104 -https://www.infineon.com/dgdl/Infineon-IR2104-DS-v01_00-EN.pdfSTP33N60DM2 (replaces IRF3205) -https://www.mouser.com/datasheet/2/389/stb33n60dm2-1850172.pdfSTTH2R06RL (replaces 1N5819 and 1N4148) -https://www.mouser.com/datasheet/2/389/stth2r06-1851733.pdfAll my capacitors are of the same values, just rated for 600V, except C5 which is absent.

author: Andy Chee
author_rank: Super Contributor
timestamp: August 05, 2024, 09:30:15 pm
content: Please post some waveforms.At minimum, post the gate switching waveforms, but Vds for the upper and lower switches would be good.

author: gecko5621
author_rank: Contributor
timestamp: August 05, 2024, 10:00:52 pm
content: I would post them, unfortunately I destroyed the piece of hardware I was testing with and I cannot reproduce it easily (damaged the transistors and I would need to order more). I did not connect the scope when testing because I feared a large voltage spike would damage the scope and/or probes. I did check the waveforms being provided to the IR2104 as well as the output waveforms when I was testing with a low voltage supply. All of those behaviors were as expected and I did not see any shorting, or other things that would cause this.

author: langwadt
author_rank: Super Contributor
timestamp: August 05, 2024, 10:13:15 pm
content: 1/2*1.5*(230/53)^2 = ~14J that has to go somewhere

author: johansen
author_rank: Super Contributor
timestamp: August 05, 2024, 10:27:45 pm
content: Probably just inexperience on basic high voltage design as well as possible cross conduction.First off you dont actually have 1.5H worth of energy stored at 4 amps. At most a hundredth of that, so your snubber does not need to be particularly large.Your capacitors may not be large enough so i suspect you did some avalanche damage and then when reversed polarity they blew up.4 amps at 230v isnt that hard to deal with so you may consider just using a standard 120vac 3 amp variac and rectify it to drive the magnet.For demag Use a dpdt switch to drive the magnet coil directly from thr 120vac..but in series with the ptc resistor that can be found for 5$ for any standard fridge compressor.A possibility is you did some damage to the ir2104 when the switched middle node dropped below ground and then it malfunctioned. This wont be something you can measure until you duplicate your exact prior circuit and then measure the voltage with a 100mhz oscope.

author: gecko5621
author_rank: Contributor
timestamp: August 05, 2024, 11:23:56 pm
content: You are correct, I am inexperienced in high voltage design. As a matter of fact, this is the first high voltage system I am building. I fully expect avalanche damage to have occurred. Do you think it was damaged when I turned the power on the first time, then it critically failed during the switching?Is what everyone getting at that it is a foolish idea for me to attempt to use an h-bridge to control an electromagnet? I have to believe it is possible to use an h-bridge to control a large magnet. I was going to use a simple variac to control the magnet, however, my friend needs computer control. I have already implemented all of the software side items (truth be told software is more my thing). I chose h-bridge control because it seemed like the easiest solution.Is there another option I should consider? Servo drive a variac lol?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2024, 12:04:40 am
content: Quote from: gecko5621 on August 05, 2024, 11:23:56 pmYou could look at a relay to reverse direction and a simpler switching element.What is the On/Off/reverse times this needs to have ? 53 Ohms at 230 VDC is a lot of watts.If the duty cycle is there to give close / holding variations, another approach is either a dual supply design, or a power resistor dropper + cap.The high voltage is provided only for close+bounce times, then it drops to the lower holding voltage/current.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 12:15:09 am
content: The times for turning it on and off/ reversing it are not important. Up to around a half second would probably be okay. I didn't want to use relays because they are loud and during a "demagnetize cycle" they would have to turn on and off quite a few times to generate AC.What do you mean a dual supply?The electromagnet needs to hold at a constant(ish) force at all times, not energize quickly then drop back to a lower power.

author: boB
author_rank: Frequent Contributor
timestamp: August 06, 2024, 12:28:34 am
content: So, what HV FETs did you choose and what is the switching frequency ?It may very well be that using standard HV silicon FET won't work here because of their slow recovery intrinsic diodes.You might want to look into using SiC or something better for HV.And make sure the gate drive is correct for the parts you use.Proper gate drive is EVERYTHING here.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 12:51:28 am
content: I chose the ST Semiconductor STP33N60DM2. The data sheet doesn't list a switching frequency (probably because the rising and falling edges differ so greatly). I have attached those specs. I also gave a 500ms delay between toggling it, and I was running at full power so I don't think switching speed is an issue. The gate drive should be alright. I can look into SiC or similar. I am still not sure they didn't just arc the HV to the gate on the rear of the board.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 01:07:50 am
content: I forgot to mention, but I also had external diodes to support the gate diodes.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2024, 01:15:24 am
content: Quote from: gecko5621 on August 06, 2024, 12:15:09 amHow much power does this need, for what run times ?If you time the reverse pulse, you likely only need one pulse, not many.You can also add a capacitor ( + diode + resistor ) to create a LCR circuit that generates a decaying and reverse solenoid current flow, with a single switching element.The trade off there, is the voltage rating has to increase - eg a quick LTSpice check finds -1.12A reverse, with a 50% time of 29ms, with 100uF but the switch device sees 630V, as the LCR rings.

author: boB
author_rank: Frequent Contributor
timestamp: August 06, 2024, 01:17:19 am
content: Quote from: gecko5621 on August 06, 2024, 12:51:28 am500ms ? So this is only toggling at a 2Hz rate ? That should be slow enough for a silicon power FET. Unless you meant "dead time" in which you might mean 500 microseconds ?At least the die inside that ST part isn't all that small.The gate drive might be OK. I usually limit the turn off to something controllable by adding a resistor in series with the gate turn-off diode.And 27 Ohms turn on R MIGHT be OK depending on how fast you are going to switch. Both values will have some value of R where things are best efficiency wise so your FET generates less heat.But spending time on it is the way to get it going. You might blow it up several times but that's how you get there.Interested to hear how this project goes !boBP.S. Does it explode as soon as you turn it on or does it work for a little while first ?

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 01:31:27 am
content: Yes, when I first tried testing it, I set it to go in the "forward" direction for one second, turn off (disable the drivers) for half a second then go in the "reverse" direction for another second.It is discouraging that I am having trouble building something as simple as an h-bridge driver. I have done this before and such a circuit should not be so complex.I may spend tomorrow designing a proper circuit design for high voltage (instead of scavenging the other guy's board) and see how this goes. Problem is, like I said I am leaving in 2 weeks, which, generously only gives me one more good shot to get this right before testing becomes more logistically complicated.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 01:36:02 am
content: It actually ran for a considerable amount of time in the "forward" direction. Only when I tried to "reverse" it did it blow up.In order to get good demagnetization I think I will need more than a single pulse. At least that is how commercial controllers do it. It need to be able to run at full power (it draws 4 ish amps at full tilt) for days at a time.Sorry for multiple posts, misclicked on mobile.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2024, 02:11:13 am
content: Quote from: gecko5621 on August 06, 2024, 01:36:02 amMaybe there was a wiring fault in the reverse direction ?Spice says current decays to 1% in ~125ms and 0.1% in ~164ms, with a direct clamp diode.

author: amyk
author_rank: Super Contributor
timestamp: August 06, 2024, 02:45:36 am
content: Does it really draw ~4A continuously in operation? That's around 1kW of heat output.I agree with the others here that relays are likely to be the best choice for this application.

author: Circlotron
author_rank: Super Contributor
timestamp: August 06, 2024, 03:17:13 am
content: Quote from: PCB.Wiz on August 06, 2024, 12:04:40 amThis.It would make things sooo much simpler.Just make sure there is no current flowing when the relay changes state and it should last practically forever.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 03:21:12 am
content: Perhaps there was a wiring error, I don't think so, but I will look at it again.I will probably redesign it to use relays. Hopefully I can come up with something clever. I am still interested in how this could be accomplished with solid state electronics. Could I use a big power BJT to control the output, that would probably generate a lot of heat? Perhaps I can use a large power MOSFET to control PWM, a relay for toggling between "on" and demag and a PTC resistor with AC for demag.Yes, it is a continuous 4A draw. This is a large industrial chuck, 3x4.5 feet approximately. It needs to run essentially indefinitely because it will be in production at a grinding shop, setups commonly run overnight and grinders run all day everyday.

author: boB
author_rank: Frequent Contributor
timestamp: August 06, 2024, 04:03:38 am
content: Look up "catch diode"Maybe the FET is being avalanched too hard or something like that.Look for voltage spikes.you have a good size input cap, right ?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2024, 05:05:39 am
content: Quote from: gecko5621 on August 06, 2024, 03:21:12 amHehe, that thing is not just large, it is massive ! I guess 1kw is ok in that volume of metal and copper !Quote from: gecko5621 on August 06, 2024, 03:21:12 amIf it runs continually fully powered, what is the PWM needed for ?It is harder these days to locate a high voltage BJT, than it is to find a MOSFET.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 01:51:22 pm
content: Different grinding setups require different amounts of relative power. Honestly I am not 100% sure why, but the grinding people enjoy it. What is important though is that once a power is set it doesn't vary too much, variations in power (like dropping the chuck power 80% or something can cause small shifts in the material. That is not ideal when you are trying to grind to the thousandth or ten thousandth of an inch.I looked at flyback diodes (I think this is what you mean by catch diodes), but I can't put one directly on the chuck because it needs to take AC, and I have diodes already between all of the sources and drains of the MOSFETs which should function as flybacks to prevent reverse current, in addition to the ones intrinsic to the MOSFETs.If I used relays and fed direct AC to the chuck for demagnetization I could add a very large flyback diode before the relay (perhaps one of mine from a microwave oven?)I have a large input capacitor. 3300 uF 350VDC. When I run the chuck at full tilt without the h bridge it has no problem powering it, and it is relatively consistent with it's voltage according to the scope.

author: MrAl
author_rank: Super Contributor
timestamp: August 06, 2024, 03:26:19 pm
content: Quote from: gecko5621 on August 05, 2024, 08:37:01 pmHello there,Welcome to the world of higher voltage H bridges (like with a 200vdc and up buss voltage).The problems that come up are quite numerous. Spikes across transistors, higher than normal currents, dead time, etc. One thing we don't talk about too much though is EMI where the thing being driven interferes with the control circuit.Because this is a pulse type circuit, there would be high harmonic radio frequency emissions and those could cause some part of the control circuit to hiccup, just long enough to turn two transistors on one side of the bridge on at the same time or cause a multiple pulse through the transistors that are supposed to turn on, which causes multiple rise and fall events when there should be just one.There's also the source terminal wiring, which can cause oscillations, which causes the MOSFETs to turn on and off many times before at last it turns on fully.Those are some of the problems that come up. The thing is, there are so many possibilities that it's hard to figure out what is not working right when we are really blind to almost every signal in the system. This means the only way to find out is to perform tests.As you know, replacing the transistors and whatever else (including possibly the drive transistors if there are any, or possibly the driver IC chips) and firing it up again will just show you how to blow out more transistors. That means we have to have a decent strategy to attack this problem.The tried and proven way is to run the entire device up 'slowly'. That means providing proper power to the control circuit but not to the DC buss. The DC buss gets powered by a separate power supply. That allows us to get the device working at a much lower voltage and check for problems at that lower voltage before we turn up to the full power. You can check for problems with a scope.You can also install fuses for lower power testing. Sometimes you can place a fuse AFTER the input filter caps. That helps to protect the transistors if something goes wrong. They will not be able to access the full energy stored in the caps.When I worked in the industry years ago, the input filtering for the high power converters (could be 5kW for example) would be made with multiple high voltage caps and copper buss bars. If the transistors try to discharge those caps when a problem comes up, they blow out.Back then before MOSFETs were popular, high power bipolars were used. These things were big and stud mounted with 1/2 inch copper studs. If something went wrong, it would take out all four (or six) transistors, and each one would cost $100 USD or better. That's at least $400 and all the transistors had to be replaced and that included all the driver transistors. It is customary to change the driver transistors when the bridge blows because they could be damaged internally and still appear to work (for a while that is).So anyway, that's how a high power converter with an H bridge or a three phase bridge can be tested without destroying the transistors. If you decide to try again, at least you will have a reasonable way to approach the problem.

author: johansen
author_rank: Super Contributor
timestamp: August 06, 2024, 05:16:33 pm
content: your IR2104 needs a continuous charge pump to keep the highside mosfet ON at 100% duty cycle.so lets figure 95% maximum duty cycle.rebuild the circuit with sufficient capacitors located very near the H bridge to absorb the energy and use a good quality oscope to measure the peak voltages produced when you turn it off suddenly instead of say, reducing the pwm percentage slowly.I think what happened here is the highside mosfet shorted out internally when the gate voltage dropped through the linear region.then when you reversed the polarity you blew up the highside and low side switch.you may still have 1 good high side and low side switch.the ir2104 only appears to have a low side undervoltage lockout. when the gate voltage drops on the highside boost strap supply, it will not turn off suddenly at say, 7 volts. it will drop slowly to 0 volts.

author: gecko5621
author_rank: Contributor
timestamp: August 06, 2024, 08:46:21 pm
content: It is interesting that you say I may have 2 good switches, because it appears that I may have 2 good switches, one on the high side and one on the low side (at least they appear to not be shorted with the continuity tester). I do have a pretty large capacitor on the h-bridge (3300 uF which is giving me linear power and it is very near to it. I don't see why the gate voltage dropping through the linear region would cause an internal short. I also waited 500ms between turning it off in the forward direction, then back on in the reverse direction. I feel as though I am not understanding something about this though.I did try testing at 12v and it seemed to work fine. If/when I get around to trying this more I can more slowly increase the voltage with my variac or something for testing.

author: langwadt
author_rank: Super Contributor
timestamp: August 06, 2024, 09:13:07 pm
content: Quote from: johansen on August 06, 2024, 05:16:33 pmand while there's flyback through the body diodes one of the highside boot strap supplies are not charging

author: johansen
author_rank: Super Contributor
timestamp: August 06, 2024, 09:33:25 pm
content: Quote from: gecko5621 on August 06, 2024, 08:46:21 pmyes i think that's what happened. mosfets have a linear region in which as the gate voltage drops, its resistance rises, and it heats up. once it rises above a certain temperature damage occurs and it stays a bad resistor with local hot spots. if it keeps up, it will turn into a short and your circuit will give the appearance of being able to stay on forever.however the rate at which the gate voltage drops will also be proportional to the leakage current through the boot strap diode which is proportional to the supply voltage. At 12volts, (and very low current through the magnet, thus it matters a whole lot less if the gate voltage on the mosfet drops) you may be able to hold it on for 10 minutes before the gate voltage drops to say, 4 volts or less and the high side mosfet starts turning into a big resistor.but at 200 volts it could happen in 10 seconds (and a lot of that has to do with how clean the board is and the exact values of the diode, capacitor, etc)

author: johansen
author_rank: Super Contributor
timestamp: August 06, 2024, 09:44:29 pm
content: Quote from: langwadt on August 06, 2024, 09:13:07 pmif current is flowing through the highside body diode then that means the voltage was previously reversed and already charged up the bootstrap.

author: langwadt
author_rank: Super Contributor
timestamp: August 06, 2024, 10:22:21 pm
content: Quote from: johansen on August 06, 2024, 09:44:29 pmsure, but for how long with the leakage current through the boostrap and current consumption of the highside driver ?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2024, 10:23:43 pm
content: Quote from: gecko5621 on August 06, 2024, 01:51:22 pmSo you need to control 80% to 100% ?As mentioned above, if you want to get to 100%, you need a special high side driver with a charge pump, that is designed for 100% duty. Simpler ones are not.What PWM frequency did you choose ?The simplicity of a single decent MOSFET and a good flyback diode appeals, with relays for the low-usage cases. Simpler than 4 FETS + 100% Drivers, especially for one off.You can get 10-20A fast recovery diodes, and for 80~100% duty, their power loss is not too bad. Good ones drop just over 1V.A package like TO220F is easy to mount.Addit: Since this is solenoid drive, you could look at LED Switching controllers, designed to drive a NCH MOSFET, and with a low current sense threshold.Parts like IL9910 et al have 250mV sense and 450V vin max, with > 6.7V gate drive.Current drive gives you temperature compensation of force, as solenoid heating lowers the current when voltage driven.As a bonus, you get current sense and protection in your MOSFET for free.

author: jonpaul
author_rank: Super Contributor
timestamp: August 07, 2024, 08:17:01 pm
content: Gecko...After decades of HV and power electronics, a few moments please...1/ 200..400V is not considered "high voltage" by most.2/ industrial motor reversers use a DPDT relay or contactor and NOT an H bridge. Usually rated for AC DC, contact amps, contace voltage.Many ciol rating 5/12/24/48VDC and 24/120/240 VAC.3/ H Bridges require floating drivers, clamping of stored energy in load, gate and drain protection (EG TAZ Zeners)Costly and complicated for wat you need.4/ Equipment and instruments used to desgin and debug:Good scope (not Chinese junk)mains isolation trsf10x and 100x probescurrent probesBon CHance!Jon

author: MrAl
author_rank: Super Contributor
timestamp: August 08, 2024, 08:44:39 am
content: Quote from: gecko5621 on August 06, 2024, 08:46:21 pmYou should read all of the replies since your last read not just the very last one.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 08, 2024, 08:15:13 pm
content: Further to my #29, google finds this relatively new part1ED44173N01B Single-channel low-side MOSFET gate driver IC with fast OCPThis is simple and cute : it has SOT26 packageOver-current detection (OCP) with negative voltage input-0.246 V over-current threshold with accurate ±5% toleranceUnder voltage lockout for MOSFETsCMOS Schmitt-triggered inputs3.3 V, 5 V and 15 V input logic compatible25 V VCC voltage supply support (max)-10 VDC negative Input capability of OCP pinThe negative sense means you connect Gate driver GND to the Source, which removes gate drive spikes from the sense resistor, and lowers gate drive loop inductance.It's much faster than you need, but a series gate resistor slows things down.The simple current sense means it can drive the FET 100% until the threshold is hit.If you connect IN and FLT monostable, I think it will then oscillate using a fixed off time to reduce the current. Should be fine for 80%-100% range.A local inductor and RFI cap, could isolate the cable and machinery from the worse edge speeds, and keep switching losses lower.

author: amyk
author_rank: Super Contributor
timestamp: August 09, 2024, 02:22:42 am
content: Quote from: gecko5621 on August 06, 2024, 03:21:12 amThere are a few old long-expired patents that give examples of how to do it with solid state - e.g.https://patentimages.storage.googleapis.com/c2/dc/35/bbbf12c75a2f1b/US4633361.pdfand the ones related to it may be worth inspecting.

author: MarkT
author_rank: Frequent Contributor
timestamp: August 09, 2024, 05:56:31 pm
content: I'd add consider using IGBTs for this, they are more robust at high voltage as the gates is less directly capacitively coupled to the drain (collector) dV/dt transients. Ultra fast switching at high voltages is way harder than you might think, all sorts of issues - usually the PWM frequency is kept lower and slower switching used to tame the dV/dt and dI/dt, at the expense of switching losses (mitigated by slower PWM).High voltage high power H-bridges are mainly about protection circuitry, not a simple scale up from a low voltage low power design...

author: Andy Chee
author_rank: Super Contributor
timestamp: August 09, 2024, 07:37:45 pm
content: Quote from: MarkT on August 09, 2024, 05:56:31 pmAnd just a reminder, IGBTs don't have an intrinsic body diode. So make sure you use an IGBT with a reverse diode built in, or supply your own external reverse diode.