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Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
I recently blew up (violently) my IRFP250s in the ZVS Driver with 4 fully charged 12v SLAs in series. Mind you, I was in shock (pun not intended) for a while when I was watching the impressive fire and sparks display.
I'm not surprised that it blew up, it happened at the exact moment when my arcs were around 15cm long, so there was a LOT of power draw through those poor Fets.
Anyway, I fixed the driver with new GT50N321A IGBTs from some microwave oven inverters, cleaned the charred bits up and powered it up. No arcs on 24v and 36v. I suspect the previous Fets could have damaged something in the driver? Does that normally happen when the Fets go pop? I probably need to test some of the other components (I'm guessing diodes).
If the MOSFET/IGBT doesn't have an internally built diode, how does this affect the circuit and IGBT?
I cannot find any PDFs for the 50N321 IGBTs, but I can for the 50N322. I think the IGBTs are too slow. It may not apply to the 50N321 but the 50N322s turn on time is 33uS compared to 18nS on the IRFP250.
My suspicion it that the IGBTs are too slow. I don't have any MOSFETs that are higher rated than 200v and that are fast enough and I can't use eBay right now because there are some technical problems.
Any advice?
EDIT: Sorry, slight error. I used the 50N322 IGBTs.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Man, those IGBT's are SLOW.
I would much rather go with a faster MOSFET or IGBT than that. If you want to go above that power level using the same mosfets, you should probably increase the inductor on the ZVS; Adding more turns to the core also helps, as well as increasing the zener diodes to maybe 15 volts, and the gate resistors from 470 to 1k, or around there.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Józef C wrote ...
I suspect the previous Fets could have damaged something in the driver? Does that normally happen when the Fets go pop? I probably need to test some of the other components (I'm guessing diodes).
Yes, it is common for the gate input to become a short to the source, which would cause the driver to be destroyed unless it is short-circuit protected (which is very uncommon since it's hard to have a low-impedence driver appropriate for gate driving that can also accept a short circuit)
Józef C wrote ...
If the MOSFET/IGBT doesn't have an internally built diode, how does this affect the circuit and IGBT?
This would be very bad because when the transistor turns off, the back-EMF of the inductor must be dissipated, and without the diode it would produce a huge voltage that would most likely destroy the transistor. All MOSFET's have a body diode, it is intrinsic to their design and it's not possible to make a mosfet without a body diode (although it's not a bad idea to add a super-fast diode if the fet's body diode isn't rated very well). IGBT's I believe could technically be made without one, but 95% of IGBT's, especially those manufactured today, have a diode in them.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
Inducktion wrote ...
Man, those IGBT's are SLOW.
I would much rather go with a faster MOSFET or IGBT than that. If you want to go above that power level using the same mosfets, you should probably increase the inductor on the ZVS; Adding more turns to the core also helps, as well as increasing the zener diodes to maybe 15 volts, and the gate resistors from 470 to 1k, or around there.
Yes, I do use 1k resistors for the gate drive and 18v zener diodes.
OK, I'll have to check and test some of the other components unfortunately.
I plan to buy some 47N60 and HGTG30N60B3D IGBTs on eBay when I can. They are both ultra-fast and can withstand very high powers. (FANTASTIC!)
How can you test for a diode in the IGBT? Also, if the switching time is far too slow, is the effect that the circuit doesn't resonate or oscillate fast enough?
If I said that the 47N60 MOSFET can withstand a maximum power of 28.2kW at 600v 47a, would that statement be invalid or not?
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Józef C wrote ...
Yes, I do use 1k resistors for the gate drive and 18v zener diodes.
1k resistor going from the gate driver to the gate? That is way too high, your switch times will leave the IGBT in the linear region for a huge portion of the cycle and the transistors will overheat. This may be what caused your last driver to fail. Try something on the order of 10 ohms, or even less.
Józef C wrote ...
How can you test for a diode in the IGBT? Also, if the switching time is far too slow, is the effect that the circuit doesn't resonate or oscillate fast enough?
Short the gate to emitter (turning the transistor off), then connect a current limited power supply set to <1A and set to 5V across the transistor in both directions. If the power supply on C-E conducts both directions, the transistor is dead. If it conducts only with positive-E, negative-C then it has a reverse diode that is working. If it does not conduct in either direction, it lacks a reverse recovery diode.
Józef C wrote ...
If I said that the 47N60 MOSFET can withstand a maximum power of 28.2kW at 600v 47a, would that statement be invalid or not?
Typically what you say is how much the transistor can dissipate, which is definitely not 28.2kW. It can pass 47A and can stand off 600V, but it can't do both at the same time (which would be your 28kW figure, but would never be a desirable state anyways). A TO-247 IGBT is typically rated to dissipate a few hundred watts with ideal heatsinking.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
dude_500 wrote ...
Józef C wrote ...
Yes, I do use 1k resistors for the gate drive and 18v zener diodes.
1k resistor going from the gate driver to the gate? That is way too high, your switch times will leave the IGBT in the linear region for a huge portion of the cycle and the transistors will overheat. This may be what caused your last driver to fail. Try something on the order of 10 ohms, or even less.
I've attached my schematic. What I was trying to say was that instead of the 470ohm resistor I used 1k ohm because I was running it on 48v. The 1k was to keep the voltage down the supplied the gate.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Józef C wrote ...
I've attached my schematic. What I was trying to say was that instead of the 470ohm resistor I used 1k ohm because I was running it on 48v. The 1k was to keep the voltage down the supplied the gate.
Oh, disregard my comment about the gate resistor then, I was imagining an oscillator powering a half bridge through gate drivers. I don't personally care for this self resonant topology and avoid it myself, but it does seem to work great for some people.
Registered Member #3395
Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193
I just tested the driver with some new IRFP250s and it didn't work so this is a definite sign that one of the diodes have blown. Which diodes are they most likely to be? The ultrafast or the zeners?
If the switching times on a MOSFET or an IGBT are too slow, how does the affect the circuit?
Also, I just had this on my thoughts. This probably isn't the right place to ask it, but would HGTG30N60B3D IGBTs be good for a half-bridge SSTC? Kizmo used IRFP460s in his half-bridge but they kept going pop, so I thought that a 600v 60a IGBT would be better than a 400v 20a MOSFET.
Registered Member #4078
Joined: Tue Aug 30 2011, 12:53PM
Location: Sydney, Australia
Posts: 19
I have just built a ZVS driver, and got the same problem as you - IRFP250's cooked, and after replacing them, nothing would work - I could only barely get a tiny spark after I replaced them.
I fixed it with the following:
1. Replace the MOSFETs (of course) 2. Replaced the fast rectifiers. Instead of 200v ones, I found some 600v ones (there is a lot of back emf that these need to withstand, I killed the 200v ones I think). 3. Replaced the cap across the coil - I killed mine somehow. 4. Wound a bigger inductor (20 turns around a toroid).
Now the thing is *much* better, and the oscillation is much more stable (thanks to the bigger inductor).
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Józef C wrote ...
I just tested the driver with some new IRFP250s and it didn't work so this is a definite sign that one of the diodes have blown. Which diodes are they most likely to be? The ultrafast or the zeners?
If the switching times on a MOSFET or an IGBT are too slow, how does the affect the circuit?
Also, I just had this on my thoughts. This probably isn't the right place to ask it, but would HGTG30N60B3D IGBTs be good for a half-bridge SSTC? Kizmo used IRFP460s in his half-bridge but they kept going pop, so I thought that a 600v 60a IGBT would be better than a 400v 20a MOSFET.
Well, take out what you think might be dead, and test them with a multimeter.
And, a slower MOSFET or IGBT will just result in unnecessary heat, sometimes killing it in the process. Double check to make sure everything is also connected up right, too! I've made some mistakes too, and scratched my head many an hour trying to figure out what's wrong...only to figure out I connected a diode up backwards or something along those lines.
When in doubt, double check, and test with a multimeter.
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ZVS Driver not working when fixed with 50N321 IGBTs
