| Electronics > Projects, Designs, and Technical Stuff |
| Book for Gate Drive design and IGBTs |
| (1/4) > >> |
| Glenn0010:
Hi all, So as a graduate Power Electronics engineer, after a year working on various things in R&D of a drives company I get what I've been after! I am going to be designing the gate drives for our new product line. I have already designed gate drives before for my bachelors thesis so I have a pretty good grasp of things. However I want to do the best job possible. Further more in the past we have run into some issues during short circuit testing so I'd like gather more information on how these can be sorted from the onset. Are there any good books which talk specifically about IGBTs, FETs and gate drives. Things such as the Kirk effect and so on. Thanks for you help as I've been struggling to find books on such things. Cheers |
| MagicSmoker:
--- Quote from: Glenn0010 on July 25, 2019, 06:45:26 pm ---... I have already designed gate drives before for my bachelors thesis so I have a pretty good grasp of things. However I want to do the best job possible. Further more in the past we have run into some issues during short circuit testing so I'd like gather more information on how these can be sorted from the onset. --- End quote --- Surely ("and don't call me Shirley"*) you realize this is rather open-ended - there's a wide range of gate drive designs of varying complexity w/r/t isolation voltage, power level, budget, switching speed, whether multiple switches will be operated in parallel (or, much less commonly, in series), whether dynamic current (or voltage) sharing is required in parallel (or serial) operation, hard-switched - so considerable Miller effect - or (quasi-)resonant, etc. That said, the default desaturation threshold in many commercial IGBT gate driver ICs is around 7V which is almost always too high to save the IGBT when it is triggered; knocking a couple volts off that and setting the gate voltage when on to around 12-13V, instead of 15V, can improve the odds of surviving a hard short greatly (for NPT IGBTs, anyway; all bets are off with PT types). --- Quote from: Glenn0010 on July 25, 2019, 06:45:26 pm ---Are there any good books which talk specifically about IGBTs, FETs and gate drives. Things such as the Kirk effect and so on. --- End quote --- Not that go into any great detail, but plenty of app notes floating around the interwebz on this subject. I haven't thought about Kirk effect in years, but I do recall it is a property of semiconductor device physics and therefore not something you can do anything about. * - 2 points to anyone who recognizes that classic quote |
| Glenn0010:
--- Quote from: MagicSmoker on July 25, 2019, 08:04:39 pm --- --- Quote from: Glenn0010 on July 25, 2019, 06:45:26 pm ---... I have already designed gate drives before for my bachelors thesis so I have a pretty good grasp of things. However I want to do the best job possible. Further more in the past we have run into some issues during short circuit testing so I'd like gather more information on how these can be sorted from the onset. --- End quote --- Surely ("and don't call me Shirley"*) you realize this is rather open-ended - there's a wide range of gate drive designs of varying complexity w/r/t isolation voltage, power level, budget, switching speed, whether multiple switches will be operated in parallel (or, much less commonly, in series), whether dynamic current (or voltage) sharing is required in parallel (or serial) operation, hard-switched - so considerable Miller effect - or (quasi-)resonant, etc. That said, the default desaturation threshold in many commercial IGBT gate driver ICs is around 7V which is almost always too high to save the IGBT when it is triggered; knocking a couple volts off that and setting the gate voltage when on to around 12-13V, instead of 15V, can improve the odds of surviving a hard short greatly (for NPT IGBTs, anyway; all bets are off with PT types). --- Quote from: Glenn0010 on July 25, 2019, 06:45:26 pm ---Are there any good books which talk specifically about IGBTs, FETs and gate drives. Things such as the Kirk effect and so on. --- End quote --- Not that go into any great detail, but plenty of app notes floating around the interwebz on this subject. I haven't thought about Kirk effect in years, but I do recall it is a property of semiconductor device physics and therefore not something you can do anything about. * - 2 points to anyone who recognizes that classic quote --- End quote --- With regards to the short circuit , what we have experienced is not failures as most industrial IGBTs are short circuit rated for about 10us, less with the newer ones. What we have experienced are oscillations when we try to turn them off, and we think that the kirk effect is playing a role. The way I see it, if I can better understand the nuances I might design the drive in a way where it negates and issues. |
| T3sl4co1l:
I'm not aware of any mechanism where the Kirk effect, by itself, can become active (oscillatory), rather than passive (dissipative, slowing). More likely you've had dV/dt or EMI causing feedback in the driver? Like, one discrete driver I tested, I saw this: Inverter output voltage (inductive load, distinctive step due to diode to IGBT conduction) Zoom on the falling edge. Very bouncy. Not due to inverter strays! A different configuration, I don't remember what; triggered by coupling between drivers, maybe? I changed to a more conventional architecture, with better isolators (SFH6345), problem gone. Incidentally, I've always used desat detectors in my circuits, and have burned two handfuls of transistors my entire career. One of those being a quad IGBT module, which is kind of unfair compared to the size of hands, mind. Regarding short circuit behavior, one test we did was with one of those quad modules (1200V 300A per transistor, I think?), where we observed a peak up to 6kA or so, with successful turn-off and no damage. Those modules were EOL at the time already; they handled this just fine. I would be shocked if any IGBTs being made today suffer from turn-off problems. (Hm, at least those in the 1200V range. I could see medium-voltage parts managing to be harder to use, but don't know offhand.) --- Quote from: MagicSmoker on July 25, 2019, 08:04:39 pm ---That said, the default desaturation threshold in many commercial IGBT gate driver ICs is around 7V which is almost always too high to save the IGBT when it is triggered; knocking a couple volts off that and setting the gate voltage when on to around 12-13V, instead of 15V, can improve the odds of surviving a hard short greatly (for NPT IGBTs, anyway; all bets are off with PT types). --- End quote --- Irrelevant. It takes roughly another three nanoseconds for Vce to rise from 7V to 15V, once the desat current is reached. High desat thresholds are handy for systems integrating MOSFETs and IGBTs as assembly options; we also did that, where we used IGBTs for a low frequency power supply and MOSFETs for a high frequency supply. The 900V MOSFETs available at the time had a generous Vds(sat), necessitating a desat threshold something like 50V. (Desat isn't always employed, or suggested, for MOSFETs, but it works just the same, and prevented short-circuit failures in the system quite well.) P.S. I picked the wrong day to stop sniffing rosin fumes. Tim |
| MagicSmoker:
--- Quote from: T3sl4co1l on July 25, 2019, 10:15:42 pm ---I'm not aware of any mechanism where the Kirk effect, by itself, can become active (oscillatory), rather than passive (dissipative, slowing). --- End quote --- I really only had the vaguest recollection that Kirk effect had something to do with bipolar devices, much less recall what it actually was, but a quick search refreshed my glue-addled memory. Basically, it is a massive increase in the time it takes charge carriers to transit the die at high current densities, and so it seems plausible that if the current reached into the zone where Kirk effect reared its ugly head that that could cause the on state voltage to increase which could cause current to drop which could reduce the Kirk effect causing current to once again increase, etc., and so on. But, again, this is more physics than engineering, per se. --- Quote from: T3sl4co1l on July 25, 2019, 10:15:42 pm ---Irrelevant. It takes roughly another three nanoseconds for Vce to rise from 7V to 15V, once the desat current is reached. --- End quote --- I suspect you are assuming desaturation as a result of a cross-conduction type of failure, rather than a short in an external load (e.g., a motor or the primary of a transformer whose secondary is shorted)? --- Quote from: T3sl4co1l on July 25, 2019, 10:15:42 pm ---P.S. I picked the wrong day to stop sniffing rosin fumes. --- End quote --- 2 Points!!! :clap: |
| Navigation |
| Message Index |
| Next page |