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Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
I just tested my driver and well, after a few tests it exploded…
It is full bridge, but I used only a half of it for initial testing. The drive signal was 50% duty cycle square wave, at 50kHz. IGBTs were drive thru driver IC, with bootstrap.
At first I tested it with no load and it gave a square wave on the output going from -165 to +165V.
Then I connected my transformer thru inductor and capacitor, transformer produced an arc for a fraction of a second and 2 igbts were gone.
Then I took inductor and a capacitor and transformer form Chinese power supply which was using a half bridge pwm driver. Powered up igbt section, turned on a squarewave. Only one spark in the beginning, turned off a signal and after a second, something happens and it starts arcing… One more time, same thing… Its like something happens to the drive signal when my logic PS turns off and does something on the last breath.
Disconnected transformer, hooked up oscilloscope to the output, powered up igbts, turned on the logic and boom!!!
Have no idea what could happen, igbts were gone, pcb traces were molten, all the resistors in the gate drive circuit were burned open!!!
I havnt used heatsinks on igbts because I turned the device on for less than 5 seconds every time.
Oh yeah, and I turned on the logic with oscilloscope connected, before i did it over way around. Exactly the same setup worked (except for the time when oscilloscope was connected) and suddenly it explodes???
Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
Its almost 5 am and I am still working on it, what the freak? I think explosion occurred because of oscilloscope, I probably hooked up a ground clip to the output. And since it was all connected to the same ground, it effectively shorted the circuit.
It is making more sense now after I found out my GFI powering up a router turned off in garage. Short must have affected it somehow and caused a ground leak in the electrical system.
But I still cant find out why is that weird behavior with turning off logic occurs??? And why its not working when its just on?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well, I also had some unexplained bridge explosions with bootstrap drivers, but these were not due to any shorts, they were due to the nature of the driver and forward characteristics of the bridge clamping diodes.
When the bridge output transitions from high to low driving an inductive load, a spike of several volts can be induced on the lower clamping diode (if it's not ultrafast soft recovery one designed to clamp fast high current spikes). Now there are 2 mechanisms that are possibly responsible for the driver death: 1) The bootstrap supply gets charged to dangerously high voltages (20+ volts) because of the spike and either the bootstrap drive or transistor gate are damaged. 2) The driver does not like getting the bootstrap negative voltage below low-side ground, in which case I've measured that both outputs can go HIGH at the same time, leading to ultimate destruction/ explosion of the bridge.
Since I started to use GDTs, I've not had any unexplained destructions anymore.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Connecting an oscilloscope to a floating circuit is a very basic error... If you really want to do this, you can disconnect the ground pin of the oscilloscope power cord, but this is very dangerous. Using two probes and subtracting the signals is the correct procedure. When turning on these circuits for the first time, add a lamp in series with the power supply.
Also @ Dr Kilovolt: where did you get your gas discharge tubes? All the tubes on digikey at low voltages cost quite a bit and only with orders of 20+...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
aonomus wrote ...
Also @ Dr Kilovolt: where did you get your gas discharge tubes? All the tubes on digikey at low voltages cost quite a bit and only with orders of 20+...
That was a misunderstanding, I meant GDT=Gate Drive Transformer, that's what I thought someone on this forum would think of first when he sees "GDT"
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Oh... lol ignore me then I made some connection between voltage spikes and discharge tubes... that, and I was just packing up some 130VAC rated tubes in my 'misc' bin....
Registered Member #1596
Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65
Oscilloscope clip short was the most impressive destruction, igbts cracked, their leads melted and pcb traces vaporized.
But my drive keeps failing at the load, I guess it does not like square wave and needs some more deadtime (driver IC has a 0.5us built in).
Digikey sent me the wrong ic for the logic controller and i am waiting for the replacement to arrive, after that i should be able to run it with any deadtime, duty cycle and frequency. I guess the drive did not like my impatience and desire to test it with oscillator only :)
Besides, i am thinking of switching to GDTs, it helps with insulation and illuminates optoisolators and separate isolated power supplies for logic/igbt drivers. With GDTs i should be able to have my ground planes at the same potential.
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Explosion!!! Smoke… destroyed driver… Please help!!!
