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Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Hello!
I am having some problems with my IGBT driver, and I was hoping you people could help, as I have not been able to solve it on my own.
My IGBT driver circuit is unable to switch my IGBTs on when the voltage between the collector and emitter is above ~100V. I looked at the turn-on pulse from the IC (pin 6 & 7), and it became more and more noisy the higher Vce on the IGBTs was, and when it was above ~100V, it disappeared.
Here you can see my schematic (nevermind the wrong name on the IC). The IGBT driver IC is connected to two parallel IGBTs, that control the current for a coil (this is for a coilgun). When the electrolytic capacitor C is charged to over ~100V, the IGBTs will not turn on. They are rated for 1200V.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Did you see if the igbt gates will hold a charge at that voltage? Try them one at a time to check if one is leaky or something. Plus this won't affect the gates turning on or not, but if you parallel igbts you need a gate resistor for each gate. Just to reduce ringing and match the switching more accurately.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
I have not tested that, no. How would I do that? Replace the coil in my circuit diagram with a high-ohm resistor and try to turn the IGBTs on without using the driver circuit?
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
from what i can see from the Driver IC Datasheet, it already has a internal 100k pull up resistor. other then that i cant see anything wrong with it and ive been sitting here and looking at that schematic for a while.
Registered Member #242
Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210
Whats the 9V supply voltage look like? Might need to add some capacitance near by since the gates can pull a big slug of current when switched on. Can it drive a single igbt?
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Jrz126 wrote ...
Whats the 9V supply voltage look like? Might need to add some capacitance near by since the gates can pull a big slug of current when switched on. Can it drive a single igbt?
No, removing one of the igbts did nothing. It still will not fire properly above 100V. The 9V power supply is able to deliver 1.2 amps, so it should be enough. It works for low Vce, like 40V.
I also noted now that when I discharge the cap bank through a resistor, the IGBTs can turn on at Vce higher than 100V. But when I tried this, sizzling noises came from somewhere, I think it might have been my 9V power supply. It is all so strange...
Another point of interest: When I attempt to switch the igbts, and it doesn't work, the cap voltage drops rather rapidly (couple of volts per second). I can think of two possible reasons why this is happening: 1 - Current goes from the collector, into the gate, through the igbt driver IC, and to ground. 2 - The igbts are only slightly turned on, letting a small amount of current go through.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Dr. Dark Current wrote ...
2 is probably right. Measure the voltage of your 9V power supply. Also, an IGBT usually needs at least 12 volts to turn on fully.
I see. I should probably find a way to supply the driver with 15V then, as the datasheet recommends. I am not certain how I should to this, though. Is it possible to make a voltage doubler for DC?
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IGBT driver problems
