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Registered Member #2680
Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45
I made a new board yesterday in hopes of using a pair of cm300DY-12E igbt modules for my DRSSTC, but i have no idea if i will be able to run them at a frequency between 80-90KHz(i could probably bring it down to below 80KHz). I tested out my driver and i get an okay waveform on the gate-emitter. I'm cautious on applying a voltage on the supply rails because the slow switch speeds on the igbts might cause a shoot-through. What is the best way to check the collector-emitter switching using an oscilloscope? -Dave
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
You can run the output bridge from a low voltage, e.g. 12V if you put a 1 Ohm resistor in series with the bridge supply you can't have more than 12A, which is nothing for a CM300. An 'ideal' place for the resistor is between the electrolytic(s) and the film capacitors (which are across the dc bus close to the transistors)
Registered Member #2680
Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45
Ok, i tested out 1 IGBT (i only have 1 board for 1 brick). So in theory, if my igbt was ideal, there should be no current draw because if CE1 is on, CE2 should be off and vice versa.
Here are the results: With 100V on the supply rail, and with 2.05 Ohms in series with the supply rail and the IGBT, the multimeter reads a current of 2.8mA. My oscilloscope saw a waveform (from 0V to 16V) at CE1 with a pulse width of 6.0uS when the input frequency was ~85Khz. Unfortunately, i have no idea what all this means :[
Registered Member #2680
Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45
Instead of using my multimeter to measure the current, i place my oscilloscope probe across the 2 ohm resistor. The yellow line is the probe across the resistor. The red one is the probe across the gate. If the peak to peak on the resistor is 100V, then the peak current is 20mA. I'm not sure if this is good or not:/
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
100V is a bit much for testing! But the fact that your resistor did not burst into flames is a good sign. Use a lower voltage next time, though.
Could you describe your setup with a little more detail? It sounds like you're testing one leg of an H-bridge, but 2.8mA of shoot-through sounds way too good to be true with a cm300 switching at 85kHz with 100V on the bus!
Registered Member #2680
Joined: Wed Feb 10 2010, 09:23PM
Location:
Posts: 45
I made an error in my calculations. While 2.8mA is the average current draw, the peak current draw is 50A which lasts for a few nanoseconds.
EDIT: I put a larger topload on and my resonant frequency fell from 83KHz to around 75KHz. The peak current through the 2 Ohm resistor i had in series seems to have dropped to around 7 to 8 Amps at 200V on the voltage rail. This is the peak current, the average current is less than 3mA.
Registered Member #333
Joined: Mon Mar 20 2006, 06:02PM
Location: Czech Republic
Posts: 45
You probably need more deadtime to eliminate cross conduction. Also be sure that your resistor is not much inductive otherwise you'll see bigger peaks than really are. Measuring with DMM says nothing...
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How can I safely test cm300s?
