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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Hi all I going to make DRSSTC, but i don't want to blow bridge, so i need lot of protection.So i decided to make CT protection, and Vsat(ce) protection... The biggest problem need block 300Vdc, and let go just 2,5V (from open IGBT) and here is my idea...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You don't need the MOSFET, just a HV fast recovery diode, with its cathode to the IGBT collector, and a pull-up resistor to the rail on the LM311's input.
When the IGBT is on, the diode will conduct and pull the LM311's input down to Vce(sat)+0.7V.
When the IGBT turns off, the diode will be reverse biased and block the high voltage. The reverse recovery spike will hit the LM311's input, so it's vital to use the smallest, fastest diode you can find. The zener on the input will help to absorb it too.
This isn't my idea, I saw it in a schematic for some inverter somewhere, but I can't remember where.
Also, you probably want to work on your logic, what you have there will probably make the IGBT oscillate on and off at high frequency, and the switching losses will destroy it instantly. A better idea would be a 555 timer or whatever, to lock the whole H-bridge out for a second or two.
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IGBT protection
