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Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Im about to build brick coil with relatively expensive transistors (1200V 6th generation semikrons) which i really dont want to break. So far im going to do these things:
- phase lead driver for getting rid of phase lag and those nasty reverse recovery spikes - series-parallel lytics and transistors in dc bus coupled together with laminated busbar - 1-2x ultra low impedance 20uF film caps bolted right on the transistors. - 24V gate drive, 33V bipolar TVS diodes over gates - keep all things grounded, tie dc bus negative to mains ground with capacitor (100n?)
These things are quite obvious but is there anything else worth of doing?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Kizmo wrote ...
Im about to build brick coil with relatively expensive transistors (1200V 6th generation semikrons) which i really dont want to break. So far im going to do these things:
- phase lead driver for getting rid of phase lag and those nasty reverse recovery spikes - series-parallel lytics and transistors in dc bus coupled together with laminated busbar - 1-2x ultra low impedance 20uF film caps bolted right on the transistors. - 24V gate drive, 33V bipolar TVS diodes over gates - keep all things grounded, tie dc bus negative to mains ground with capacitor (100n?)
These things are quite obvious but is there anything else worth of doing?
24V gate drive is not gonna be healthy for your bricks on the long run :P Also, don't forget to TVS the bridge.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Sure the expected life will go down more or less but there are some reasons why we drive gates this hard. And in the past even harder (i have seen 30V gate drives..)
Also i have heard that tvs strings over collector-emitter are waste of silicon? Sure i could put 800V strings there. Bus voltage will be 565V
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Another reason why driving the gates at 24V may not be the best idea - At 24V drive your short circuit withstand time with be significantly lower due to the channel dropping less voltage. It may be wise in your case to use 15V drive given you don't really need the speed bonus from driving the gates hard. The gen 6 semikrons with phase lead should operate fine up to 100KHz or so with 15V gate drive.
Another option that I have looked into but never tried myself is the "desaturation detector" generally you do this by looking at the voltage from C to E and shutting of the gate in the event it falls out of an acceptable range. attached is a good writeup on the topic from a couple years back. Google also has lots of info on the topic.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Thanks Eric that paper is truly helpful.
Coil in question will be operating at mid 40kHz so igbt speed wont be problem at all. These new semikrons seem to have such a low self inductance that even without phase lead their rinding during hard-ish swithing is very small compared to older bricks. My minidr uses -128D semikrons without phase lead at 100kHz and there is hardly any ringing/overshoot to worry about even though it is switching ~560ns late
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Same goes with collector current. According to some Semikron guys the pulsed collector current value should not be exceeded under any circumstances.. and yet still we do it. Its all about how long life we want out of these things. When used within spec these things will last almost for ever :)
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Well, used transistor should always be treated like used transistors. I test mine with HV applied over C-E to see their actual breakdown voltage. Healthy 1200V device cannot break down at less than 1200V.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Good idea. I use a variac, MOT and high value wirewound resistor to carefully apply high voltage, and a 100x scope probe to watch the C-E voltage.
Healthy devices just clip the peaks like a zener diode, a few hundred volts above their rating. While testing surplus IGBTs, I found some with enough gate leakage to make them oscillate violently and smoke the resistor.
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DRSSTC transistor protection
