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Registered Member #8558
Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57
So i got a mini Tesla coil running based on Steve wards design but i have had the mosfets blow up when run at full power. I found these igbt's and they seem like they would work as a higher power replacement but i am not quite sure. They do seem to be cheaper here at 1-3$ ea than digi-key or eBay so i was wondering if they are a good deal or am i missing something obvious?
Those seem like nice fast IGBTs, low input capacitance too. However, you really need to know the cause of the MOSFET deaths in order to determine if these will do better. Bridge layout could be the culprit, in which case these may not fare any better. I'd give them a go though, as long as your switching speed isn't way out of line of what one would subject an IGBT to.
Registered Member #8558
Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57
I think the problem was interference in the interrupter because it would start to crackle at about half power when i was scoping the interrupter but when i took the probe off it stopped. The only time it killed the mosfets was running at 170v bus with 200v mosfets and striking to a grounded object. So if i use these then i should be able to run it with a voltage doubler without changing anything else as long as the caps are rated for it? Also from the data sheet the worst switching time i could find was 170 off and 160 on at 150C which is still over 3mhz so that should be good for a Tesla coil running in the hundreds of kHz range? Sorry for all the questions, i am fairly new to electronics.
Determining max switching speed is not as straightforward as one would hope. I have a thread about it in the general section. The method I use to determine what is too fast is detailed there, I can't claim that it is necessarily correct, but it does work for me.
Registered Member #8558
Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57
From that it looks like they should work. They are fairly cheap so i ordered some and will try it. But what is RthJC and RthCK on the data sheet? is that the maximum power dissipation or something as i would think it could switch at dc 36kw (60amps at 600v). Also why would the on delay and off delay limit the frequency to 10% of their value, the IGBT is still on or off during those times so unless i am mistaken the IGBT is only in the linear region during the rise and fall time so it would only be dissipating a lot of power during those times which would be 130ns worst case so if we limit that to 10% of the time it would be 750khz?
The off delay plays a role in cross-conduction unless you're using single-ended topology. I toss in the on delay as an added buffer, and again 10% is arbitrarily picked, but it has always worked subjectively in anecdotal evidence (haha). Keep in mind your bundled diode reverse recover time, if using a igbt with one, or a fet. Ideally you should isolate body and package diodes with a series drain side schottky and add another one antiparallel with the D/S / C/E junction.
Registered Member #8558
Joined: Thu Dec 06 2012, 11:38PM
Location: usa
Posts: 57
So do i need external diodes for these? I am not seeing any built in ones on the data sheet so i guess i will need to buy them separately. What kind of diode should is use for this? would a MUR1560 work?
Ya those should be fine, I use MUR860. You need freewheeling diodes whenever there is dead time to prevent back EMF from killing your silicon. Likewise body diodes are terrible and should be bypassed always, preferably isolated as well, but if your switching speed is low enough then isolation isn't necessary.
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Cheap IGBT for mini tesla coil IXGH 32N60C ?
