Re: DIY VFD Update

azotic wrote:
"Joseph Gwinn" <joegwinn@xxxxxxxxxxx> wrote in message news:joegwinn-69F4E1.17142916082008@xxxxxxxxxxxxxxxxxxxxxxxxxxx

In article <Mcqpk.38867$yn5.22137@xxxxxxxxxxxx>,

So each module is a a half-bridge containing two IGBTs plus some
frewheeling diodes. What make and model?

Joe Gwinn


I am using Toshiba MG100Q2Y51A GTR modules.

Intresting project your working on, there are IGBTs that might work
for your application but there going to be pricey. I did see some 600 amp
IGBTs on ebay this week that were reasonably priced. If your going to
buy some on ebay make shure you ask the seller if you can return them
should they be blown. Some sellers are selling units they claim are tested
but they are not. I had to return some that had blown gates and would not
fully turn off.
Joe is right, IGBTs are not well suited to high current pulses. You have to keep them fully saturated, or the current hogs to the hottest part of the die, in a positive-feedback death spiral. The design of the FET to BJT drive scheme built into the transistor only allows so much base drive. SCRs are better at this, as increasing current increases drive to the internal transistor-like structures it is built from. You could also use a bank of parallel MOSFETs, although the 350 V supply requires using more of them. MOSFETs are so cheap, you might be able to buy a couple dozen new for what a used monster SCR or BJT would run you surplus. MOSFETs are quite tolerant of pulse overloads, too.

Jon
.

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