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Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
I wonder how good that PLL would work with a small DRSSTC. It's so simple. Since its got a constant wave output so you can sync the interupter with the Freq out.
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
Linas, should you show oscillograms of both gates at load? There are no any ringings? I see you don't use damping resistors for gates, so I'm trying with it.
If you want to use external diodes (MUR860), you need to block the IRFP460's internal ones. To do this, place more diodes or Schottkies between MUR860's cathodes and IRFP460's drains, like as in this scheme: (the blocking diodes are 1N5822)
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
I don't use block diode, but i think is nessesary. so i use gate resistor (5om) scheme is hiere,how i connect rezistor, cap and oscilloscope cap and frequency is same (20nF and ,350KHz )
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
I'm asking about gate waveforms at real load - with real load I mean powered half-bridge and IRFP460 instead of 20nF capacitor. Applying current to drain changes waveform, since there's capacitance between gate and drain. I may be wrong, but you probably drive Tesla coil with lower frequency than 350kHz, right?
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
yes, the Fr is 342KHz, but then i use bigger toroid then Fr is 300KHz.. and i don't have any mosfets, tomorrow i am going to buy IRF460, but i think, i have alredy bay all mosfets in my city (IRFP460 cost is 7Lt, in other shops 14LT and more ,2.7LT=1$)
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
I have found interesting information there:
See the blue comparison table. You can see that internal diode must be disabled, otherwise transistor will blow up. Hope this is reason why you have so much breakdowns.
By the way, it's better to buy a package of cheap MOSFETs and use them for testing/tuning purpose than being continously sorry for blown and pricely transistors, like IRFP460's.
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Mosfet's protection
(IRFP460 cost is 7Lt, in other shops 14LT and more ,2.7LT=1$)