SSTC Related: Shottky Diodes Unnecessary!!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Justin Hays by way of Terry Fritz <teslalist-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi All,

I have recently been playing with several different SSTC setups. I
had a 2Mhz feedback coil going (tiny little thing), a TL494 400W
half-bridge one, and a H-bridge IRFP460 + 2kVA one going. So what's
the big deal? The big deal is, none of them use series shottky diodes
on the MOSFET drains!

My bud Aron left them out one day, "just to see" what would happen
and how they would affect waveforms. They didn't! Circuit operation
was identical with and without the shottkys. Aron was using 1N5821's
at the time (30V 3A). Neither I nor Aron has used shottkys
since...we're now leaving them to the low voltage power supply stuff
; )

The antiparallel diode's (the one across the MOSFET drain-source)
reverse recovery time (Trr) is critical. Make sure it's a "superfast"
type. And if for some reason, in ANY circuit, you have forward
current flowing through the diode immediately before it goes into
reverse recovery, it will increase the Trr dramatically so be careful
; )

For the superfast diodes, Aron and I are using FEP16JT's (50nS 16A
600V) for the high power stuff and EGP50K's (1kV 75nS 3A) for the low
power stuff. Use a diode that has a Trr of at least 100nS, a PIV
(peak reverse voltage) rating as same as the MOSFET's you're using,
and a current rating of just about anything. I like TO-220 packaged
diodes when used in a circuit running over 1kVA.

Making an H-bridge circuit board is EASY with no shottkys! You'll be
amazed at how much it simplifies the mechanical and electrical
design.

BTW, I found a great way to get 0-100% duty cycle control,
transformer-isolated gate drive ; ). This is wonderful for DC-AC
inverters, class-D audio amps, and other stuff requiring the gate
signals to be PWM'ed. Schematic and info coming soon on our website.

I Hope someone can benefit from the info, take care.

Justin Hays,
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com

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