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Re: hvguy-dot-com new flyback driver

Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>


> SCHEMATICS and info of our new driver can be found at www.hvguy-dot-com,
> at the very top, just under the blue laser title pic.
Looks nice! :) And seems to work quite well too!!!

Hey, I got an additional tip (==cost reduction) for the gate drive: you
can use a single CD4049 (hex inverter, costs maybe 10 cents??) to replace
the four transistors in the gate drive.

It works stunningly well for this single mosfet drive, and the gate
signal looks superbly clean. Just connect a couple of outputs from your
CD4049 together, and connect the mosfet gate to them.

(I use a setup exactly like that to drive four 20V mosfets that in
their turn drive a beefy gate drive transformer. Works beautifully.)

One question about the protection diodes around the mosfet: what are they
for? I may be mistaken but I thought that the voltage spike on the mosfet
is always positive (ok I never measured...), so the mosfet intrinsic
diode/bipolar transistor never conducts, thus, doesn't need to be
disabled?  ;o) You could save some bucks by leaving out the FR and
schottky diodes? Or?

A reverse diode accross the flyback primary helps hugely agains voltage
spikes, but, it will get a bit hot so a heat sink is necessary. Some 
TO-220 packaged ultrafast diode would be best for this.
It's called a "flyback diode" in this flyback transformer setup.

Umm yeah and a final note: arcs from flybacks with internal rectifier +
cap are by far the longest. 6-7cm. It's sure worth trying out! :)

 - Jan

 high voltage at http://www.hut.fi/~jwagner/tesla