Re: hvguy-dot-com new flyback driver

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

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

Hi!

> 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.
  http://student.fortlewis.edu/~gwdurland/4049.html

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! :)

cheers,
 - Jan

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