Re: [TCML] flyback driver sucess.

[Michael Twieg <mdt24@xxxxxxxx>]

On Thu, Oct 27, 2011 at 12:28 AM, Scott Bogard <sdbogard@xxxxxxxxx> wrote:

> Greetings all.
>     OK, I successfully got my ARduino based flyback driver up and running,
> so I have variable frequency and duty cycle.  Trouble is it only lasted a
> few minutes, I left the room, came back (with a plasma globe to test) and it
> was a fuming pile of melted wire on the floor.  My question is why did this
> happen, I figure the FET must have shorted, but I am not sure why.  Here is
> the setup.  ARduino as PWM square wave generator, to optocoupler through
> some resistor (3 470's in parallel) from optocoupler (fed off of 18V
> regulated) into gate of FET.  I did not use gate resistors, perhaps that
> would have been a good idea?

Do you mean an optocoupled FET driver, or just a plain phototransistor
optocoupler?  If possible give us a schematic.

>  Also I believe it was pumping out 18V on the output, is that too much
> voltage to drive a gate, I believe they are 5V gates...

It's possible, but most power FETs can handle gate voltages of 20V at least,
even if their threshold is a lot lower.  You'd have to check your datasheet
to be sure.

Another possibility is that you exceed the drain voltage the FET can
handle.  You'll probably want a clamp on the primary side, and maybe some
kind of snubber as well.  And you could have just given it more current than
it could handle.  Anythings feasible, but it's hard to be sure without some
hard numbers to go on.

-Mike
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