Re: Driving circuit FET problem

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi George,

On 5 Dec 2002, at 8:16, Tesla list wrote:

 > Original poster: "george hadle by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <ckreol1-at-yahoo-dot-com>
 >
 > hi, My driver circuit its an ignition coil driven by a
 > FET protected by schottky diodes.
 > The problem has several symptoms, all independent of
 > the TC being connected or not.
 > If I short the hv terminal to ground, the circuit
 > completely ceases output.  It can spark between these
 > two terminals without problem, its only when directly
 > shorted it messes up. Whether the output is latched ON
 > or cut OFF, I think its latched ON.
 > I'm running it at audio freq. and the sound of the
 > coil completely stops.
 >
 > I can rectify the problem for a few seconds one of two
 > ways.  Turning off and back on.  Or changing the
 > frequency of the FET driver, which is a schmitt
 > trigger oscillator.
 > any ideas?

 >From the symptoms I'd say the supply is self-oscillating (Y-N)? If
so, running it from a separate oscillator will definitely get around
this problem. Modifying the existing circuit will also work in some
cases.

Regards,
Malcolm