Re: KV's and multimeters

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: KV's and multimeters
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 23 Nov 1997 23:36:41 -0600
Approved: tesla-at-stic-dot-net

From: 	Edward V. Phillips[SMTP:ed-at-alumni.caltech.edu]
Sent: 	Sunday, November 23, 1997 12:13 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: KV's and multimeters

'Help!!!! The driver that I was talking about is now giving me seriuos
problems. I replaced the TV transistor with a 3055 and the voltage was, as
you said, increased, but the thing quit working. After trying a few things
I decided to try a new 555, and it worked again, but quit again."

	My guess is that the 3055's are experiencing collector to
base breakdown and that, if you are driving directly from the 555,
could lead to the 555's failure.  The voltage pulse on the collector
when you cut off the current can be at least as much as 600 volts
if you are really pounding the coil, and 3055's can't take anywhere
near that on a regular basis!!!  I was surprised when you mentioned
that you were using 3055's with some success!  The TV transistor you
were using was designed for as much as 1500 volts collector swing,
but may have had a pretty high "ON" resistance.

	Go back to the original transistor, or better yet to one
of the 800 volt IGBT's made by International Rectivier and others.
A buffer transistor between the 555 and the base of the switch
transistor might protect the 555's, but not the 3055's.  Wish
I had more time to comment, as I've built a number of quite
successful coil drivers over the past few years.

Ed