RE: Solid-state coil (gate xfrmr question)

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

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>

Hello Carl,

Digikey has some SCR trigger transformers you could try.  They are expensive
($14 or $15), but you might consider them for your use.

Pete Komen

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, November 05, 2001 7:03 PM
To: tesla-at-pupman-dot-com
Subject: Re: Solid-state coil (gate xfrmr question)

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

Hi Carl,
         Siemens N27 or Philips 3C8(5) or 3F3 material will be OK for
the core. The winding inductances should be reasonably high to
minimize primary current and energy storage in the core. Note that
during the "on" period, primary current ramps up by: Ip = V.t/Lp
Doubling the number of turns quadruples Lp and drops Ip to 1/4 of
that value which halves N.Ip (magnetizing force) and quarters core
energy. You want good coupling between the primary and secondary
windings.
       You will need some resistance connected across the secondary
winding to drain what little energy there is. It's a good idea to
check the final result for spiking and adjust the resistance to
eliminate it before hooking the MOSFET up or disaster will strike.
       What is you supply voltage? Is the isolation barrier a
necessity?

Regards,
malcolm

On 5 Nov 2001, at 16:17, Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<cwillis-at-guilford.edu>
>
> Hi folks,
>
> I just started toying with a solid-state coil setup that uses an IRF740
> driven by a 556 timer and a gate driver chip.  The thing is working pretty
> well, giving up to 5" of spark with about 70 watts in.  I'm confused about
> one thing in particular, though- the problematic isolation transformers I
> made to protect the driver circuit in case the transistor dies.  I have
> made three of them now, all having about 12 turns on the primary and
> secondary around different ferrite toroids I had lying around.  All have
> the same effect of keeping the coil from putting out as big a spark as
when
> the gate is driven directly.  So, if you know what ferrite material to
> select for a core, how big to make it, and how many turns should be
> required, please let me know!
>
> By the way...a big thanks to Richie Burnett for putting a great tutorial
on
> MOSFET coils on his website- it is really all I have had to go on and I
> know it has saved me many a blown FET...at least so far I still have the
> "original" one in there.
>
> Carl
>
>
>
>