Re: Would Snubbers Kill Ignition Coil Output? (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 15 Dec 2003 14:51:48 -0600
From: Dr. Resonance <resonance@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Would Snubbers Kill Ignition Coil Output? (fwd)


There is a special chip mfg by International Rectifier especially for this
application.  It has all the snubbers necessary included in the chip.  It's
made for driving ignition coils.  I've used it and it works great!

It's a IGBT IR p/n IRGB14C40L.  Get the data sheets for these from IR.
Rated 20 Amps continuous collector current.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913
>
> Thinking of putting electronic ignition on my aged Massey Ferguson
tractor -
> discretely of course, don't want to spoil the look of the thing.
>
> Just fiddling around with the components that I've got, I have some
IRF748V
> HEXFETS, which look ideal for the job of switching, having a TINY
R{DS(on)}.
>
> Only problem is that they are only rated up to 60V.  This is fine for the
sort
> of voltages that I would expect to find around the tractor, but I'm rather
> concerned about the magnitude of the back-EMF from the ignition coil.
>
> My thought would be to put in a snubber with RC in parallel in series with
a
> diode (I've got some nice hefty TO220-style SMPS diodes).
>
> However, would putting the snubber in kill the output of the coil and not
leave
> me enough to fire the plug?  My documentation is all SMPS stuff and
doesn't
> cover this type of core arrangement, so I'm not sure what's going on in
there.
> Does it act like a flyback with the mother and father of all airgaps?
>
> The idea was to have the points pulse a 555 in monostable mode, putting
out a
> 900ns pulse, driving the MOSFET via a totem-pole arrangement to speed up
the
> switching.  (The idea being to cut down losses and stop the thing getting
too
> darned hot.)
>
> Cheers
>
> M
>
>
> --
> Matthew Smith
> Kadina Business Consultancy
> South Australia
> http://www.kbc.net.au
>
>
>