Re: SCR coil questions..was Sam's HIGH POWER...

>Date: Tue, 19 Jan 1999 12:07:01 -0700
>To: tesla-at-pupman-dot-com
>Subject: Re: Sam's HIGH POWER Ignition Coil Driver. Record pulses,
>  driver  dead:-(
>From: Tesla List <tesla-at-pupman-dot-com>
>Original Poster: Eddie Burwell <eburwell-at-HIWAAY-dot-net> 
>> Does anyone have a good diagram for a SCR trigger circuit that will
>>trigger larger SCRs (I have a 20mA gate current one now, moving onto
>>100mA gate current) at a wide, adjustable frequency range?
>Check out http://home.HIWAAY-dot-net/~eburwell 
> This circuit as shown was delivering about 2000ma peak into the gate. 
>just upped that on my prototype probably to about 4000ma. This is the 
>max peak   gate current for my SCR.
>If you have questions about this circuit feel free to ask!
>OK, I will!
Have you ever 'scoped the primary waveform? That 2 us current rise
is probably pure wasted energy, drawing on the power supply and   
doing some strange things with the primary tuning until it all
slams into full conduction. I was wondering if any ringing occurred
at all during this interval?

Scr's are intrinsically slow devices, so one may consider that the
primary reverse time may NOT be sufficient to turn the SCR off!
Perhaps the reactor comming out of saturation is what shuts it down.

Most diodes have a non repetative surge rating, which means that
the device can take maybe ten times the operating current upon some
event such as power up into a capacitve load. The key phrase here
is NON REPETATIVE. What kind of life do you get from your 80A SCR
pumping 1000 amps?

Hopefully your mystery diode is some high current "fast" type,
otherwise it will experience catastophic failure due to its 
not comming out of conduction fast enough(reverse recovery). Seems to
me that this one is MUCH more vulnerable than the SCR since it has
no large inductor to protect it.

Last question. Do you run the coil that close to your computer?

Jim McVey

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