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Re: solid state coil problem
From: bmack[SMTP:bmack-at-frontiernet-dot-net]
Sent: Thursday, November 13, 1997 8:42 PM
To: Tesla List
Subject: Re: solid state coil problem
> From: RODERICK MAXWELL [SMTP:tank-at-mail.magnolia-dot-net]
> Sent: Wednesday, November 12, 1997 7:12 PM
> To: Tesla List
> Subject: Re: solid state coil problem
>
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> " You may be right. The circuit does not seem to turn on until power
> supply voltage reaches 20vdc. I am using a simple series pass transistor
> voltage regulator to power the signal generator circuit. Apparently I
> should change the resistor in the regulator for a lower value so the
> transistor will switch on at a lower voltage."
>
Something is very wrong here. Are you checking this out with an
Oscilloscope?
My impression is that this system is drawing way too much current. In fact
it
sounds like one or both of your driver transistors are turned on in a dc
mode
(perhaps even shorted source-drain). In other words- it ain't oscillatin'.
Recheck your PWM for wiring errors. Also some of these devices have various
UVLO and overcurrent shutdown schemes that need to be properly biased even
if you're not using them.
Again, not being familair with the specifics, I hope you have a regulator
for the
PWM IC , most can't even take 20 volts!
> " Since I last posted this problem I have come up with at least a
> partial solution to the problem. I will parallel two or more transistors
> on each leg of the primary to compensate for the current draw,"
Don't do it until you know why it's drawing so much current!
If memory serves, you are using IRF740's. these are PULSE RATED at
something like 30 amps!
I
> Did you use magnetic design technics on this?
>
> " Nope."
Igor was a bad boy! this could be a problem.
>
> Jim M
>