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Re: solid state coil problem
From: RODERICK MAXWELL[SMTP:tank-at-mail.magnolia-dot-net]
Reply To: tank-at-mail.magnolia-dot-net
Sent: Sunday, November 16, 1997 11:12 PM
To: Tesla List
Subject: Re: solid state coil problem
Tesla List wrote:
>
> From: Harri Suomalainen[SMTP:haba-at-cc.hut.fi]
> Sent: Friday, November 14, 1997 12:13 PM
> To: Tesla List
> Subject: Re: solid state coil problem
>
> On Thu, 13 Nov 1997, Tesla List wrote:
> [core saturation]
> > Thanks! That is probably the solution to my problem!
> >I don't have pin
> > #10 connected at all, which happens to be the shut down pin. I think
> > what I,ll do is use a 555 to shut down the both outputs at about 300hz
> > or lower. I may have to play around with the freq. and or the duty cycle
> > of the 555 for best results. Thanks!
>
> Shutting it down every now and then is not the solution! You need to
> shut the conducting fet during the conduction cycle prematurely if
> the core is getting saturated. It will not take many switching cyckles
> to saturate the core, usually a few will do the destruction. In worst
> case even a single pulse may saturate the core! You need *pulse-by-pulse*
> current limiting. Without one you will just pop the fets. Putting the
> system on and off every now and then at 300Hz or 10kHz or whatever is
> not the solution. It will help nothing.
I guess It's time to face the music. I neglected to look CLOSELY at
the documentation of the mosfet driver I was using. The driver that I
was using was a INVERTING driver! So when I turned the duty cycle down
on the pwm I was really turning it up! Boy do I feel dumb. This is at
least one of the reasons, If not the reason it was drawing to much
current.
I've ordered different drivers to solve the problem (HV400M)
NONINVERTING driver. They have a very high source/sink capability
(source 6A/ sink 30A) at a maximum of 300khz. I will have to use two of
course.
Frankensteins Helper
Max