MC3334 based ignition

[Rich M]

Hi Guys,
A normal bipolar would have Vce(sat) around 0.7V, but not a darlington!
MJ10012 quotes Vce(sat)=2V at Ic=6A, Ib=0.6A and Vb=2.5V - that's 1.6Watts
dissipation just for base drive!

How about a IGBT? Look at Motorola MGP20N40CL - Vce=400V (internally
clamped), Ic=20A cont. Vce(sat)=1.8V max.(at 10A)  Gate drive is like a
logic-level mosfet ie. guaranteed fully on at TTL logic high(min) level,
gate current is statically negligible, but highish gate capacitance requires
a reasonably stiff drive for high speed switching. The gate is zener clamped
to avoid damage from voltage spikes.
This device was designed for coil switching and all in a TO220 package
style.
www.mot-sps.com for details.
Hope this helps.

Rich

> -----Original Message-----
> From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
> Behalf Of rr
> Sent: 16 February 2000 02:26
> To: diy_efi at diy-efi.org
> Subject: Re: MC3334 based ignition
>
>
>
> The problem with a high-voltage MOSFET is the RDSon. The
> losses can be higher than expected. And they are expensive.
>
> Figure at 5-amps current and 0.4-ohm RDS, that's a 2-volt
> drop across the switch. A bipolar will be about 0.7-volts.
>
> BobR.
>

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