[Diy_efi] MC3334

[Keith Ballantyne]

I was going to use that chip until I learned how hard they are to get.
I switched to simply connecting my coil drivers directly to ISL9V3040D3S
parts from Fairchild.

Keith Ballantyne

> Sent: Thursday, September 12, 2002 9:57 AM
> To: diy_efi at diy-efi.org
> Subject: [Diy_efi] MC3334
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> I am currently working on a very simple ignition module based on the
> MC3334 High Energy Ignition Coil Driver,from Motorola.This is a
> rather old chip,in fact,Motorola has taken the datasheet away from its
> intranet,but I know for sure that the chip is still in production.They
> sent
> me the datasheet.
> I am driving a 4 mH primary ignition coil with a IRF740 mosfet on an
> aluminium heatsink big enough to fit on one side of the
distributor,and
> 50% dwell time from an inductive 50 Hz signal (which represents 750
rpm
> in a 4 cylinder engine).
> The mosfet is getting too hot after 3 minutes of switching.
> Current peak : 5,3 A
> Reverse voltage peak : 320 V
> Dwell time : 51 %
> Captor inductive : 5o Hz sinusoidal signal.
> The IRF740 is set in conduction through a 200 ohms 5 watts resistor
> from a 12 Volt bat.,and the MC3334 pulls the gate down to shut it off
> at the end of the dwell time(roughly 10 ms at 50 Hz),to induce the
> magnetic
> field on the secondary winding of the coil,connected to the plug which
> will
> produce the spark,and keeps it shut off untill the next
> captor signall is received.
> But a IRF740 drain scope read shows that what should be a fairly flat
line
> (or a mild upward slope to 0,2 Volts)at ground level for the first
couple
> of
> milliseconds of the dwell time,shows an upward slope from ground to
1,5
> volts,which I believe springs from the fact that the IRF740 is not in
full
> conduction,therefore,getting hot.
> Has anyone built a project on this chip?
> I will appreciate any help I gan get.
> Thanks in advance.
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