VND5N07 for coil driver?

[billr]

With a 5A max current rating, are those too light to use as coil drivers for COP-type coils? I'm pretty sure the old single-coils for dizzy use drew more than 5A, but maybe not the smaller COP coils? I'm wondering if the the injector drivers on an MS3X board could be used as coil drivers by just making a couple of special (but simple) cables for connecting the MS3 to MS3X; and that would be assuming you were already using P&H injector drivers so the on-board MS3X injector drivers aren't being used.

[racingmini_mtl]

The issue is not only the current rating but also the voltage rating. The ignition IGBTs are rated at around 400V breakdown voltage compared to the 70V for the injector drivers.

Jean

[billr]

For a reliable install I can see that a high voltage rating for the ignition is a proper recommendation; however, with a good flyback clamp, do the spikes on the coil primary really go that high? I'm thinking my coil drivers are something like a TIP125.

[ekam99]

As mentioned, you need a high voltage transistor which also has a good energy capacity. HV spark is based on a ratio of a coil. Typically ~80.
If one clamps on 70V, it has no more than (ideally) 5600 volt.

[Peter Florance]

You need the high voltage spike. Otherwise, no good spark. I doubt your coil drivers are TIP125. For one thing, they are PNP devices.

[elaw]

^^ What he said!

The primary voltage in a coil mirrors the secondary voltage. Clamping the spike on the primary side will have the effect of clamping the secondary, which would not be a good thing.

Also COPs can draw plenty of current... the VAG ones I'm using peak at about 12A. The duty cycle is less, but the peak current draw is as much as a regular coil.

[billr]

Okay, I get the message! I meant "TIP-125 family", whatever the NPN variant is, by the way. Some day I will have the ignition driver module off and opened up again, I'll satisfy my curiousity about it then...