[PSIG]

Thank you David. Can you elaborate on the "Bootstrap with N-channel" method? I'm not sure I understand how you mean.

Oversimplified, an N-channel device (MOSFET, IGBT, NPN transistor, etc) is normally used low-side to switch grounding of a component such as the ignition coil. However, N-channel devices are perfectly happy driving on the high-side feeding the component, are less expensive, and cheaper for devices of equivalent rating. Also, some like the IGBTs are very difficult to find P-channel equivalents.

The issue is simple in that a high-side N-channel device needs a trigger signal higher than the supply voltage. So "bootstrapping" is simply giving the gate that higher voltage. For example, a logic-level MOSFET needs +5V to fully turn on. On the high-side, this means a system supply voltage of 15V will need a 20V signal to turn it on (5V higher than supply). That's what bootstraps do, even allowing you to use devices such as OEM ignition modules to control a coil from the battery(+) side of the coil.

More info on bootstraps here, and an example generic driver setup is here.

I have drafted a design of a CDI driving circuit with a thyristor. I will post it further down.

Keep in-mind that you would replace the entire stock CDI module with your circuits, and that the stock trigger must not trigger before the least advance desired at any time. Some systems trigger at high advance and the box retards it, and others trigger at minimum (cranking) advance and the box advances it, while some do both depending on which trigger edge is selected by the box (crank or run). I don't know which yours does, but you need to know or verify if you're going to also connect the factory trigger pulse into your circuits.

I think i COULD rewire and control it low side, but would like to be able to keep the wiring a stock as possible to be back compatible with the OEM system.

It should be a simple matter of disconnecting at one end of the coil ground wire or the other, and inserting your coil driver inline. You could also add a jumper connector or 'switch' to select the driver into or out-of the circuit (no cutting or mods), depending on whether you're running the stock CDI box or Speeduino. Just throwing ideas out there.

David

[tobbera]

Wow. You totally blew my mind just now. You mean I can use N-channel IGBT as a High-Side switch?

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