simple "ignition amplifier" circuit for use on old vehicle with points
12 volts switched | | ______________|___________ | | | | / / to coil negative \\ \\ | /56k 2.2k / | \\ \\ ___|c | | | | ___|____| | igbt | c/ g |___ | / |e | | | |______/\\/\\/\\_______| | | 2.2k | | | \\ | | e\\ | to points | | | | |______________| | | gndYou should use an ignition coil driver igbt like the hgtp14n40f3vl or the mgp(Iforgettherest). Just go to Digikey and type in mgp, it will come up. If you wanted to use a mosfet you would need a 400 volt rating and a fairly low resistance (like a quarter ohm), and preferably an avalanche rating, which means spendy and the mosfet won't have the clamping protections the coil driver igbt has. So just use a coil driver igbt. You can go with less than 2.2k on the resistors if you use half watt resistors. Now I expect some criticism of this circuit from the pros on the NG, but I've built some and sold them to guys on an antique motorcycle BB over the last few years, no complaints. I use this circuit on my 1973 International Harvester Scout II and my 1952 Harley. With this circuit you can use less resistance in the coil primary circuit -- more zap! For example on the Scout, I don't use a ballast resistor; only the stock coil, which has a little over 1.5 ohms primary resistance. As you can guess, the power transistor needs heat sinking. You will never have to file your points or replace them. You don't need a condenser with the ignition amplifier. (In fact you have to disconnect the condenser.)