![]() ![]() ![]() I'll follow up with more info when it's wrung out. This keeps Q1, the coil, and batteries from being killed.Īgain, I haven't built the circuit yet. It'll turn the coil off after about 0.3 seconds if the hall is stuck low (or shorted to ground), or the points don't open. C2 prevents the coil from being turned on too long. The coil fires when the sensor output goes high (or the points open). The coil charges when the Hall sensor output goes low (or breaker points close). R3, R4, D4, and R2 are the input circuit. JP1 is a jumper that can be removed to save power if the LED isn't being used. Q2 is a small Darlington used to provide enough base current to Q1.ĭ3 is the timing indicator. If the two zener diodes conduct, it will actually turn on the transistor by feedback enough to keep voltages within limits. Being connected between the collector and base rather than collector to ground protects the transistor's collector to base junction as well. Allowing the coil voltage to get too high can damage the itsy bitsy coils we use. The second function, believe it or not, is preventing the coil output voltage from getting too high (how high it will get is dependant on your coil) if the spark plug is disconnected. The obvious one is to clamp the voltage across the transistor to less than 400V. It serves as the coil driver.ĭ1 and D2 have a few functions. Q1 is a 400V Darlington power transistor with internal flyback diode. I haven't yet built this, but I have run a PSPICE simulation and it works.ġ) No heatsink required for the driver transistor to keep the unit small.Ģ) Very low current draw with the motor not running and when the coil is off.ĥ) Turn off coil current if the engine is stopped with the hall effect sensor triggered.Ħ) Prevention of internal arcing in the coil if no spark plug is connected.ħ) Usable with breaker points instead of Hall effect sensors.Ĩ) 4.5 to 14V operation. So, as an Electronics Engineer by trade, I designed my own. They usually had one or more of the following faults:ģ) Would overheat the driver transistor and/or the coil if the engine was not running with the crank in a position where the ignition was triggered.Ĥ) Consumed power to keep the coil turned off. I searched around for suitable circuits, but found virtually all unacceptable. See post #11.įor my Farm Boy build, I wanted to wind my own ignition coil and build my own ignition circuit. EDIT: This circuit has been revised and improved. ![]()
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