How to build a ignition coil driver driver#

Please tell me if I have something terribly wrong. There will be resistors in there (of course), but that's just my general concept. I studied some CDI schematics and decided I needed to hop the voltage up with a transformer and discharge it through a capacitor like CDI does. If you clamp the primary with a diode, it will also affect the output of the ignition coil. Ignition systems have circuitry to deal with the kick back so it causes no harm yet allows the coil to do its job effectively. The 'ring back', or inductive kick is useful in an ignition circuit. Yes, the clamping diode does short out the reverse charge, This is primarily to protect the rest of the circuitry connected to the same system. I don't see how this would prevent a build up of the magnetic field or prevent it's collapsing. My thinking is I would just short out any reverse charge with a diode across the primary. My understanding is that if you stop the current going into the coil (done by the transistor switching) then the magnetic field collapses inducing a voltage in the secondary, but continues through the core and induces a reverse polarity 'ringing' back into the primary. Does that make sense? Let us know how your experimentation proceeds! If you 'quench' the feedback, you're also allowing the current to decay slowly (related to the L/R time constant of the primary winding), instead of forcing the current to shut off quickly (but, as you point out, in a way that can be ugly / noisy / spiky). You need a rapid change in primary coil current in order to generate a large voltage in the secondary winding of the transformer, and there's going to be an inductive part of that in the primary. I figure one of those reverse polarity across the coil should quench most feedback.Ī reverse polarity diode across the coil may be good for protecting the rest of your circuit, but it might severly degrade your ability to generate a spark.

Didn't have any zener diodes or MOV's, so I got a couple rectifier diodes rated for 400v. I picked up a pair of 2n3055 transistors at radio shack. I'll probably get to it this weekend, maybe radio shack will have what I need and I won't need to wait. I will be adding more features later, but for now this is the important one. The discussion you referenced has a link to this The first schematic looks like about what I am thinking, but with a MOV in place of RC1 and maybe a diode or two between the transistor and the coil.

How to build a ignition coil driver driver#

The coil driver circuit needs to supply 12 volts to the ignition coil (from the motor cycle battery) until the calculated time of spark, in which it needs to brake the circuit quickly and precisely while isolating the sensitive micro-controller from any high voltage feedback coming out of the coil. I will use input from the pulse coil and alternator to estimate engine speed and position then dynamically determine spark timing in software. I am intending to replace the CDI (Capacitor Discharge Ignition) system with a programmable micro-controller. I doubt that three of the 2N7000's in parallel would have enough current-handling capacity to produce a good spark.ĬDI = Capacitor Discharge Ignition - is that correct for your motorcycle? Are you trying to fix the CDI system, or to replace it with an inductive-type spark generator? It sounds like the latter, but I just wanted to check. I also no longer have the details of that project, but there was some discussion here. Should be some interesting programming once I get the circuitry figured out. I have spares of everything, but I don't need coil feedback killing stuff.

I am going to be building a replacement for the CDI module on my old motor cycle (parts no longer available), and I am wondering if 3 parallel mosfets from the kit should be able to safely drive a 12v ignition coil, and what sort of circuit protection would be best. I have not even opened my kit yet (it came today) but I would like to get started on the coil driver circuit design so I can order parts if I need to.