need help with ignition coil driver

[viper77707]

will an ne555p work instead of just a regular ne555?i have tried a ka555 with this circuit and it worked but all of these ne555p's i can get it to work!here is the circuit:
http://www.geocities.com/capecanaveral/lab/5322/coildrv.htm
and am i supposed to connect the middle pin and one of the other pins on the potentiometer?

 

[jpanhalt]

See page 4 of this datasheet: https://pdf1.alldatasheet.com/datasheet-pdf/view/161277/TI/NE555P.html

The P just means it is a different package, which is explained on the datasheet.

The schematic indicates that the center pin should be attached to one of the other two pins of the pot.

John

 

[k7elp60]

I would add two componets to the circuit. A silicon diode like a 1N5400 in parallel with the ignition coil, the cathode connected to +12V and the anode connected to the collector side of the 2N3055. I would add a 10 uF electrolytic capacitor between pin 8 and pin 1 of the 555. + to pin 8 and negative to pin 1

 

[viper77707]

well crap....i just cant get the circuit to oscillate then....thanks alot though

 

[Roff]

I would add two componets to the circuit. A silicon diode like a 1N5400 in parallel with the ignition coil, the cathode connected to +12V and the anode connected to the collector side of the 2N3055. I would add a 10 uF electrolytic capacitor between pin 8 and pin 1 of the 555. + to pin 8 and negative to pin 1

Maybe put a series RC snubber across the coil, but I think a diode defeats the purpose. (I believe) Transistor-based ignition coil drivers generate the high voltage on turn-off. Remember that the transistor is switching the "primary" of an autotransformer. It charges up the field while it is on, and the high voltage is generated when the field collapses.

 

[k7elp60]

Maybe put a series RC snubber across the coil, but I think a diode defeats the purpose. (I believe) Transistor-based ignition coil drivers generate the high voltage on turn-off. Remember that the transistor is switching the "primary" of an autotransformer. It charges up the field while it is on, and the high voltage is generated when the field collapses.

There I go having a brain fart again. Thanks Roff for getting me back on track.

 

[Hero999]

Maybe put a series RC snubber across the coil, but I think a diode defeats the purpose. (I believe) Transistor-based ignition coil drivers generate the high voltage on turn-off. Remember that the transistor is switching the "primary" of an autotransformer. It charges up the field while it is on, and the high voltage is generated when the field collapses.

I just make sure I use a transistor with a high enough voltage rating (depends on the coil's Q at the resonant frequency with parasitic capacitance) or that it's avalanche rated to the amount of energy stored in the coil.

Aslo you don't actually need a resistor in the snubber circuit, if you know the coil's inductance and the peak current, then you can work our the maximum voltage you'd expect across the capacitor, the larger the capacitor the lower the voltage. Yes, the resonant circuit will ring a bit but the energy isn't being wasted and proving the resonant frequency is significantly higher than the switching frequency then it won't matter.