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I want to make an AC HV powwer supply. I´ve seen in several sites that an ingnition coil gives you AC. I plan to use a 555 circuit to drive the coil. However, I think that if we are using a train of pulses to excite the primary of the coil, the output should be pulsed DC, not AC, is that correct?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
What exactly does "pulsed DC" mean?
The terms AC and DC were invented to distinguish different kinds of mains power. For general waveforms, usually DC means the value averaged over time, and AC means the time-varying component.
On the secondary of an ignition coil, or any other transformer, the average voltage is necessarily zero (no DC). DC current is allowed, and in practice that would go along with a small DC voltage (the I*R drop in the winding resistance).
I never heard of an ignition coil used as a conventional transformer, with pure AC input and output. Would expect it to work fine in some frequency band. You could try driving one with a 555 and a series capacitor to block DC & make coil resonances more interesting.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
When I used my HV probe, I got a huge pulse with a lot of sine garbage on it. Iggies have a single "I" core for the can type. And the HEI/TFI types have a "EE" core with a big gap. Theres no reason you cant put a positive pulse into the primary, then a negative one after some dead time.
Iggies are real hard on noise and don't preserve waveform. so remember that.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
An iggy coil works fine for a transformer, especially if you drive it at resonance. I did some experiments waaaay back with a sig-gen and an audio amplifier. IIRC, the output Q'ed up about tenfold above the turns ratio around 8kHz. That may or may not be useful for you depending on how you track the resonance, and how the coil loading changes with sparks or rectifier parasitics. I would imagine that the same drive control as for a DRSSTC would work OK.
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Output from an ingnition coil. AC or DC?
You could try driving one with a 555 and a series capacitor to block DC & make coil resonances more interesting.
