Ignition coil driver

coil.jpg (37448 bytes)The 555-timer chip based ignition coil driver is good, and the components are easy to find. The circuit is approximately the one given in the 555 timer data sheets, www.national.com search for NE555. The output pin 3 drives the base of a 2n3055 transistor, or, the gate of a MOSFET (for higher frequencies) like IRF840.
A very simple design can be found at http://www.Geocities.com/CapeCanaveral/Lab/5322/coildrv.htm which is easy to build. My driver is based on that one.

One ignition coil terminal goes to +12V, the other to the collector or drain of the transistor. The emitter or source of the transistor goes to ground (i.e. 12V battery negative terminal). This ground is also connected to the 555 timer ground and 9V battery negative terminal. A 10nF capacitor rated 1kV accross the transistor collector and emitter, plus a parallel diode pointing "up" from ground, and a 60V varistor (MOV or VDR) accross the ignition coil terminals (i.e. +12V and the collector of the transistor) are useful to protect the transistor from voltage spikes that might kill it.

Some possible projects for coil usage: arcs and sparks, plasma globes filled with helium and other inert gases for daylight visible plasma, vacuum plasma globes i.e. ordinary larger lightbulbs for plasma (best seen in the dark), light small and maybe even large fluorescent light tubes, build a miniature Jacobs ladder using a lower hv ignition coil (<40kV) with larger output current (1 or 2mA, or more), make a hugely exaggerated bug and fly zapper, assemble a Tesla coil primary stage power supply for charging the capacitor, and more. Some less legal uses: a spark gap radio transmitter, and/or distant MW radio signal blocking locally.

Here some pics of the board.

pulser_tv.jpg (9199 bytes)Top view. Amazingly, the small heatsink really is enough for not so long, casual operation. Limiting the input current to 9A peaks max doesn't seem to have any performance losses in ignition coil output. This thing runs off a small 12V lead gel battery.
Right corner is 9V battery for the 555 timer, left bottom corner is DIP switch and capacitor bank for timing capacitor selection, left panel has two 47k pots for frequency and duty cycle adjustment.

pulser_bv.jpg (41530 bytes)Bottom view. Maybe not so nice soldering and no proff photo etching, and a bit dirty board as well, but at least it works. The diode from 12V GND to 9V GND in the pic was added after a few tries. The 12V power supply connects to the top right connectors (yel, gn), and the ignition coil to the bottom right ones (gn, wht). The piezo buzzer is connected to pin 3 of the 555 timer, with a 100k series resistor to ground. It makes the frequency audible so adjustment is easier.