[sdiy] OT- Battery powered HV supply?

[mirwin at qouest.net]

Toby,
Very good low power HV supply can be made using a CMOS 555 timer with a 
PNP transistor  switch, use one of the tiny HV transformers from a 
disposible camera with built-in photoflash (also contains a HV 
rectifier). Set it up so the timer produces very brief (low duty cycle) 
negative-going spikes  at around 100 Hz rate. Timer output connected to 
PNP base through 100-220 ohm resistor, PNP emitter connects to V(+), 
transformer primary connected between ground and PNP collector. Run 
on 2.5 to 3 volts (two NiCd or two "AA"). Use lots of bypassing and a 5 
volt Zener across the supply to suppress spikes  (to protect CMOS 
timer). Easy to get 500 to 1000V this way. Be careful not to exceed 
transformer ratings. Current consumption  increases as duty cycle 
increases, battery drain lower limit is around 400 microamps at 3V  (the 
timer chip alone takes around 150 uA). Most/all dedicated switching 
power supply chips take more current than this just to run the chip. 
An alternative is the one-transistor "ringing choke converter", simpler 
to build, but more difficult to get working (eg. wind your own 
inductor). The HV supplies from battery-operated fluorescent lights are 
optimized for lots of power output (and have large battery drain).
Cheers, Mike