Don’t put your hand in this one! This uses a disposable camera photoflash running off 3 V using a BD140 and heatsink substituted for the main HV transistor so it can now run at 1.5 A.
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Here is a similar photoflash circuit diagram. I have added a .01 uF capacitor across the ‘charge’ switch which is short-circuited when ON switch is off which keeps it running continuously. I have replaced the main capacitor (120uF 330V) with a 2.25 uF polyester (2 x 5.5 in series) with a 30 K charging resistor. There is a single SIDAC 230 V which discharges this into the 14 turn primary wound onto a TV flyback transformer. Not fancy, not neat but no cost. Candy box HV. No Liquorice Allsorts.
The disposable photoflash unit with the electronics removed shown charged by the 1.5 V battery.
The completed candy box HV which produces a 1.5 inch spark with a repetition rate of about 2 Hz. It is “safe” to touch giving a mild pinprick sensation. This formed one part of my display at a University Expo recently where I was offering “free” electric shocks. I would demonstrate on my arm first before calling for volunteers and it was quite a popular display.
This is the waveform of the output at 20 uS per division, which is a damped wave of around 25 kHz with a superimposed signal of about 1 MHz on top. It is about 40 kV at 20 uA but measurements are difficult at this frequency.
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Photo Date: 2005