3-Knob Tube Driver Build.

[DrNomis_44]

How do voltage multiplier circuits work? I’ve come across them before but I just don’t get how you can get something like 90v Dom a 15v supply...

It's pretty simple really, when the output of the 60kHz oscillator goes high, each of the 1N4007 diodes will conduct and charge up each of the 47uF/100V caps, since there are five of the 47uF/100V caps, each of them will charge up to about a fifth of the output voltage, when the output of the 60kHz oscillator goes low, each of the 1N4007 diodes will stop conducting, the cap on the end of the 10k resistor will then charge up to the sum of the charges on all the other 47uF/100V caps, this happens at the rate of the 60kHz oscillator.

With five 47uF/100V caps, the output voltage will be about +45V DC, to get +90V DC out of the circuit you just add another five 47uF/100V caps and 1N4007 diodes, I've actually tried doing it in practice and it does work.

Marcel could probably elaborate more on how the circuit works.