I just found a bunch of gas discharge displays in my scrap parts bin (see
UK mains voltage is 325V peak to peak (give or take 15V), half of which happens to give around 162.5V which would be enough to run these displays.
Switch-mode power supplies generally seem to feed mains in through a fuse, isolating transformer, and then into a bridge rectifier and smoothing caps.
I have a spare one which would be ideal for supplying power to the ICs which can drive these displays, and I'm wondering if I can also use it to supply the high voltage DC needed.
a) is there a cunning way of just getting the 155-170V DC that I need? I was thinking of sticking the PSU's bridge rectifier output through a potential divider circuit to generate the voltage I need (these displays are pretty low current). Would a half-wave recifier added in past the isolating transformer on the PSU and a large smoothing capacitor be a better bet though? (my worry there is that on a 'low' mains supply of 220V the 155V DC might not be enough to run the displays)
b) Say I go for the potential divider approach running off the PSU's existing bridge rectifier. I'd want a common ground between the rectifier output and the power supply's normal GND output so that I could use the display driver IC's that I have to drive the displays directly. There's no continuity between the bridge -ve output in the PSU and the eventual PSU's GND though, so I can't help feeling that coupling these directly together is asking for trouble!! :-)
Do I need to use a completely seperate isolating transformer, bridge, smoothing cap, potential divider etc. running off the mains in parallel with this switchmode, and *then* couple the grounds together?
cheers
Jules