J
Jules
Guest
I just found a bunch of gas discharge displays in my scrap parts bin (see
http://www.datamath.org/Display/SP352.htm for the same type) and
coincidentally need a few 7-segment displays for a project. Using these
would look pretty cool.
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
http://www.datamath.org/Display/SP352.htm for the same type) and
coincidentally need a few 7-segment displays for a project. Using these
would look pretty cool.
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