Hv Power supply


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Project: Hv Power-supply
Name Hv Power-supply
Initiator Duality
Status .1%
Skills Electronics
Summary A power-supply for powering e.g. vacuum-tubes or indicator lights, or nixies.


I bought some nice indicator tubes em84 and em85 and these are the reason for starting this project, in the past I did some projects with Radio tubes, and other vacuum-tubes but never had a real way of running them without a big bulky transformer.

With this power-supply I hope to make the em84 and em85 tubes work and learn how to make these kinds of power-supplies.


The goal is building a power-supply that is nice and handy, for vacuum-tube experiments and the like. It'll be relatively small and portable, and easy to scale up. since the High voltage generation part can be changed to something that has more power and can deliver a faster charge rate.


The plan is to make a power supply that doesn't go over a certain target voltage, but also stays at the target voltage.


What it should do:

  • max voltage: 350V
  • max wattage: 5W
  • stable at target voltage.

what the hardware looks like.

I put a few pieces together thinking about this, It basically consists out of two parts.

  • High-voltage Generator.
  • sense / feedback.

For sensing the voltage on the output, I thought to use a comparator, I know that with a comparator you can sense a voltage at the terminals and act upon it. so I was digging around on the Internet and found exactly what I was planning on doing but someone already done it (mostly) LowRippleHVsupply. only on the link it goes from 0 > 1200~ I'll have to recalculate some values there.

For the High-voltage part I won't be building the actual circuit that generates the high-voltage that will be done by a board that I pulled out of a old camcorder. it came from the eye piece that contained a little miniature cathode ray tube. This Generator, (which is essentially a mini flyback with flyback driver onboard) will be charging a capacitor.

The Idea here is that the High-voltage generator charges a capacitor to a sufficient voltage to run the project, while the comparator senses (via a voltage-divider) what the actuall voltage is on the capacitor, When it reaches the desired target Voltage it switches the High voltage generator off, and when the levels drop low enough it turns the generator back on. In this way the comparator will ensure that the generator does not over charge the capacitor, and that the voltage level on the capacitor stays at the target voltage. I thought about using a fixed voltage divider on the non inverting input, but that way the power-supply output voltage, would be fixed, so I decided to put a potentiometer on the inverting input of the comparator.

  • this would allow setting the desired output voltage
  • give fine control over the output voltage.


The basic steps I'll undertake for this project are:

  • build a circuit that can switch a device on and off (transistor + led at first)
  • build a comparator circuit to control said transistor, when a smaller (say 10V) is reached on a Capacitor (charged by bench power-supply.
  • charge capacitor to say 30V with the high-voltage generator.

the first stage will test if the switching works (for turning the high voltage power supply on and off). the seconds stage will test whether the comparator logic works. the third stage will test whether the comparator logic works and correctly senses the target voltage with the high-voltage generator connected.