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Variations on Nixie Power Supply Design

Since I started tinkering with Nixie and other Neon tubes, I found the need for simple (read: inexpensive) high voltage power supply capable of generating over 170V from 5V DC.

After a bit of research I found that most of the high voltage power supply designs use boost converter driven by a PWM controller IC such as MC34063, with a high voltage MOSFET switching an inductor. (Here’s an example of the design.)
Those designs looked a bit overkill to me, so I started designing my own from scratch.

Since I’m familiar with transistor based blocking oscillator circuit to boost voltage (i.e. Joule Thief), I wanted to see if I can use a similar circuit. The switching transistor has to withstand the output voltage of 180V so I picked some high voltage transistors and experimented. Turned out that typical high voltage transistors (C-E breakdown of more than 200V) were too wimpy for the purpose, and the simple two transistor circuit that I was using was not capable of very high duty cycle demanded by high input/output voltage ratio (over 90%).

One way to reduce requirement for the boost converter is to add voltage multiplier at the output. I added a 3 stageĀ voltage multiplier to a circuit using pretty ordinary (inexpensive) transistors. This circuit was able to provide required voltage (about 170V) and up to around 3 to 4mA of driving current to medium sized Nixie like IN-12.

After building a couple of prototype Nixie clocks using this circuit, I found a very nice transistor capable of handling 100V and 1A current.

With this new transistor, I can now reduce the voltage multiplier stage to only one, since the boost circuit itself can produce up to 100V (ok, with safety margin, more like 90V). This circuit outperformed the prior version, producing about 8mA at 170V.

Super simple HVPS using only two transistors. 180V output capable.

Simple two transistor HVPS on a Nixie clock controller PCBA. (Inside yellow rectangle – fits in 12mm x 32mm)

While I was happy with this design – especially the size and cost – and built a couple of Nixie clocks and IN-13 Neon indicator tube projects with it, I still wanted to make it better (mostly wanted more power).

If I can find a transistor capable of withstanding over 200V with a reasonably low loss, I can forgo the voltage multiplier. However the only options that I can find were MOSFETs.

After checking the prices of high voltage MOSFETs such as IRF740, I concluded that it can be more cost effective if I can make it work, since I’ll be removing two diodes and capacitors from the voltage multiplier.

After a bit of experimentation, I got it to work! Here’s the MOSFET based circuit. Note that this design needs at least 9V of input voltage to work (due to the MOSFETs gate voltage). So for the 5V powered projects, I’d still use BJT based design.

Super simple HVPS using only two transistors. 240V output capable with 12V input.

This MOSFET based design is capable of delivering at least 50mA at 200V.

7 Responses

  1. David Brenner

    Very good schematic.
    Thank you.

    I am trying to switch a schematic to use MOSFETs instead of bipolar transistors.
    This is the schematic (made in Proteus 8):
    It has 2 versions (one for 16 mA output and one for 32 mA).
    The input voltage can vary from 4..5 to 8.4V (default is 7.2V).
    I used pnps because I couldn’t find the spice model for the STN851 (found only for STN951).
    But in the final version it will have npns and/or n-channels.
    My question is: is it worth switching to MOSFETs in this schematic?
    If yes, can you please give me a few ideas/tips?

    Thank you again.

    Best regards,

    December 12, 2018 at 10:24 am

    • Hello David,

      I can’t open the schematics you posted. Can you provide PDF or image files?

      December 12, 2018 at 11:04 am

      • David Brenner

        Thank you.

        For opening the file you need Proteus 8.
        Here is a screen capture of the test schematic:

        I will try to explain it a bit:
        Bat2 + L2 + C6 are used as a few ms timer.
        Rl1 simulates the real switch.
        Bat1 is a 6 cell 1300mAh Ni-Mh battery.
        R4 is the internal resistance of Bat1.
        I use C5 because at startup the oscillator requires more power than usual.
        R5 is the internal resistance of L1.
        I use C7, C8, R9, R10 just in this schematic to collect data.
        R8 discharges C2 at poweroff (without it the driver won’t start next time).
        D2..D7 simulates a 6 x 6 2.7 V led matrice.

        December 14, 2018 at 12:40 am

  2. Johan Carlsson

    Nice work! Could you upload the schematic for the ZTX653 version of the circuit? I’m curious to see what component values you dialed in.

    October 9, 2018 at 1:14 am

    • ZTX653 version is pretty much the same as NSS1C201L circuit posted. I use them interchangeably depending on the package (SMD or through-hole).

      October 9, 2018 at 12:48 pm

      • Johan Carlsson

        I’ve tried something similar with the MPSA42 instead of the ZTX653, but didn’t get my circuit to work. Are you familiar with the MPSA42? I might try to use it in your circuit while I wait for my ZTX653 order to arrive.

        October 9, 2018 at 1:52 pm

        • I did try MPSA42 and many transistors alike. High (ish) voltage, small size BJT’s don’t do the job. I found KSP/MPSA06, which is only 80V, to work ok for low power situations. ZTX653 works remarkably well and has 100V Vce rating to help matters a bit.

          October 9, 2018 at 2:05 pm

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