Nixie HV switching PSU

MAX 1771 V4 populated top 1

From the comments on our earlier HV Nixie DC-DC switching power supply post, here’s a Nixie HV switching PSU by Nick De Smith:

It is probably beyond the scope of this simple document to describe the operation of switch-mode power supplies (SMPSs) – suffice to say the technique relies on the voltage pulse you get from rapidly collapsing the magnetic field in an inductor. This is done many thousands of times a second and the output pulses are collected and smoothed. Whilst this sounds simple, in practice it is complex to do well – there are a number of key design decisions that have to be made, and board layout is critical – SMPSs will not work well when built on Vero/StripBoard or prototyping plug-in boards – in fact, they may not work at all!
So, if SMPSs are tricky to work with, why use them? Simple – when they work they are brilliant! They are very small, cheap, completely solid-state, run cool and can be 90% or more efficient. This last point, efficiency, can be very important. SMPSs can lower a voltage (a “buck” converter) or increase the input voltage (a “boost” converter).

Via the comments. Thanks Xevel!

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  1. I think I’m going to catch some flak for saying this, but: I wish hobbyists would stop using tantalum caps. When was the last time we saw a tantalum cap in a iFixit teardown? MLCs and cans work fine.

  2. HI – I’m the author of that article.

    Firstly, I’m not an amateur, which is why I probably use tantalum caps – you are free, of course, to use any other low-ESR cap you like, but for its size, that was the cap I chose – It’s also readily available (or was, last time I checked).

    There is absolutely no problem with clearance – I used the UL 60950-1 2nd Edition Tables 2K, 2L, 2M or 2N as the rules for this PCB – the maximum voltage is 250VDC equating to 40 volts/mil or about 1.6 kV/mm – remember I use a solder mask and could also add a conformal layer should the PSU be use in a condensing environment.



  3. Thank you for responding to my comment. I see that AVX TPS is suggested in the SMD column in the MAX1771 data sheet (dated 2002!). The through-hole suggestions in the same table are electrolyte caps. A low-ESR cap may have a size penalty compared to a tantalum, but with a 300kHz PWM, power parts sized for 2A isn’t going to be too small anyhow. At least then I would not have do all the tantalum derating checks… particularly when using them for large surge currents.

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