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I am looking to build a power supply for a NIXIE tube. They need to output 180v at 4ma but will run off of a 3v lithium battery. The battery can take the current requirements for the input, but at the moment I am struggling to make a single 3v to 180v boost converter. I wondered if you can have one that boosts the voltage to say 30v and then a second that takes it up to 180v.

As well as that I don't want to use an off the shelf converter chip, I want the PWM to be created by a microcontroller (probably a PIC). Is this possible? and is it the best way around the problem?

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  • \$\begingroup\$ Build a flyback. \$\endgroup\$
    – John D
    Mar 17, 2018 at 20:35
  • \$\begingroup\$ Of course you can cascade converters. When calculating the input power requirement, don't forget to consider that each regulator will operate at less than 100% efficiency. My guess is that you will have around 50-60% overall efficiency with a two-stage design. \$\endgroup\$
    – user57037
    Mar 17, 2018 at 20:35
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    \$\begingroup\$ Yes you can, but it doesn't make much sense. In this cases you just use power supplies that use transformers to increase voltage without so much penalty as you would have with boost converter with very high duty cycles. Usually for a boost you don't go with factors higher than 6. For this case, considering also it's low power a flyback would be a nice option. Check this link dos4ever.com/flyback/flyback.html#flyback2 \$\endgroup\$
    – Andrés
    Mar 17, 2018 at 20:45
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    \$\begingroup\$ Sure thing! Adding to John D’s comment. Boost is “limited” to a factor of five per step so if you cascade two, you can boost by a factor of 25. If you haven’t designed a switching converter before, I would recommend you to go for cascaded boost converters since flyback is the minimum part count converter, but it’s very challenging for a beginner to design the transformer needed. \$\endgroup\$
    – winny
    Mar 17, 2018 at 20:48
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    \$\begingroup\$ Sorry, I didn't have time to add any more when I made my first comment, but the comments by everyone else are valid. The "best" way to do this is with a flyback, but as a beginner I would NOT recommend trying to do a digitally controlled flyback or even a boost when there are controllers available that will be much easier to use. If you insist on digital control hopefully you have a good grasp of control theory, sampled data systems, the right-half-plane zero in boost topologies, and good power electronics layout and component selection practices. \$\endgroup\$
    – John D
    Mar 17, 2018 at 21:51

2 Answers 2

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A single stage boost converter from 3v to 180v would be very challenging, too large a ratio for the compromise design of the boost inductor.

However, a single stage flyback would be straightforward.

An alternative two stage design that is very robust, would be an initial push-pull inverter to an intermediate AC voltage, followed by a Cockcroft Walton multiplier.

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Why not simply take that 3v and make it a square wave with an H-bridge or push-pull and feed that into a 60:1 ferrite-cored transformer and then full-wave rectify the output of that? With power that low (<1W) 20kHz switching freq should be plenty fast enough and the core would still be quite small. That seems far more straightforward than cascading boost converters with pic controllers.

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