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I want to design a power supply for 8 IN-14 nixie tubes. The tubes are controlled by a raspberry pi which needs a 5V supply voltage. I found this nixie power supply kit which converts 9V to about 180V. So my current setup consists of a 9V AC adapter, an L78S05C linear regulator, and the nixie supply kit. With my advanced temperature sensing method (using my finger), I have found that the L78S05C is getting really hot and other parts of the supply (MOSFET and Inductor) get moderately hot. I am not sure if the temperature of the nixie supply is a problem or not.

I think the linear regulator should be replaced by a buck converter. Is this the right way to go about it? Or should I try to start from 5V and convert that to the required 180V? And how would I go about that? A flyback converter or two boost converters in series?

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    \$\begingroup\$ It is much easier to go from 9V to 180V than to go from 5V to 180V. So I'd keep the 9V source. So this really isn't about a high voltage supply. It's a question about using a buck for your 5 V, I think. \$\endgroup\$ – jonk Oct 6 '17 at 7:26
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    \$\begingroup\$ Simpler : heatsink the 7805 if you haven't already. \$\endgroup\$ – Brian Drummond Oct 6 '17 at 10:59
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With your current setup, using a buck converter to replace the L78S05C will solve your efficiency (i.e. heat problem). There are lots of choices to choose from at TI and others.

The lower profile, less parts count solution would be to use the 5v source to power both the raspberry pie and the Nixie Tube power supply. There are some 5v Nixie tube power supplies on Ebay (just search nixie tube power supply). If you are interested, I'm designing a low profile nixie supply that can be powered from 5v and will output 170v (i.e. or 160v as pointed out above for longer lifetime). The blog is at www.surfncircuits.com and all the schematic, layout, and bom files are at github. The disclaimer is that the design is finished, but the experimental verification needs to be completed. I hope to finish it shortly, but the parts are arriving this week.

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It sounds like the problem is with the 5V supply, and the Nixie supply is OK. You don't say which model Raspberry Pi you are using, but the Model B takes around 350mA when idle and up to 500mA when working hard (and it can take MUCH more if you have the USB outlets loaded). Thus you have a minimum dissipation of 1.2W for the L78S05C, so this is not efficient. A simple buck switcher should fix this problem. I would keep the direct 9V - 180V conversion, as you cannot gain anything by having two converters in series.

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I'd use a 5V adapter to power the Raspberry Pi. The Nixie supply would probably work with 5V input, it will be less efficient, but should work. And don't fry Nixies with 180V. 160V is usually sufficient and this extends their life considerably.

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