Electronics > Projects, Designs, and Technical Stuff
Low quiescent/ standby boost regulator 3.3-500V
Marco:
That Maxim circuit is quite cool ... I completely forgot that type of boost converter existed (seen it called multilevel boost converter as well).
The way series voltage multipliers droop under load (ripple is not the same for every stage) makes it hard to regulate the output voltage using just the voltage on the lowest stage though. A parallel voltage multiplier might be better.
PS. if you really want it small, VMI makes small multiplier modules like PVM302P08 (example of its use in a neutron detector). No idea what it costs though.
Amper:
Yes, im curious too how well this regulation will work, on the other hand the average geiger tubes plateu is also around 100V wide so it may be alright to have 10-20% variation. Measuring the output directly would be possible but also requires very very high resistances not to create to much load. As i said before, 10M will completely overload the converter, 1G seems appropriate but even though 1206 parts in this value exist the board it self would be more conductive... Not even speaking of moisture.
I know about these amazing modules though besides the very high price tag they are also very difficult to find anywhere. My current layout is just about double the board area and requires only pretty common components. Changing the fet to a 300V type i could even raise the voltage to 1.5kV since all the other parts are already capable enough.
Something else i just remembered:
There is also the option to use a string of high voltage zeners in series to the sense reistor dropping the first 400V or so. If the 60M divider just sees the last 100V the current should be small enough and the multiplier is loaded evenly without insane resistors.
SiliconWizard:
I've simulated the "flyback" topology around an LT8494 instead of the LT8330 and I got better results. It would draw ~50mA on average. Still a lot IMO, but it seems hard to do better than this, so if you manage to do better with Maxim's approach, I'll be interested in seeing that. Keep us posted.
The small 1:N coupled inductors from Coilcraft are great, but pretty limited still. They also have miniature flyback transformers that have better specs, except they are only 1:1, so not really usable here. Haven't found much better so far, except with MUCH larger transformers. Or you'd have to have them custom-designed...
I have also tried the approach I had in mind (in simulation only): a conventional boost converter, followed by some oscillator feeding a Cockcroft-Walton multiplier. I was happy to find the LT8415, which has an integrated dual half-bridge, making it ideal for that without the need of any external transistors or additional integrated high-voltage half/full-bridge. Unfortunately, the max switching current of the LT8415 is so low (25mA) that the output of the multiplier can never reach 500V, not even close... Could be doable for a lower output voltage though such as 100V to 200V...
Marco:
Oh, there's already a complete open source design using the Maxim technique specifically for Geiger tubes.
They also use avalanche diodes for feedback BTW.
EmmanuelFaure:
There's an easier method : Boost converter with an tapped inductor/autotransformer in place of the inductor. Flyback have an unecessary component count, transformers are not cheap, and you don't need the isolation between input and output.
Schematic for example here, on page 43 :
https://www.analog.com/media/en/technical-documentation/application-notes/an19fc.pdf
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