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HV buck vreg

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Oznog

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I have a problem where I'd need to get 5v at just a few mA out of a hv supply. It might be as low as 96v and perhaps as high as 200v, maybe even 300v for some applications.

Now a zener can do it, but not very efficiently. This is a battery bank and it would take 1W out of a 200v battery to provide 5mA. So I'd like a buck switching reg.

This looks a bit tricky though. I didn't see any regs which like 200v for a source voltage! Unless I'm missing one somewhere. Actually, I have need to do this as both +5v from battery ground (positive regulator) and also as the battery + voltage minus 5v (negative regulator). The need for a negative reg seems to lower my options somewhat.

One thought was that the buck could power itself with the 5v it generates. Or if necessary maybe it could generate 12v, power itself off that, and then a second reg makes 5v for the load. That brings up a question of how it gets started, and the zener may be the solution there. After it is generating output it can switch off the zener.

Does this sound practical? I'm effectively asking for zero dropout here- the switcher reg supply voltage will be the same as its output voltage- can a switcher DO this?
 
The standard LM317 can be operated at pretty high voltages as long as the input to output differential is OK. The data book shows a 1.2 to 160V @25mA supply from over 170V input. You will have the drop of the regulator, but it is an off the shelf design.
 
You your using such an PSU right now wen reeding this website.

Its an PC PSU.They work from a wide range of voltages.Some work from 100V mains to 240V mains whithout needing to flip an a switch to tell it on what voltage it is.

here you will get about 20A out the 5V rail.
 
HV supply

Can't this be implemented using a transformer say 9-0-9v and then regulating it to the required 5v using a 7805? Or am I misunderstanding something here? :D
 
He didnt metchon if its AC or DC.

An switchmode aculy coverts mains to DC ferore it drives it in its ferite transformers so an switchmode dosent care if its geting AC or DC(Since the didodes and caps make it DC if its AC or DC)
 
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