Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!unmvax!ariel.unm.edu!hydra.unm.edu!ee5391aa From: ee5391aa@hydra.unm.edu (Duke McMullan n5gax) Newsgroups: sci.electronics Subject: Re: How to make 600VDC from 800VDC Message-ID: <1990Oct18.021112.8416@ariel.unm.edu> Date: 18 Oct 90 02:11:12 GMT References: <92@decabo.enet.dec.com> Sender: news@ariel.unm.edu (USENET News System) Organization: University of New Mexico, Albuquerque Lines: 44 In article <92@decabo.enet.dec.com> (J. Brewer) writes: > I have a need to obtain 600VDC at about 150-200mA from an > 800VDC supply. It need not be exceptionally well regulated > voltage-wise, but does anyone have a simple solution? > (not as simple as a resistive voltage divider however!) Whew...that's a fairly high voltage. If the 800V is pretty stable, you could use a voltage divider to give you a reference voltage of about 600V, then feed that into a source follower (or emitter follower) if you can find a transistor that'll handle the V & I you're wanting. You _might_ even dig up an old triode (gasp!) that'll handle the current, and set it up in cathode follower configuration...those three circuits are basically the same thing... voltage followers. Very high input impedance, very low output impedance, with the output voltage following (more or less) the input voltage. One base-emit- ter drop wouldn't be worth worrying about at those potentials. A switching regulator would be more efficient, but it may be more complex than you want...it rapidly gets to the point where it's easier just to build a 600VDC supply from scratch.... Another thought occurs to me, but I don't think it would handle the current: You could stick several gas-discharge voltage-regulator tubes in series with the supply to get the drop you want...IF you can still find those VR tubes (type OA2, etc., if memory serves) and IF they'll handle the current. A modern equivalent would be a 200V zener diode. I'm sure you could find such a critter, but 200V * 0.2A is about 40 watts...and the diode has to safely dissipate all that. If you can find such a diode, that's probably the simplest method. Think "heat-sink". Heh. You _could_ come up with a 200VDC supply, and put it in series with the 800V supply, polarity opposed. It would _work_...but it's kinda like swatting a mosquito with an ax.... Lastly, perhaps a DC transformer...? ;^) d -- "It's my _dessert_ that's gross! Look, a thermos full of phlegm!" -- Calvin Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.edu