(J. Brewer) (10/17/90)
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!) Pointers to databook circuits or devices greatly appreciated. Thank you
ee5391aa@hydra.unm.edu (Duke McMullan n5gax) (10/18/90)
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
jws@thumper.mlb.semi.harris.com (James W. Swonger) (10/18/90)
800V+ --------------|------| | | > | Limiting resistor ~ < | 10K ohms (20mA base > | drive, assume Hfe is | | / >= 10. | |/ TV flyback (horizontal +----| output) 1500V BVceo | |\ at least 50W. Better to --- | V parallel a couple with ^ | emitter ballast resistors. /_\ |____________ 600V+ | . . Stack of diodes with . breakdown ~ 600V | --- ^ /_\ | __|__ /////
davet@tsdiag.ccur.com (Dave Tiller N2KAU) (10/18/90)
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!)
-
- Pointers to databook circuits or devices greatly appreciated.
-
- Thank you
How about:
/ /
------800V------>|------>|--------/\/\/-----600v----<load>----
/ / R |
100V zener 100V (I limit) <GND>
You may be able to find one 200V zener, I'm not sure, though. Choose
zeners of sufficient current capability for your application.
--
David E. Tiller davet@tsdiag.ccur.com | Concurrent Computer Corp.
FAX: 201-870-5952 Ph: (201) 870-4119 (w) | 2 Crescent Place, M/S 117
UUCP: ucbvax!rutgers!petsd!tsdiag!davet | Oceanport NJ, 07757
ICBM: 40 16' 52" N 73 59' 00" W | N2KAU @ NN2Z
dfs@doe.carleton.ca (David F. Skoll) (10/18/90)
In <1112@tsdiag.ccur.com> davet@tsdiag.ccur.com (Dave Tiller N2KAU) writes: >How about: > / / >------800V------>|------>|--------/\/\/-----600v----<load>---- > / / R | > 100V zener 100V (I limit) <GND> Ouch! First of all, the Zeners should be facing the other way - we're interested in reverse breakdown voltage here. The above circuit will give you a very nice 798V or so supply Secondly, with the zeners in series with the load, one-quarter of the total power dissipation takes place in the diodes which is rather nasty. (Same current as load through diodes; 200V across diodes.) Thirdly, having a current-limiting resistor as shown before the load makes the output voltage rather heavily dependent on the load current. Suppose you have a 5-ohm I limiting resistor. Draw 5A and your output voltage drops by 25V! Some other circuits posted here, such as the emitter-follower types, are more appropriate. >-- >David E. Tiller davet@tsdiag.ccur.com | Concurrent Computer Corp. -- David F. Skoll | Department of Electronics | Opinions expressed here are dfs@doe.carleton.ca | Carleton University | my own and not necessarily (613) 786-7515 | Ottawa, Ontario, Canada | those of my employer.
reichert@motcid.UUCP (Charles H. Reichert) (10/19/90)
In sci.electronics you write: > 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!) Try using a 28VAC 2A Transformer in a "Bucking" mode on the Power Supply Input Transformer. This will drop the voltage to the range you need. Of course anything else hooked up will likewise be lowered so bypass these inputs unless they're off the same transformer, in which case you're stuck using this method. Another approach is to use some hefty Zeners... a string of 4 51V 400mA (or higher) Zeners in series from the DC output will drop the voltage. Chuck Reichert KD9JQ 708-358-3827 Home after 8PM CST 708-632-6669 Work
whit@milton.u.washington.edu (John Whitmore) (10/19/90)
In article <1990Oct18.134252.4635@mlb.semi.harris.com> jws@thumper.mlb.semi.harr is.com (James W. Swonger) writes: (basically a bipolar emitter follower on a zener diode regulator) It is important to diode clamp the base/emitter of the transistor, if the 600V supply has a filter capacitor (or power-down will kill the transistor) It is also a good idea to put a collector resistor into the circuit; if you KNOW you'll never need more than 200 mA, let the resistor dissipate the heat at full load. Also, power MOSFETs are available that can take the voltage drop this circuit will have; use them, they're cheap (and the bias resistors will dissipate a lot less power-the original was about 4 watts). Typical bias currents for 100V zeners are relatively low, so you can use them at much lower than 20 mA. The clamp diode for a MOSFET might be a zener diode (circa 30V) for more complete gate protection. The pass transistor is part of a 'floating' regulator, so there's NO need to have full 800V rated components; anything over 200V should do fine. Amended diagram: 800V+ --------------|------| | | > > power resistor; 1k ohm, 35W Limiting resistor < < (estimated peak dissipation: 20W) > > 2.2M ohms 1/8W | |- ~80 uA to bias zeners | || 350V rated power MOSFET +---|| | | at least 35W | |-+ (estimated peak dissipation: 10W) +-|<---+ | |____________ 600V+ | . . Stack of diodes with breakdown circa 600V . OR resistor for correct divider ratio | --- ^ /_\ | __|__ ///// John Whitmore
ih@udel.edu (Charlie Ih) (10/19/90)
In article <9510@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes: > >It is also a good idea to put a collector resistor into the circuit; .... > >Also, power MOSFETs are available that can take the voltage drop this ... > John Whitmore made an execllent suggestion and good analysis. This is probably the most practical circuits to use. However, if +, - 4% regulation (~ 575 - 625v) can be tolerated, a simple resistor will do the job. On the other hand, if you want to be very fancy and are not worried about costs and troubles, etc, a "switching" regulator can be used, as indicated below. This circuit is an overkill for this application. It may become practical for a larger voltage drop or for applications where the output needs to be changed (by changing R1, R2 and others). Suggested circuit: 800V+ --------------+------+ > | < | > | | |- | || +---|| | |-+ +-|<---+ | | | +-^^^^------------------------+---600V+ > /| | < /|-^^^--^^^+-----+----^^^^------| > /| | | | /| R1 R2 | +--^^^^^----| | ____/ | /|-^^^-^^^-+ | | 10v |/ /\ | /| | | | | Zener | | | | | /// | | ///// | | --- Capacitor | | | | --- | | +-----+ | | | | | 10v power | ///// | Reference | __+__ supply | | +| |------------ |-| |_____|__ Comparator/switching || | | circuit ||----------- + //// +-| | /////
pozar@kumr.UUCP (Tim Pozar) (10/21/90)
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!) How 'bout a number of zeners in series (with some current limiting of course). Or 286 silicon diodes forward biased (.7v * 286 = 200.2v) :-). Simple.... Tim --- uunet!hoptoad!kumr!pozar Fido: 1:125/555 PaBell: (415) 788-3904 USNail: KKSF-FM / 77 Maiden Lane / San Francisco CA 94108 "The nice thing about standards is that you have so many to choose from. Futhermore, if you don't like any of them, you can just wait for next year's model." -- Andrew S. Tanenbaum, "Computer Networks" (4.7.1)
tocherd@ul.ie (10/22/90)
Re using OA2 VR tubes in series - remember to put a high resistance in parallel with each one otherwise you will have striking problems with 'em. David Tocher University of Limerick Ireland
ssave@srvr1 (Shailendra Anant Save) (10/23/90)
From article <1990Oct18.134252.4635@mlb.semi.harris.com>, by jws@thumper.mlb.semi.harris.com (James W. Swonger): > > 800V+ --------------|------| > | | > > | > Limiting resistor ~ < | > 10K ohms (20mA base > | > drive, assume Hfe is | | / > >= 10. | |/ TV flyback (horizontal > +----| output) 1500V BVceo > | |\ at least 50W. Better to > --- | V parallel a couple with > ^ | emitter ballast resistors. > /_\ |____________ 600V+ > | > . > . Stack of diodes with > . breakdown ~ 600V > | > --- > ^ > /_\ > | > __|__ > ///// > > The stack of diodes to total a breakdown of 600V, would be a LOT of diodes, unless you mean zeners.... Here is one I can think of : ____________ 1| |3 +800V ________________| 7805 |______________+600V |____________| |2 | | | __|__/ / /\ / \ 195V Zener /____\ | | _|_ _ . Note that here, the o/p will be Zener volatage plus the last two digits of the 75XX series regulators. They have very good regulation and a good current capability (1 Amp.) The ground should be common on either side. You can use 7508 and use 192V Zener etc... Use a good heat sink. Also any other good feature of the 75XX is that they have thermal shutdown. Cost is about $2 at the Rack. (Radio Shack) --Shailendra ssave@caen.engin.umich.edu The University of Michigan Ann Arbor.
roy@phri.nyu.edu (Roy Smith) (10/24/90)
ssave@srvr1 (Shailendra Anant Save) writes:
-> ____________
-> 1| |3
-> +800V ________________| 7805 |______________+600V
-> |____________|
-> |2
-> |
-> |
-> |
-> __|__/
-> / /\
-> / \ 195V Zener
-> /____\
-> |
-> |
-> _|_
-> _
-> .
->[...] They have very good regulation and a good current capability (1 Amp.)
Unfortunately, you're asking the poor little 7805 to withstand a
in-out voltage differential of 200V! Even if it had a Vce,breakdown high
enough, you would still be asking it to dissapate 200W at 1A load. All
this will do fry the 7805 about as fast as you can throw the power switch.
What you really need is a 78H600 :-)
--
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy
"Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"
deanp@hplsla.HP.COM (Dean Payne) (10/24/90)
>From: ssave@srvr1 (Shailendra Anant Save) >Subject: Re: How to make 600VDC from 800VDC [picture of 7805 regulator and 195V zener deleted] Make that a 595 volt zener. > Note that here, the o/p will be Zener volatage plus the last >two digits of the 75XX series regulators. They have very good regulation >and a good current capability (1 Amp.) The ground should be common >on either side. You can use 7508 and use 192V Zener etc... Use a good >heat sink. Also any other good feature of the 75XX is that they have >thermal shutdown. Cost is about $2 at the Rack. (Radio Shack) The greatest fault of this design is that most 78xx parts have a maximum input voltage of 35V. Even an LM317HV adjustable regulator can handle only 60V. This design will apply over 200V to the regulator, smoking it. As drawn, the regulator would reach its internal thermal shutdown at a lower output current than the requested 150-200mA, even when attached to an infinite heat sink.
phys169@canterbury.ac.nz (10/29/90)
From article <1990Oct18.134252.4635@mlb.semi.harris.com>, by jws@thumper.mlb.semi.harris.com (James W. Swonger): [circuit using "stack of diodes with breakdown of 600v"] In article <1990Oct23.151030.5176@engin.umich.edu>, ssave@srvr1 (Shailendra Anant Save) writes: > The stack of diodes to total a breakdown of 600V, would be > a LOT of diodes, unless you mean zeners.... > [goes on to use 78xx series regulator well beyond it's voltage rating] The first circuit was best, but the reference voltage can be derived in better ways. One way is a bunch of neon bulbs in series (with 1Mohm resitors across each one - about 90volts/bulb from memory) but you need another transistor to get enough current into the base of the transistor, and a capacitor to smooth out nasty jumps in base voltage as the neons fire. If great regulation isn't required, the regulator could simply chop off 200v (less zeners or VR tubes, etc). Or a resistor divider could feed the base of the transitor (still better regulation than a potential diver straight into the load). But my favourite (avoiding a 600v reference) is... 800V+ --------------|------| | > R3= > < R2= 160V/Imax (limit power in transitor) R2*HFE < > (approx 50W) > | | | / | |/ TV flyback (horizontal +----| output) 1500V BVceo, | |\ at least 40W. > | V R6= < | R3*550/200 > +----+-----------> 600V+ | C1__|__ > \ | _____ < R4 ~ 100K/5Watts \| | > ( <<R3*HFE2*579/200) |----+----| /| | V < | > R5=R4 * 579/21 ----- < ^ ' 20v | /_\ zener* | | | __|__ __|__ ///// ///// Notes: (1) Use 2*10Volt low power zeners in series if you like. (2) C1 is optional; try 200nF/800Volt - larger capacitor for slower start-up, if you omit it, put at least a 1uF capacitor across the zener to reduce noise in the power supply line - zeners can be noisey, and we're going to magnify any noise by a factor of 30 otherwise). C1 is essential if you have a big power supply capacitor on the 600v side of the circuit. (3) Second transitor needs to be able to withstand at least 800V, 12Watts. (4) remember an insulated heatsink for the main power transistor. (5) R2 & R6 are there basically just to reduce heat in the transitors, and to limit currents. (6) Be careful with the high voltages. (7) If the 600V load has a large capacitor, but the 800v supply doesn't (but has some other equipment sucking current, be careful when switching off the power that the main transistor doesn't become temporarily reverse biased - you may need a protection diode. (8) E&OE (I haven't actually tested the circuit, but I've built similar ones) Mark Aitchison, University of Canterbury, New Zealand.
phys169@canterbury.ac.nz (10/31/90)
In my article <1990Oct29.152553.9568@canterbury.ac.nz>, phys169@canterbury.ac.nz writes: > > | V > R6= < | > R3*550/200 > +----+-----------> 600V+ > | C1__|__ > > \ | _____ < R4 ~ 100K/5Watts > \| | > ( <<R3*HFE2*579/200) > |----+----| > /| | > V | < > | > R5=R4 * 579/21 > ----- < > ^ ' 20v | > /_\ zener* | Whoops! Sorry, folks, R5= R4 * 21/579. (Thanks, Curt, for pointing that out). Us antipodean people tend to get things upside down. By the way, you may need a small variable resistor in series with R5 to provide fine adjustment of the voltage, and to compensate for base current spoiling the output voltage calculation. This basic circuit is good where the voltage drop required is relatively large; there is a nice modification of the circuit for situations where the voltage drop required is small (or a wide range of output currents is envisaged), which involves having the power transistor's collector at earth potential (good for heatsinking many power transistors where the case is connected to the collector)... ask me if you want the circuit. Mark Aitchison.