[sci.electronics] How to make 600VDC from 800VDC

(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.