~700vdc regulated supply

[rsumperl]

Greetings everyone,
      Does anyone have a schematic for a relatively simple, but effective 700vdc regulated supply? I'll need to pull ~250ma.

Thanks,
 Ray

[WD5JKO]

Does anyone have a schematic for a relatively simple, but effective 700vdc regulated supply? I'll need to pull ~250ma.

  Ray,  Do you want tubes or solid state?

Questions:

1.) line voltage regulation?
2.) Load current regulation?
3.) Ripple reduction?
4.) How much voltage drop can you accommodate if the regulator is a linear series pass type?
5.) What is the Peak to Peak ripple amplitude on the raw supply at 250 ma load, and how low is the dip in the ripple when the AC line is at minimum, say 110 vac?
6.) Does the supply need to survive a short circuit?
7.) Just curious, what is the application?

Jim
WD5JKO

[rsumperl]

Jim,
  I am not too concerned about great regulation, perhaps within 5-10%. Don't really care if solid state or tube, will never see a short circuit, so short circuit protection not needed. Not greatly worried either about line regulation. Just would like something that if the load varies let's say between 50 and 250ma, that I won't have large swings in voltage.

Thanks,
 Ray

[rsumperl]

Forgot to add, that I'm not greatly concerned about ripple reduction.

Ray

[WD5JKO]

Ray,

   It sounds like your application is ripe for a good old fashioned choke input filter with a sufficient minimum load via a beefy bleeder resistor. I'd make sure the final 'C' is at least 100 mfd to minimize weird gyrations that may occur if the load, or unload excites the main L-C resonant frequency.

   A step further is to resonant the choke (if a smoothing type) for added regulation and ripple reduction. That cap would need to be a big job, preferably oil type, adjusted at the high side of 120 hz, and maybe have a resistance in series with it (a 100 ohms or so) if the choke has a very low DCR. This will lower the 'Q' somewhat. One combo would be .4 uf and 4h. I'd go for whatever choke you have that might work..

   I'm known to regulate all sorts of stuff, but your description does not sound like you need active regulation....

If you do want a series regulator, can you afford to provide at least 900v at the dip of the ripple amplitude?

Look at schematic 600L_2.jpg:
http://bama.edebris.com/manuals/ce/600L/

This uses an 812 pass tube to make 500-680v from a high B+ of 1800v. A pair of 812's might do 250ma as long as Vin - Vo is > 200v and < 500v.


Jim
WD5JKO

  

[vk3he]

Hi Ray

Look in the ARRL Hanbook 1968 page  320.

Regulated screen supply  500 to 700 volts by W9OKA. Its a tube regulator.  There is also a circuit for a 850 volt to 1500 volt screen tube regulator.
There is another  a 750 volt shunt screen regulator in the same Handbook using VR150's and a 811A.

This Edition of the Hanbook has a good discussion on regulated high voltage supplies.

Rich Measures has a good solid state circuit on his web page. I have experimented around with this regulator on a 4-1000, its a bullet proof design.
The GM3SEK screen regulator might be able to be modified with external components. Contact Ian.

Theres many ways to skin the cat or rabbit depending on your taste!

Craig

[WU2D]

Hi Ray,

I have been using bipolars and mosfets in very simple follower regulators up to 500V without many issues. No reason they should not scale up because there are cheap high voltage devices out there.

Mike WU2D

[WA1GFZ]

IGBTs come in higher voltage ratings than FETs and Transistors

[WD5JKO]

Ray,

    The following link illustrates some solid state regulators that I put into my old Sherwood S8000 Hi-Fi tube amp. This has been working without issues for 6 years now.

http://pages.prodigy.net/jcandela/Sherwood_S8000/HV_REG/S8000_Mods2.htm

    I believe that both my circuits and the one Mike just posted will be lucky to survive a short circuit. My approach differs from Mike's. Mike uses a downstream current limit such that the limit value forces the FET in the linear range with high V * I dumping heat in the FET. The 1 amp upstream fuse only blows when the FET shorts out. In my case I have a 51 ohm resistor at the drain of the series pass FET. The idea is to provide a hard saturated bias on the FET to keep the FET RDS on at minimum value during a short circuit until something upstream like a series resistor or fuse pops. The hope is that the FET survives the storm. I was too chicken to test my circuits once powered up. I did test them with power off, short the output, and variac up the power. The circuits worked as intended. Still taking a screwdriver to the full regulated B+ will likely result in melted silicon.

    Take notice of my use of constant current sources. These dudes can really enhance a regulator circuit. I used older parts as a CCS, but the Supertex LND-150 is a 500v rated deplation mode FET which has a IDSS rating of about 2ma (min 1ma, max 3ma). This is often ideal for feeding a string of zener diodes.

click on depletion mode mosfets:
http://www.supertex.com/products/selector_guides

Jim
WD5JKO