regulated screen supply

[modulation_apprentice]

i was wondering if anyone could give me a link or somewhere would i could find some reading on regulated screen and or grid supply's. All the books i have here are old and use vr tubes.

[Opcom]

you want solid state or a tube kind that is an actual series regulator?

What voltage and current?

Do you expect "negative screen current" as can occur with a RF amplifier?
If so, how much does the supply need to sink?

[modulation_apprentice]

i'm wanting to see how to do it with new solid state parts.

i do not really have anything specif just an in general idea of how it would work.

[Opcom]

An N-channel enhancement mode MOSFET rated for the highest voltage you can find would do well for the pass stage. But I am not familiar with designing with those. Should behave like a tube in the same situatiuon though. One thing people do when faced with regulating a higher voltage than the solid state parts will stand is to put an unregulated DC suppy in series with the regulated one and take the error from the entire output.

here are some schematics;

this one shows how to do current limiting but I don't thinkit's regulated well:
http://www.elecfree.com/electronic/power-supply-0-300v-dc-adjustable/

190-320V 50mA
http://www.elecfree.com/electronic/power-supply-regulator-190-320v-50ma/

this is a high voltage amplifier. It could posibly absorb any reverse current.
http://www.edn.com/article/CA468423.html

[modulation_apprentice]

thanks for the links

[WA1GFZ]

my V2 CDC I mounted 3 isolated 10 watt zeners with insulating hardware on a 1 X 1 aluminum angle bracket. The three add up to the voltage you want to run on the screens) On the other side I drilled two holes for a terminal strip. These holes were then drilled in the V2 chassis in place of the slider and mounted with short self tapping screws. Be careful not to damage the roller inductor above the chassis. I wired the 3 zeners in series with 3 200 k 2 watt balance resistors. (also bleed the HV) Then mounted a 25 k 20 Watt WW across the terminal strip. This goes in series with the  top stud of the zener stack and modulator screens. The other end of the resistor goes to modulated B+ and the bottom stud zenor goes to the DC return (not ground). Holds the screen voltage solid even with atomic yealows. This fits right in place of the slider.
Zenor regulated grid. Just hang a zenor between the driver transformer CT to chassis. Remember this is a negative voltage so terminal goes to ground and stud to ct.

[KM1H]

I havent reached the point of trusting SS in HV above about 400V. For serious screen voltages and current, a series string of zeners as a refernce for a shunt 811A are about as foolproof as it gets. The tubes can be paralleled for more current or use a 572B. Regulation is held to the tubes grid to ground drop which is around 10-15V at 1000-1500V.

This also works well with oldies style self excited oscillators such as PP 211's to regulate the plate voltage and get rid of the yoop on CW.

Carl
KM1H

[WD5JKO]

here are some more links to three more solid state HV regulators. These have been working now for about 5 years without issue. They are short circuit proof when you turn power on with a short. I was too chicken to try that once power was up.   


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

73,
Jim
WD5JKO

[Ed-VA3ES]

Here's another one. Touted as a "Solid-State Filter Choke or Field Coil Replacement ", but will work as a solid state regulated screen supply, which is what I will use it for.

http://www.antiquewireless.org/otb/resto0504.htm

[WA1GFZ]

bull pucky a properly designed zener regulator will last forever and take a lot less space and be more stable.

[WD5JKO]

We need to keep several things in mind when we are playing with voltage regulators. It is important to define what you are looking for. Here are a few:

1. Ripple reduction of the incoming power. A single series pass element can provide 50-70 db of power ripple reduction. 

2.) Line voltage regulation. Vary the AC line from say 105 to 125 vac and maintain constant output.

3.) Load current regulation. Vary load from min to max to maintain the output voltage constant.


Misc:

  If you look at my circuits, I use a CCS (constant current source) which improves ripple reduction, and increases gain (375v regulator). I specify part numbers, but a better part might be the Supertex LND150 which is a 1-3 ma CCS 500V depletion mode fet. There is a huge difference between the CCS and a resistor.

http://www.supertex.com/pdf/datasheets/LND150.pdf

  High voltage zener diodes have a significant temp drift where the voltage increases as they warm up. This is of little concern if you don't care if the voltage drifts upward 5-10% after a cold turn on. A VR tube is actually much more stable than a HV zener diode.

A 6.2v zener rises 2.2mv / deg C, and a silicon diode decreases the same amount. Combine the two, and feed with a CCS, and you have a very clean and stable voltage reference. It will usually stay within 0.001v when the two are thermally bonded together. My 375v regulator takes advantage of the stability of the 6.2v zener. The silicon diode is actually the B-E junction of the MPS-U10 error amp transistor. So dividing the HV down to 6.2v at the error amp works just fine, and if the reference is stable, and the resistors are metal film, then the HV will be very well controlled and stable.

Here is a vacuum tube screen regulator I designed and built. This regulator doesn't budge, and meets 1, 2, 3 above very well. I show a 5V6 on the schematic, but it is better with a 6W6:

http://pages.prodigy.net/jcandela/Central%20Electronics%2020a%20QRO%20%232/CE_20A_QRO_Power_Supply.jpg

Jim
WD5JKO

[WA1GFZ]

put a tube and stud mounted zener on a shock table and place your bets.
I've never worn out a zener.

[WA1GFZ]

Well if we are talking about EMP maybe I agree. Tubes are nicer to look at but a good solid state design may live longer. There is that emission issue.