Idea(s) for simple HV regulated psu

[rotation]

Hi!

I need to build simple HV psu for experiments with tube preamp circuits (mostly mic preamps). Since it is for experiments i don't need very good regulation or low noise.
I already used Maida regulator with LM317 and Gyraf's regulator with TL783. They are ok but a little too complicated (or expensive if with TL783) for this task.
So i thought about using this one:

http://www.electronicsinfoline.com/P...r_supply.shtml

I normally use 220:12-12:220V transformers to avoid buying custom transformers, so i get around 310dc after rectifier.
My projects need from 250-300vdc and never more than 30mA of current.

So, i have a question about regulator from link:

How do i calculate 10k/5W resistor if i need, say, 280vdc/25mA?
When i calculated output current from the regulator on this link, i get very low numbers, from 5-10mA.
Well, i don't know exact difference between in/out voltage, but from what guy says it must be somewhere between 50 and 100V...

Also, somebody told me that capacitor in parallel with zener diodes shouldn't have more than 10uF, otherwise zener can burn. Is that truth?

Regards from Miha

[Richard Ellis]

How about this set-up?, similar to what your after.
With a straightforward isolation transformer,full-wave bridge and say a 20,000 uf cap (Has good ripple rejection)........more quiet than your posted PS, as mic preamps should be very quiet.
______________________________________Rick........ .....

[rotation]

Hi,
i've seen this one before. The problem is that i can't get LR8N3 regulator locally.
I will use this regulator mostly for experiments, so i don't need very low noise or very good regulation.
Can anyone explain me what's up with 10k resistor from my link? I would like to understand and probably build it.

Miha

[Sal Brisindi]

Here is a link to a very simple 0-330vdc solid state power supply I wanted to build but with 3 tube based adjustable high voltage power supplies, well I never got around to build it.

http://www.geocities.com/tjacodesign...p/300vsup.html

Regards,
Sal

[rotation]

Hmm, i'm coming back to this one all the time
I will build it and see what happens, thanks.

Miha

[DougL]

Can anyone explain me what's up with 10k resistor from my link? I would like to understand and probably build it.

The Zener string in the example is 5 * 60V zener diodes.
if the unregulated supply is 350V, the resistor has 50 volts across it. Using ohms law, we need to pick a resistor value that will allow enough current so the zener string has enough current so it is at full voltage and is (relatively) quiet but within the 5w dissipation limit for each 60v zener.

Since 10k across 50 volts is about 5 mA, seems like a good choice.
To check, 60 volts * 5 mA = .3 Watts

Just guessing, the transformer you chose is not going to work well for 300V. I would guess about 280 Volts is about max, and you may need to adjust the "10K" resistor to furnish more current if there is a lower voltage.

HTH

Doug

[Stixx]

How do i calculate 10k/5W resistor if i need, say, 280vdc/25mA?

Doug gave a good explanation on the resistor.
Output voltage is set by the string of zeners.. so in your case you just have to add up zeners until you arrive at 280V... like 4x60V and 1x42V gets you close enough.

Well, i don't know exact difference between in/out voltage, but from what guy says it must be somewhere between 50 and 100V...

I'd say no more than 50V.

As for the capacitor 1uF should be okay, 1uF/400V that is.