High Voltage Regulator design

[rblilja]

Hi all,

I need to provide my tube amp with 220VDC. The nominal current will be about 43mA.

What I want to do, is to regulate 320VDC (full wave rectified from transformer) down to 220VDC (the ability to adjust the secondary voltage would be great). My initial idea is to use a zener-diode together with a MOSFET or alike. Can anyone advice me how to design such a circuit?

Simplicity is prioritised over efficiency (in this case at least).

Thanks.

// Robin Lilja

 

[karesz]

Hi,
As some start idea for you:
50v to 120volt power supply 2A, #1286468
K.

 

[rblilja]

Would it be possible to just change the zener diode to a 220-230V one in the MOSFET power supply design found here..

**broken link removed**

I should probably make sure that there's enough current flowing through the new diode by changing the 6.8k resistor?

How about to make that one adjustable around the zener voltage?

 

[karesz]

Hi Robin,
I think, its not a problem, but as I know Zeners are at 150V out= you must compose that from 2-3 diodes, so is the relative big tolerance no problem too...
In all case you have to select some other FET, these has Uds=max.160V...
Than dont forget a 12V Zener for G-S clamping.
For some variability I would apply a higherohm Poti (maybe with a serial resistor too) on the Zener and contact the slider to the gate...
I think, that a current limiter to have isnt so bad idea too.
K.

 

[rblilja]

Thanks for your fast reply!

I refined my keywords when searching for schematics and came across this second design - more or less the same as the previous one. Somehow this one appeals me a little more.

**broken link removed**

I think I will put in one 130V and a 100V (230V in total since the output will drop a little) zener and change R2 to 47K for increased current (~5mA) through the zener pair. Is it a reasonable modification?

The reason why I'm almost asking the same question again is due to the fact of the nasty voltages involved here. Better safe than sorry.

Thanks again!

 

[karesz]

Hi Robin,
BE CARE with HIGH VOLTAGES_at these ENRGY ITS VERY DANGEROUS!!
How much wil be the input DC on C3, am I correct, that you assumes it at ca.280V?
Your 5mA=UC3-Uzener, divided with R2...
K.

 

[rblilja]

I simulated the circuit in LTSpice. The DC is about 320V since our mains here in Sweden is 230VAC. I will step it down to 12VAC and then step it up to 230VAC again. The 12VAC will be used for heating the filaments.

320-220 / R2 = Iz in rough figures.

Changed my mind regarding the selection of zener diodes, my solution now contains three 75V zeners and R2 is set to 20K. I will try (with big precousion) the circuit during the weekend.

Best regards.