Help me mod simple zener regulator

rotation · 15th October 2009, 08:09 PM

Hi,

i would like to build this simple regulator:
Audio Amplifier | Regulated Vacuum Tube Power Supply
The problem is that my secondary (no CT) have 230V, so i get around 315VDC after gretz. So if i want around 260-280 out of this psu i should scale 5W/10k resistor. What value do i need to get 5mA through zeners at all times? Is 5k ok if highest wanted out voltage is not more than 280VDC?
Also, how big can cap near zener can be? Wouldn't it act as a capacitance multiplier? Someone say it takes away zener noise, i'm confused, i thought it's multiplier..

Thanks, Miha

peranders · 15th October 2009, 08:34 PM

R = (Uin-zener voltage)/I where I is 5 mA

The cap at the zener is rather useless. It's better to add a LP-filter after the zener. The resistor should have a rather little voltage drop and corner frequency should be 1-10 Hz.

How much current do you plan to take out from the regulator?

Do you use TIP50?

cerrem · 16th October 2009, 01:41 AM

Keep in mind that this is a overly simplistic power supply with poor regulation....
This also depends on what you define as good regulation.....
This is open loop regulator.... The capacitor across the zener acts as a soft-start in conjunction with the resistor in series with it... You have the RC time constant of this Cap with the resisitor and any resistance behind it added up.... Then once you arrive at the Zener breakdown voltage the cap is not much use, possible some small filtering of the zener but not much... There is no protection diodes to protect the pass transistor durring turn-OFF .... You need one from emitter to base and one from emitter to collector.. Just in case so you don't blow the BJT when yo shut down the power transformer...
The Zener should be feed from a current source for more accuracy... such as a PNP ..
ALso depending on the Worst Case Beta of the Pass transistor you will have variation of current on the zener string..also not acceptable for a good regulator..
You can improve the output imedance of this open loop regulator by using a darlington configuration on the pass device..just use the same device twice....

Best Regards
Chris

rotation · 16th October 2009, 08:50 AM

Hi,

thanks for replies. I'm not sure if i really need regulation because i never heard improvement in sound with it and i tried several designs. That's why i went with this simple regulator. I used to use regulators based on TL783, but found them to be too sensitive for my experiments, they blow quite fast.
I'm using TIP50 as per schematic, currents and voltages are different, depending on what i'm building. Normally i need from 250-280VDC at 10-25mA.
I will add those diodes and make darlington at the output, as suggested.

Miha

15th October 2009, 08:09 PM	#1
rotation diyAudio Member Join Date: Oct 2005	Help me mod simple zener regulator Hi, i would like to build this simple regulator: Audio Amplifier \| Regulated Vacuum Tube Power Supply The problem is that my secondary (no CT) have 230V, so i get around 315VDC after gretz. So if i want around 260-280 out of this psu i should scale 5W/10k resistor. What value do i need to get 5mA through zeners at all times? Is 5k ok if highest wanted out voltage is not more than 280VDC? Also, how big can cap near zener can be? Wouldn't it act as a capacitance multiplier? Someone say it takes away zener noise, i'm confused, i thought it's multiplier.. Thanks, Miha

15th October 2009, 08:34 PM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	R = (Uin-zener voltage)/I where I is 5 mA The cap at the zener is rather useless. It's better to add a LP-filter after the zener. The resistor should have a rather little voltage drop and corner frequency should be 1-10 Hz. How much current do you plan to take out from the regulator? Do you use TIP50? __________________ /Per-Anders (my first name) or P-A as my friends call me

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16th October 2009, 01:41 AM	#3
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	Keep in mind that this is a overly simplistic power supply with poor regulation.... This also depends on what you define as good regulation..... This is open loop regulator.... The capacitor across the zener acts as a soft-start in conjunction with the resistor in series with it... You have the RC time constant of this Cap with the resisitor and any resistance behind it added up.... Then once you arrive at the Zener breakdown voltage the cap is not much use, possible some small filtering of the zener but not much... There is no protection diodes to protect the pass transistor durring turn-OFF .... You need one from emitter to base and one from emitter to collector.. Just in case so you don't blow the BJT when yo shut down the power transformer... The Zener should be feed from a current source for more accuracy... such as a PNP .. ALso depending on the Worst Case Beta of the Pass transistor you will have variation of current on the zener string..also not acceptable for a good regulator.. You can improve the output imedance of this open loop regulator by using a darlington configuration on the pass device..just use the same device twice.... Best Regards Chris

16th October 2009, 08:50 AM	#4
rotation diyAudio Member Join Date: Oct 2005	Hi, thanks for replies. I'm not sure if i really need regulation because i never heard improvement in sound with it and i tried several designs. That's why i went with this simple regulator. I used to use regulators based on TL783, but found them to be too sensitive for my experiments, they blow quite fast. I'm using TIP50 as per schematic, currents and voltages are different, depending on what i'm building. Normally i need from 250-280VDC at 10-25mA. I will add those diodes and make darlington at the output, as suggested. Miha

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