# Zener Diode question

Discussion in 'Amp Tech Center' started by spoontex, Oct 8, 2017.

1. ### spoontexTDPRI Member

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I want to build this cirucit:

http://www.r-type.org/articles/art-010g.htm

But, I don't understand how he gets the values of R2, because I can't get matched values.

If I require an output voltaje of 150V, I get five 30vf zener.

Vin=240
Vout=150
mA= 36
R2=x

R2= (240 - 150 ) /36 = 2,7K

Prs= (250 - 150 ) x 36 = 3,6mW

What I'm doing wrong?

2. ### RLee77Friend of Leo's

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So a few problems with your calculations… if you read the text of the article closely, you'll see that the rectified dc voltage is 340vdc, and you used the 240vac rms value instead of the dc output. (To convert ac rms volts to peak, you multiply by 1.414)
Once you correct for that, you'll get correct values. Also, when you did the power calculation you wrote the wrong units, should have been watts, not milliwatts (as well as the numbers being off because of the previously mentioned dc vs ac issue).
The article itself is a bit dated, as there are plenty of hi voltage transformers and electrolytic caps available from many sources.

3. ### spoontexTDPRI Member

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You are right, but

(340 - 150) / 36 = 5,27

And what is R1?

And the last question. How can I test the circuit without the load? I need a load resistor? And what values?

Thanks.

4. ### RLee77Friend of Leo's

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R1 is there to safely drain the filter caps when the supply is switched off. Otherwise a hazardous hi voltage would remain once the voltage dropped below the zener clamp threshold.
For a load, just figure the R needed for 30ma at 150v. And mind the wattage needed for R2 and the load, and the zeners as well.

There are better regulator designs easily available via a google search, that use a series pass device that allows the zeners and resistors to operate at a much lower power, if you're interested.

5. ### spoontexTDPRI Member

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Thanks.

Yes, I want build a power supply for a phono tube preamp. The htc needs a voltaje between 250 - 300 vdc and a maxim of 20 - 30 mA. I found this shematic, but if you says that nowadays we have better solutions. Please tell me.

Thanks again.

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