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0-30V Stabilized Power Supply


redwire
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20v transformer it is. Now just a few quick questions before I order parts because of some parts list and schematic conflicts:

1) Schematic shows a 100nf poly cap (labeled C10 on some schematics) between the negative line and the emitter of transistor Q3 & opamp U3's Vcc, but is not on parts list, should this be removed completely?

2) Resistor R15 (100 ohm) is nowhere to be found on schematics, delete?

3) The 10v 1w Zener is missing from my parts list, but this should be added right? There should be a 5.6v and 10v Zener?

Thanks again for your guidance.

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1) Schematic shows a 100nf poly cap (labeled C10 on some schematics) between the negative line and the emitter of transistor Q3 & opamp U3's Vcc, but is not on parts list, should this be removed completely?

When I added the 10V zener diode to reduce the supply voltage to Q3 and U3 I added the 100nF capacitor because all opamps need a supply bypass capacitor. But I forgot to number it.

2) Resistor R15 (100 ohm) is nowhere to be found on schematics, delete?

The oroginal schematic used R15 but it was useless. Delete it.

3) The 10v 1w Zener is missing from my parts list, but this should be added right? There should be a 5.6v and 10v Zener?

The 10V zener diode is important. The 5.6V zener diode D8 is extremely important and should be one that is rated at only 5mA. Many zener diodes are rated at 45mA and should not be used.
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The BD139 is in a very old case so its thermal resistance is high (it is difficult to cool).
The 2N3055 output transistors have a lot of power to dissipate.

It is easy for you to calculate the max power of a transistor, look up its max allowed temperature, decide how high you want the max temp to be, allow thermal resistance for insulators then select a heatsink.

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hello,
I would like to replace R7 with a shunt resistor of 0.0075 Ohm,
I assume this will have an effect on R17 & R21.
P2 should stay 10k (I already have this one).

-How can I calculate the new resistorvalues?
-R7 limits the max possible (short cut) current in the circuit, maybe I could increase the resistors at the 2N3055 output to ie 1 Ohm to compensate for this?

thanks

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I would like to replace R7 with a shunt resistor of 0.0075 Ohm

The pcb traces will add a lot of unknown resistance and will destroy the accuracy of the current setting.
3A in only 0.0075 ohms produces a voltage drop of only 22.5mV which is fairly close to the input offset voltage of U3 so some ICs will read the current as being much too low and other ICs will read the current as being much too high. At lower current settings you will not know how much is the current regulation.

-R7 limits the max possible (short cut) current in the circuit

No.
R7 does not limit the current, the circuit limits the current. R7 simply senses the current.
Your idea makes no sense.
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  • 2 weeks later...

I built this power supply a couple of years ago and have used it for a variety of tasks.  Tonight I was using it to try to run a 12v motor (around .5A) but the motor seems to have a problem (perhaps shorted) and now my power supply isn't supplying any power.  There is power to the board from the transformer.

What would be the most likely component to have blown?

Should I have added a fuse somewhere?

Philip
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Sorry - so far as I can see, my device uses the current circuit.

I have built a few electronic devices but all of them have worked fine.  I would know how to test resistors, the transformer (which is working fine) and rectifiers but not sure how to test transistors.  How can I do that?

Philip
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A transistor can be tested with a new digital multimeter.

In the low voltage ohm-meter function that supplies only 200mV so the juctions do not conduct, the collector to emitter should not conduct and the reverse-biased base-emitter and base-collector diodes should not conduct.
In the "diode-test" fuction, the forward-biased base-emitter and base-collector diodes should conduct.

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  • 2 weeks later...

Audioguru,

I have replaced the power transistor (Q4), R7, Q1 and tested with a (just purchased) multimeter to see whether any of the capacitors are non operational but still no output from the power supply. I don't think any of these were blown but they seemed to be likely candidates, so replaced them.  Not sure what to do next.

Would the op amps be the problem? If so how can these be tested? Replacing them?

Thanks,

Philip
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U2, Q2 and Q4 are an amplifier with a voltage gain determined by the values of R11 and R12. R11 is 27k and R12 is 56k so the voltage gain is 1+ (56k/27k)= 3.074. The trimpot reduces the gain to be low enough so that the max output voltage is 30.0V when the voltage pot is set to max and has 11.2V from U1.

Measure the output of U1 and it should always be close to 11.2V. It feeds the voltage-adjust pot.

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  • 2 weeks later...

Heya, I'm going to make this project. My question is, does everything work and are there any nesessary modification in the project posted here?

You are looking at the original project that is (was?) a kit in Greece. It has many errors that cause it to fail because the supply voltage for the opamps exceeds their max allowed supply voltage, the transformer and output transistor are overloaded and the old driver transistor is severely overloaded.
Its rectifier diodes and some of its resistors are also overloaded.
It cannot produce 30VDC at 3A. Its max output is 24VDC to 25VDC with lots of ripple at 3A.

In this forums section of this website we corrected it.
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I looked up trough this topic, and as s final result I'm pretty much confused. There are a lot of question and answers, different version of the schematic and so on. I's hard for to find real working scheme with ready echable board (my english is not perfect and that makes problems...). My appeal is to link, a working version with the nesessary files, which i can use to build the board ( a ready printable file will be great). I can be single or double sided,but single sided is prefered. 
Thanks!!

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I looked in your project, and I have some questions. Can 24V input from transformer be used?
And can 2N3055 be used instead of TIP3055?

Yes a 24V transformer can be used but you will not get the full 30V plus you will suffer a higher ripple at max voltage set to max current, This would be ok if only want 25V PSU
Yes you can use 2N3055 instead of TIP3055

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31.5VAC has a peak of 44.5V. The rectifier bridge and main filter capacitor will produce an unregulated positive supply of 43V for opamps U1 and u2 which is close to their max allowed supply of 44V. If the mains voltage is a little higher then the opamps might fail.

A 28VAC (at full load) transformer will work well and be safe.
Hammond in Canada make a 30VAC transformer that is 31V without a load.

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