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# 0-30V Stabilized Power Supply

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Cann I use an  C1 = 4700

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Many of the parts in the original project are too small so they over-heat, especially the tiny 2N2219 transistor that is used for Q2. Even the transformer is too small so it also over-heats.
The transformer voltage is too low so the project will never produce 30V at 3A.
The opamps have a max allowed supply voltage of 36V but it is 38V or more in this project with the transformer voltage too low.

I think the main filter capacitor should be 12,000uF.

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Assuming. a 30V transformer, a regulator drop out of 6.4V (going from what you said), a rectifier loss of 2V and an output voltage of 30V with a 3A load, I calculate the minimum filter capacitance to be 6521

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The 0.47 ohm current-sensing resistor has a voltage drop of 1.41V at 3A.
The transistors and U2 opamp have a range of voltage drop at 3A.

Also, the value of the main filter capacitor has a wide range.

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i have a 25V 8,33A Transformator

25*1,41 = 35,25V ???

Changes:
C1 = to 4700
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You need a 30V transformer.

C1 needs to be at least 6800μF, preferably 10,000μF for 30V@3A out.

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The original circuit uses opamps that have a max allowed supply voltage of only 36V and two of them also use the -5.6V negative supply. The 30VAC transformer will be 31VAC without a load and will produce an unregulated +42.4V supply. Therefore two opamps will have a total of 48V as their supply.

3A rectifier diodes will get too hot (they don't need to be 600V).
Q2 must be an NPN but a BD140 is a PNP. Use a BD139 instead on a medium size heatsink.
use two output tranaiators, each with a 0.33 ohm emitter resistor.
many of the resistors are too small and will get to hot.

That is why we modified the circuit to make it work properly and to make it reliable.

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ok i hope i can find the MC34071 OPAMP

i will use max  30V@2A

how much Volt i can get with a 24V Transformer ?

i change the OPAMP to MC34071 if i can find it.
an change the 2n2219 to BD139 on a heatsink

I build 4 Supplys in a Box i can put all the BD139 on a Heatsink

will it work fine after changing Parts i hope the ripple is not to big

can i use the shematic on the main side ?

how shematic i have to use.. i have used this

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We modified the circuit so that MC34071 or TLE2141 opamps can be used with a 28VAC or 30VAC transformer. If you use them in the original circuit then they will have a total supply voltage of 39.6V and will be fine since their max allowed supply is 44V.

But there are many other things wrong with the original circuit.
With your 25VAC transformer, 4700uf capacitor and a 2A load, the max output will be about 25VDC with a lot of ripple, maybe 23VDC with no ripple.

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now i am confused:

i will build the supply

1. I have an 24V Transformer witht 8,33A
2. I have the PCB(done) with the old circuit
3. I have to change parts in the circuit
4. I would use the TL081, BD140 in the old circuit
5. I take two 4700

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The max allowed supply for the TL081 is only 36V but in your circuit U2 and U3 will have 39.4V when the circuit has no load.

The resistor (R10) for the input offset voltage adjustment pot (RV1) is the wrong value and connects to the wrong voltage.

If your transistors have a high gain then you will have 24VDC at 2A with low ripple.

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• 2 weeks later...

:) Hi I have a question for you Audioguru, Why did you eliminate the transistor Q1? I saw this function was protect the output circuit we are testing when the power input is disconected ( I mean the discharge from capacitors).
Another question I built two upgraded circuits and works pretty well (whit LCD

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:) Hi I have a question for you Audioguru, Why did you eliminate the transistor Q1? I saw this function was protect the output circuit we are testing when the power input is disconected ( I mean the discharge from capacitors).

The TL081 opamp has the problem called "Opamp Phase Inversion" where its output suddenly goes high when its negative power supply voltage becomes close (within about 3V) to its input voltages which happens in this project when the power is turned off. Q1 shorts the output of U2 to 0V to prevent it from going high when the negative supply quickly drops to less than -3V. The MC34071 and TLE2141 opamps do not have the problem since their inputs work perfectly when the negative power supply voltage drops to 0V.
Nothing in the project discharges the capacitors.

Another question I built two upgraded circuits and works pretty well (whit LCD

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I intend to replace transistors Q2 and Q4 with single TIP142, which is darlington type. I hope it's OK?
Should this still work flawless?
I've got OPA445 opamps and with transformer 45V i'll have input voltage of 65V, and i'll set max. output to 50V. i'll use AVR instead of potentiometer for voltage control. is there anything else i should be carefull about (except all parts must be for such high voltage, of course)?

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I intend to replace transistors Q2 and Q4 with single TIP142, which is darlington type. I hope it's OK?
Should this still work flawless?
I've got OPA445 opamps and with transformer 45V i'll have input voltage of 65V, and i'll set max. output to 50V. i'll use AVR instead of potentiometer for voltage control. is there anything else i should be carefull about (except all parts must be for such high voltage, of course)?

If the output is set to a low voltage or is shorted then the TIP142 will melt trying to dissipate 195W.
Your supply voltage is so high that nearly every other part will also get too hot.
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OH, i forgot to mention that i'll be using pre-regulation circuit, so input will be appr. 5-7 V higher than output

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can I do an series connection with 2 Supply to get +-30V ?

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OH, i forgot to mention that i'll be using pre-regulation circuit, so input will be appr. 5-7 V higher than output

Then the pre-regulation circuit will melt trying to dissipate up to 177W.
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can I do an series connection with 2 Supply to get +-30V ?

Yes, if each power supply circuit is completely separate from each other with separate transformers.
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Then the pre-regulation circuit will melt trying to dissipate up to 177W.

pre-regulation will be switching type, with mosfet, so no dissipation will be on that part (schematic was published in elektor magazine years ago, i already tested it and works great). I'll put 65V to opamps, while collector of power NPN will be via this switching pre-regulator. I know i'll have to recalculate some parts, especially some resistors, i think. I just wondered if you ever tried it with such high voltage. After all, that's why i've got OPA445. I tried with MC34074 and other schematic (which works for years with Ucc 30V and LM324), but they are not precise enough, since i couldn't get voltage less than 3-4 volts.
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This circuit is not designed for the high voltage you have.

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how i have to connect the Outputs to get +-30V ?

do you have test it ?

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You can't do that with a single supply.

You need to build two supplies and put them in series to make a +/- 30V supply.

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i know ...

i will build 2 Supply

and than how i have to connect the Outputs to get +-30V ?

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This circuit is not designed for the high voltage you have.

I'm aware of that, yes. I guess i'll just make some tests, try to re-design it,  and if it turns out all wrong, i can always put some voltage regulator for regulator part, while pre-regulation will take care of power transistor. I didn't intend to go so high, but i made a mistake when ordering toroid and now i'm stuck with too high voltage, and i don't want to waste 225 VA toroid...

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