0-30V Stabilized Power Supply

[nand1]

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

 

[audioguru2]

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.

 

[carlos206]

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

 

[audioguru2]

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 LCDView attachment 40663

 

[protoncek]

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)?

 

[audioguru2]

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.

 

[protoncek]

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

 

[nand1]

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

 

[audioguru2]

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.

 

[audioguru2]

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.

 

[protoncek]

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.

 

[audioguru2]

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

 

[nand1]

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

do you have test it ?

 

[Hero999]

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.

 

[nand1]

i know ...

i will build 2 Supply

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

 

[protoncek]

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...

Thanks for your help!

 

[Hero999]

i know ...

i will build 2 Supply

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

Connect the two power supplies in series and use the point where the two supplies are joined as the 0V point.

 

[nand1]

+    +-      - ??

or

+      - -      + ?

thx !

 

[tjaartk]

Hi all

First time for me on this site. I have built this and it works grate. By the way very new to electronics, I have started it as n hobby at 34 (last year). I want to built the two vertions off the amp/volt meters the show with the project. where can i find the scematics and so on for the bords shown and could some one please tell me in laymens terms how the second lcd display one works.  Would epreciate it.

 

[tjaartk]

PS the boards shown of Sam Carmel & and the other one of (programable IC?)