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0-30 Vdc Stabilized Power Supply


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I decide to build this project. Only bad thing is, that I saw this topic after buying all parts.
After gr8 disappointment, I'll try to build it as good as I can. I draw something between old and new schematic.
Please tell me what you think and how can I make it better without changing OPamp.
I need about 20V DC output, and around 2,5 Amps for my testings.

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The original circuit should work fine up to 15V at 1A if you replace the old opamps with the newer higher voltage ones. You probably should recalculate the resistors that set the maximum voltage and c

Hi, as promised I made an English translation of my working. Maybe there is few mistakes and I am sorry for that ! Good reading. ExplicationEN.pdf

February 23 above on this page has the latest schematic of the revised 3A lab power supply.

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I'm in the process of deciding on a design for a lab power supply, and this one seems to fit the needs that I have.  However, I have been reading some of the forum replies and I have a question.  Why are you guys using OP amps that aren't rail to rail?  If you used a rail to rail amp, it would eliminate the need for the charge pump negative voltage generator and make life a whole lot easier.  Am I just missing something, or is there a reason for using non-rail to rail OP amps?

Thanks,

Dan

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Please tell me what you think and how can I make it better without changing OPamp.
I need about 20V DC output, and around 2,5 Amps for my testings.


Like the original project, the values for R4 and R10 are wrong and R10 connects to the wrong voltage.
Also like the original project, the main filter capacitors are much too small.
Each 2N3055 output transistor needs a series emitter resistor for matching.
The value of R14 will need to be changed to match your reduced supply voltage.
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I'm in the process of deciding on a design for a lab power supply, and this one seems to fit the needs that I have.  However, I have been reading some of the forum replies and I have a question.  Why are you guys using OP amps that aren't rail to rail?  If you used a rail to rail amp, it would eliminate the need for the charge pump negative voltage generator and make life a whole lot easier.  Am I just missing something, or is there a reason for using non-rail to rail OP amps?

Thanks,

Dan

The latest modifications use easy-to-find MC34071 or TLE2141 opamps that have inputs and outputs that work at 0V with a single polarity supply. Their max allowed supply is 44V. But a low voltage negative supply is needed because the output of U3 must go negative enough (about -0.7V) to allow D9 to force the output of the project to 0V when the output is shorted.
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Like the original project, the values for R4 and R10 are wrong and R10 connects to the wrong voltage.
Also like the original project, the main filter capacitors are much too small.
Each 2N3055 output transistor needs a series emitter resistor for matching.
The value of R14 will need to be changed to match your reduced supply voltage.


Can you suggest values for those components (main filter capacitors and R14)?

Is this mod OK? Do you think it will be good enough for 20V 2A?

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Can you suggest values for those components (main filter capacitors and R14)?

The main filter capacitor should be about 10,000uf.
R10 must connect to the negative supply, not to 0V.
R14 should be 1.8k with your 22VAC transformer.

Is this mod OK? Do you think it will be good enough for 20V 2A?

One 2N3055 transistor could be used if it has a pretty big heatsink.
With two 2N3055 transistors the circuit will supply 20V at 2A perfectly.
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With a 20,000uf capacitor you should use a 10A rectifier bridge module.
The circuit will overload your transformer because its max current will be about 4.1A.
Use 1 ohm for R7 for about 2A max.

Many of the resistors in the original project got too hot. You will need to calculate the dissipation of them to see if they should be bigger.

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But a low voltage negative supply is needed because the output of U3 must go negative enough (about -0.7V) to allow D9 to force the output of the project to 0V when the output is shorted.


Ahhhhhh that makes sense.  I was wondering how that all worked, but now its clear.  Thanks!

I'm in the process of scrounging up parts for this (I would like to make a dual rail one for +/- supply needs).  Hopefully it all goes well.

-Dan
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Hello everybody. i have a question about the final version of this psu, i can see that there are 2 trimmers, the ones around the op amps with the resistors in series, i just wondered what they do and how do i adjust them?
thanks

One trimmer adjusts for exactly 0V.
One trimmer adjusts for exactly +30.0V.
One trimmer adjusts for exactly 3.0A.
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Thanks audioguru, but.. wich one does what and at wich point i measure this.

Measure the output voltage with the voltage setting pot turned down and adjust the input offset adjustment trimmer on U2 for exactly 0V.

Measure the output voltage with the voltage setting pot turned up and adjust the gain trimpot for U2 for exactly +30.0V.

Connect a load for more than 3.0A.
Measure the output current with the voltage setting pot turned up and the current setting pot turned up and set the trimpot near U3 for exactly 3.0A.

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Hey Guys!

It seems to be a view gurus here and I hope someone is able to help me!
I bought the whole parts which are needed for the second project shown in the schematic. I have simulated the schematic and now I am not sure if some parts will be damaged.

I used a 30V 230VA Transformer with max. 3.83A. My first Problem - the voltage of the transformer without load will be 32.47V.
32.47V*sqrt(2)=45.9V  :o
Is this to much for the MC34072? Maybe I can use a smaller value for R1 to hold the transformer-voltage small?

And the second question is shown in the simulation file of I_C1. The current through the capacitor by 3A output will have peaks up to 6.5A. The fuse will be "4A slow" and the transformers max. current is 3.83A. The same problem in the first view milliseconds.

Will the transformer or the oamps be damaged? And if it will be - what should I do because the transformer and C1 are very expensive!!!

Thanks for your help!!!
Markus

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I used a 30V 230VA Transformer with max. 3.83A.

One of the  numbers is wrong. 30VAC at 230VA is a current of 7.67A, not just 3.83A which is too small.
The transformer must be rated for 130VA or 4.3A.

the voltage of the transformer without load will be 32.47V.
32.47V*sqrt(2)=45.9V  :o
Is this to much for the MC34072?

The 30V/130VA/4.3A recommended transformer has a voltage of 31V without a load. Then its peak voltage is 43.8V and the rectifiers (yours are way too small) reduces the positive unregulated supply to 42.4V which is less than the max allowed supply for the MC34072 opamps.
But you cannot use the MC34072 dual opamp because each opamp has a different supply voltage.
Instead you must use MC34071 single opamps.

Maybe I can use a smaller value for R1 to hold the transformer-voltage small?

It will waste most of the transformer's power and will be huge and hot.

And the second question is shown in the simulation file of I_C1. The current through the capacitor by 3A output will have peaks up to 6.5A. The fuse will be "4A slow" and the transformers max. current is 3.83A. The same problem in the first view milliseconds.

The capacitor is designed for very high peak current as a power supply filter so it will be fine.
The transformer takes a long time to over-heat but the high current pulses are a short duration.
I think the current pulses will be higher current which is fine.
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Hi!

Thank you for your fast answer!

I can put your mind at rest - the rectifiere-diodes are for simulation only  8)
I have found a diagram for the Fuse - it will not be blown by the current  :)
I haven't found a MC34071 so I decided to use 3xMC34072. But thanks for the advice!

The transformers data are correct - it has two secondary windings with 30V means 2x30V with 3.83A=230VA.
The second winding will be for a second power supply if the first works.  ;)

But now I still have the Problem with the transformer:
Without load it has 32.47V*sqrt(2)=45.9V minus 1.2V from the 10A Bridge Rectifiere = 44.7V!
The Simulation shows that the voltage is increasing slowly to about 45V (don't know why  :-[ I don't care...)

It's close... I have no experience with oamps and too much supply voltage but could it be possible to work with them
or are there any other oamps I can use?
Maybe a "OPA 551PA"?
Datasheet: https://www.distrelec.com/distrelec/datasheets.nsf/WebAttachments/F11F0007492D7988C12570E90019A751/$File/641297.pdf

Thanks! Markus

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What do you think about NE5534AN? It's the most similar to MC34071 that I could find in my country!
I'm thinking about building new circuit.  ;D

The MC34071 and TLE2141 opamps have inputs that work at the negative supply voltage and have outputs that go down to the negative supply voltage. Most opamps including the NE5534 have inputs that do not work if they are 2V or less away from the negative supply voltage and have outputs that go only 2V away from the negative supply voltage.

So the NE5534 opamp could be used if it has a -5.6V negative supply and if the transformer voltage is reduced (which will reduce the max output voltage of the project.
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Hello!

I read most of the new post over the latest PS. I have at home only 24VAC transformec which i want to use with the latest schematics of the PS. So like i read on the forum that my transformer will be not good to get 30V output.
I am asking now if it is possible to change the schematics to get output with the TLE2141 opamp and 24VAC/6A transformer 30V?

P.S.
Here is my schematic which i tested and i noticed that is no effect on minimum and maximum output with the the last two trimmers. I only get 23V max and 0.112V min.

Thank you in advance for helping

P.S.S.
Sory for my bad english:(

Napajalnik_30V_5A_circuit.pdf

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I have at home only 24VAC transformer which i want to use with the latest schematics of the PS. So like i read on the forum that my transformer will be not good to get 30V output.
I am asking now if it is possible to change the schematics to get output with the TLE2141 opamp and 24VAC/6A transformer 30V?

No.
The peak voltage of the 24VAC transformer is 33.9V and the rectifiers drop it to 31.9V. The main filter capacitor has ripple that reduces the unregulated positive supply to +29VDC.
At 3A, R7 has a voltage drop of 1.41V, the 2N3055 transistors and their emitter resistors have a voltage drop of 1.5V and the BD139 has a voltage drop of 1V. Opamp U2 has a voltage drop of 1.2V.

So the 29V unregulated supply has a total loss of 5.1V to 23.9V and could be lower if your transistors are slightly weak or if your mains AC voltage is low.

The TLEC2141 for U2 has a max input offset of only 1.5mV when it is warm. Its gain is 3 so its max total input offset voltage is only 4.5mV. The offset voltage adjustment trimpot should be able to null the output voltage to zero if the voltage-setting pot gives zero volts output.
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Hello!

Thanks for answering, so as i understand you it is not possible do with this opamp. So if i want do this i must build the first version of power supply which ,as i read on the forum, is not so good and try it if it works for me  or is it possible just to find another opamp?

Please advise me what to do if it is any solution ?

Thank you in advance
Bye

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