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0-30 Vdc Stabilized Power Supply

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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

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

So Finally which version of schematic is correct  / flawless  to  build the PSU ? 

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  • 2 weeks later...
  • 2 weeks later...

Hello All,

I am currently looking for the components to put this project together. It seems that the Op Amp TL081 is not so easy to find in my area.

National Semiconductor says that the TL081 can be used to upgrade circuits which use the LM741. Also that the LF411 can be used as a substitute for the TL081.

The LM741 is available locally. Can I use thise as a substitute?

Thanks for your replies.


Project Link: http://www.electronics-lab.com/projects/power/003/index.html

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Copy-paste from TL081 datasheet:

"The TL081 is pin compatible with the standard LM741 and uses the same offset voltage adjustment circuitry. This feature allows designers to immediately upgrade the overall performance of existing LM741 designs."

Replacing TL081 with LM741 may drop the overall performance and quality of the power supply, but it will work as they are compatible. Otherwise TL081 is a very common opamp, so try to search it a little more.. it worths to do it.

Don't forget to send feedback when you build it!

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Thanks again. So, I will begin to source the components and begin to build the unit. This will take time (as everything when one has many things to do). I will let you know my experiences.

I am thinking that the PN2219 is the same as the 2N2219, only with a different package, so I have a few things to try.


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  • 2 weeks later...


I like your web site.
I'm interrested about 0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A and have couple of questions.
Is it possible to increase output current to 5 Amps ? (adding 2N3055 and changinging some component values)
Can I built 2 similary power supply and use it in serial mode 0-60 V or in parallel mode to get more current 0-10 Amps or use it like dual power supply +/-
30 V ?

Thank you



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I have built the 0-30 VDC STABILIZED POWER SUPPLY & 3 amps Power Supply, put in a voltmeter and an ampmeter and a power LED. I found this power supply very useful and like the design very much.

I wish I could increase the max. current from 3 AMPs to 5 AMPs e.g. by changing the transformer, diodes and Transisters and PCB tracks width and heat sink etc.

Anyone with good suggestions?

Alternatively, is there a good switch mode PS circuit with variable voltage and variable curent limit that has max current 5 Amps or more?


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  • 2 weeks later...

I'm beginning to wonder if this is a little too much for my first project but I'm learning lots!

On the Parts List, item:

D1, D2, D3, D4 = 1N5402,3,4 diode 2A - RAX GI837U

...has me a little confused. This means the bridge would be four 1N5402's OR four 1N5403's, etc. and not one diode of each part number, right?

What is "diode 2A - RAX GI837U"? Is it a diode (which I'm not able to find any info on)?

I would like to make some small changes and play with it before I build it. By chance, has anyone tried to setup this schematic in Tina for Windows, Student Version? Any problems doing this? I'm having problems but suspect it's most likely user issues. ::)


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Right, you use the same 4 diodes to build the bridge.

Here is the datasheet of 1N54XX: http://www.onsemi.com/pub/Collateral/1N5400-D.PDF

The 2A diode means that the diode must be 2A or more. The 1N54XX are 3A so it's ideal to use them. Also the RAX GI837U is an alternative diode or bridge rectifier that seems to be hard to find it.

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Today i received a report from a user from Argentina that build this power supply and it worked in his first attempt.

Also he made the following modifications:

"Replace R2 and R3 with 1/2W resitors, R2 heater, R7 with 10W resistor and R1 with 2-3W, C1 for 4700 uf, P1 is a many-turns wire-potentiometer (10 turns), and P2 is a "cermet" single-turn."

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I also have a few sugestions for this circuit, but also a warning. First i sugest that you bypass the diodes D1 to D4 with a couple oh caps, about 1nF to 4.7 nF, soldered directly over the diodes. Also bypass diode D7 with a cap, lets say 10 MFD to 47 MFD. The supply to the IC:s should also be bypassed with a ceramic cap, about 100 nF. And so the warning, how about the SOA(Safe Operating Area) of the output pass transistor Q4?


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  • 3 weeks later...

I think I understand how to add a voltmeter to this project though, I've been wrong before! It's the current part I'm a little confused about.

An ammeter wouldn't show any reading until the power supply was connected to a load, right? So, can a meter (ammeter?) be added to this project to show where the current limiter is set?

Should I add a couple of connection points to the pcb diagram to do this and if so, where?

Thanks again!

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You will find a good Digital LED Voltmeter here :


It uses 7107 and can easily converted to a Digital Ammeter. Below i attach the basic connection diagramm with the connections as a voltmeter and as a ammeter.

Also read this: http://www.electronics-lab.com/forum/attachments/Digital_Panel_Meter.pdf

It's true that you need to connect a load to the output. Read this to understund how to current limiter works.

Current Limiter Function

Another very important feature of the circuit, is the possibility to preset the maximum output current which can be drawn from the p.s.u., effectively converting it from a constant voltage source to a constant current one. To make this possible the circuit detects the voltage drop across a resistor (R7) which is connected in series with the load. The IC responsible for this function of the circuit is U3. The inverting input of U3 is biased at 0 V via R21. At the same time the non inverting input of the same IC can be adjusted to any voltage by means of P2. Let us assume that for a given output of several volts, P2 is set so that the input of the IC is kept at 1 V. If the load is increased the output voltage will be kept constant by the voltage amplifier section of the circuit and the presence of R7 in series with the output will have a negligible effect because of its low value and because of its location outside the feedback loop of the voltage control circuit. While the load is kept constant and the output voltage is not changed the circuit is stable. If the load is increased so that the voltage drop across R7 is greater than 1 V, IC3 is forced into action and the circuit is shifted into the constant current mode. The output of U3 is coupled to the non inverting input of U2 by D9. U2 is responsible for the voltage control and as U3 is coupled to its input the latter can effectively override its function. What happens is that the voltage across R7 is monitored and is not allowed to increase above the preset value (1 V in our example) by reducing the output voltage of the circuit. This is in effect a means of maintaining the output current constant and is so accurate that it is possible to preset the current limit to as low as 2 mA. The capacitor C8 is there to increase the stability of the circuit. Q3 is used to drive the LED whenever the current limiter is activated in order to provide a visual indication of the limiters operation.

As you understund you can measure the "preset voltage value" adjusted by P2 and convert that value to the corresponting current limit set point in a way.

Hope that drives you to the right direction.

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In order to connect a Voltmeter and Ammeter to the Power Supply, I need a +5V power source.

I am thinking of building a secondary power supply that takes a 24V DC current from the main 220/24 V 3A transformer + Rectifier, in other words connect another power supply to the output of the diode bridge of the main power supply.

My question is what components I have to use in order to build this simple power supply. I read the article by Kyriakos Kontakos "5V / 1A Power Supply" and I found out that I need two electrolytic capacitors, two simple capacitors and a regulator.

I suspect that I need the following components :

C1 2200 uF/35V
C2 100 nF
C3 100 uF/16 V
C4 100 nF

and one LM7805. I think the capacitors are suitable for 24V DC input and 5V DC output. But is the LM7805 suitable of taking 24V DC for input ? Does it need a cooler for it ? The difference between 5V and 24 V is somehow large.

And something more, could someone explain to me the role of those four capacitors ?? Thanks !!!! :D

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  • 2 weeks later...

Billy: The regulator might get hot with this amount of difference, so you should add a heat sink. Also, in regards to the capacitors, when you add a capacitor to the input side of the regulator, isn't there already one there for the other part of the power supply? When you put two capacitors in parallel on the same line, it changes the value of capacitance and will actually cause less filtering in many cases. Check your values with the capacitor parallel formula (Ctotal= (1/(1/C1+1/C2+...1/Cn))). You will probably not want the additional one there. Be sure that all capacitors are well above the max voltage range. I usually use the times2 rule when possible, but this is not necessary. This is only my own personal safeguard.

Firefly: You should not need additional transformers to run a fan or meters. If your existing transformer is capable of the added current usage, you can tap into it just after the rectifier bridge with a regulator or a zener/resistor for the correct voltage drop.

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Hello All,

Seems we are all making our modifications to this project. I hope someone can help me with mine.

I would like to use two variable resistors each for the adjustment of voltage and current to enable coarse and fine adjustment.

The circuit calls for 100k variable resistors. Is it possible someway to wire in 10k variable resistors for the fine adjustment?

How does one wire the 100k and 10k variable resistors together?

Thanks for any help. A diagram would be great.

DerFly. ???

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Thanks MP. This site has an LCD panel meter that seems cheap enough:


Not sure about the quality. Any thoughts on that?

The description states: "Note: Supply voltage must be independent of voltage being measured." I've seen something similar for some other meters.

Any idea what that is about? Would this meter need a separate transformer or would it be good enough if it was on its own taps?


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Firefly, they are just trying to say the supply voltage must be a fixed voltage. The other input is the measured voltage and this is what will be displayed. In other words, you would want to add a 9 volt regulator right after the rectifier bridge to supply this unit and the measured variable voltage will go into a different pin on this meter to display the output voltage of your PSU.

Here is a link to the one I have just purchased. Much better price. In fact, I have not seen one for less. It has different jumpers for decimal point on voltage ranges. 0-2mV, 0-20V, 0-200V, (up to 500V range, I think).



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