0 to 50V, 0 to 10amp Variable Dual Power Supply

The post explains a simple yet very useful 0 to 50V dual power supply circuit which also includes a wide range current control feature right from 0 to 10 amps. The idea was requested by Mr. Tamam.

Technical Specifications

It was my long term dream to build a 2 channel power supply for personal use, I have seen a lot of circuits, but those does not fit my criteria.
However, please take a look at the following requirements and let me know if its possible or not, if possible I will be the happiest person in the world.

1. Output voltage range: -50V to 0V to +50V ( must be adjustable by individual channel )

2. Output Current range: 0A to 10A  ( must be adjustable by individual channel )

3. Output would be Duel channel, means total 6 outputs,

Channel 1 (Positive, GND, Negative)     Channel 2 (Positive, GND, Negative)

4. Power Supply Unit should contains 2 Voltmeters and 2 Ammeters (Analogue) for 2 individual channel.

5. Power Supply Unit must have short circuit protection and cooling fan featured and extreme heat protection.

6. I don't want to use any PIC or AVR, so please avoid those.

Money is not a matter here, I will spend continuously until above requirement meets.
Even If I need any custom transformer I will order and make it from our local area.
I have seen many ready made power supply in market but I want to make it by own hand. You just show me the way... please bro, I will be pleased to you for lifetime.

Thank you very much !!

Best Regards,


 Circuit Diagram




The Design

The basic design of the proposed 0 to 50V variable dual power supply circuit with 0 to 10 amp variable current facility is shown in the above figure.

The entire design is transistor (BJT) based and is virtually indestructible. Moreover it's equipped with an over load and over current protection features.

The two section included in the design are exactly similar with  their configurations, the only difference being the use of PNP devices in the lower configuration while NPN in the upper configuration.

The upper NPN design is configured to produce a variable response right from 0.6V to 50V positive while the lower PNP section becomes responsible of producing an oppositely identical response from -0.6V to -50V output.

The Transformer Specs

The maximum limit could be suitably changed simply by changing the voltage rating of the transformer. However for higher voltages you may have to appropriately upgrade the BJT voltage ratings accordingly.

In both the designs, P2 executes the function of varying the voltage levels as desired by the user, while P1 functions as the current regulator and is used for adjusting or setting the output anywhere from 0 to 10 amp current. Here too the maximum rating depends on the selection of the transformer amp rating and may be changed as per individual preferences.

T1s in the both the sections become the fundamental part or the heart of the entire voltage control functioning in the circuit, which becomes possible due to the popular common collector configuration of the devices.

The other two active BJTs only help to implement the same just by controlling the base power of the T1s thus making it possible to adjust the thresholds to any desired user defined voltage and current levels, as per the ratings of the transformer or the input supply.

Parts list

R1 = 1K, 5 watt wire wound

R2 = 120 Ohms,

R3 = 330 Ohms,

R4 = to be calculated using Ohms law, R = 0.6/Maximum Current Limit, Wattage = 0.6 x Maximum Current Limit

R5 = 1K5,

R6 = 5K6,

R7 = 56 Ohms,

R8 = 2K2,

P1,P2 = 2k5 presets

T1 = 2N6284 + 2N2222(NPN), 2N6286 + 2N2907(PNP)

T2, T3 = BC547B (NPN) BC557B (PNP),D1, D2, D3, D4 = 6A4,

D5 = 1N4007,C1, C2 = 10000uF/100V,

Tr1 = 0 – 40 Volts, 10 Amp

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Muhammad Hamid said…
Dear Swagatam,You have connected C3 in reverse order in above circuit.It will charge in reverse polarity which will damage the capacitor.C3 positive terminal should be grounded while the negative terminal should be at negative voltage.Thanks
Swagatam said…
Dear Muhammad, thanks!

yes the lower caps were wrongly polarized, I have corrected the diagram now, please check it.
Hi,what rating of transformer did you use here? I mean the voltage and its current rating. Thanks!
Just to add to my question, what pnp transistors should I use to the lower ciruit?
Swagatam said…
It can be a 50-0-50V 10amp trafo.
Swagatam said…
MJ2955 for the PNP and 2N3055 for the NPN

and BC556 for the PNP and BC546 for the NPN
Will a transformer with a lower current and voltage rating still for this circuit say 24-0-24, 3amp? If so, are there modifications that I have to do like have to change vlaues of some resistors or change a transistor etc? Thanks!
Swagatam said…
any voltage and current can be used with this design, depending upon the maximum tolerable rating of the transistors.......no modifications would be required
Dear Swagatam,
Can you recommend a short-circuit protection for this circuit?

Swagatam said…
Dear Ramunas, the above design is already short circuit and overload protected.
gowhar khan said…
Dear Swagatam

MJlorton has added a link of your variable circuit diagram uploaded on brighthubengineering.com in his video series of how to build a variable power supply and i feel proud of looking at it. i am in search of a versatile digital variable power supply diagram with the specifications of 0-30v 0-5amp. i shall be highly obliged if you could provide me the same either existing diagram with required modification or you are requested which decent brand of variable bench power supply should i get for hobby electronics and laptop repairing. Thanks a lot
Swagatam said…
Dear Gowhar,

you can probably try the following design, this looks exactly suitable as per your required specs:

Dear Swagatam,

I can use SC1815 and SA1015?

Swagatam said…
for which transistors do you want to use these?
Swagatam said…
If both are NPN and rated at 60V (collector V) then you can use it
chavda jaydip said…
Hi swagatam sir
I need 12v-3amp power supply for my project
so please help me.
Swagatam said…
Hi jaydip, you can use an IC LM338 circuit for your requirement.
Hi sir, why there is so many pots in above circuit.Can you tell me the fuction of that 4 pots?, for example (pots 1 for adjusting voltages).And i want to use 24v 10 amp trafo for this, will this work?thanks sir
One more question sir, can i use same transistor for both upper and lower circuit?(i use 2n3055 for npn and mj2955 for pnp)thanks sir
Swagatam said…
Hi Raihan, the upper positive section has two pots one for voltage adjustment and the ohter for current adjustment...the same is true for the lower two pots, which are used for the negative section of the power supply.
Swagatam said…
yes the mentioned transistors will do.
gk adanama said…
Nice diagram... dear swagatam can u please put the diagram which is if i want to put digital volt and amp meter. Thanks before
Swagatam said…
Thanks GK, you can attach the ammeter in series with the positive output terminal of the circuit and voltmeter right across the +/- terminals of the output
gk adanama said…
thank you, but i cant see any pot, trimpot or vr to adjust the voltage and ampere,, how to adjust voltage and ampere on this circuit ?? maybe you can update the circuit coz im still learning how to build adjustable V and A symetrical ps with volt and amp meter. also i cant find where is the Tr1 on this diagram https://homemade-circuits.com/2012/01/how-to-make-versatile-variable-voltage.html as shown on the part list.
gk adanama said…
owh sorry my bad, coz u draw the pot just like regular resistor. ok i get it.
Swagatam said…
yes the one which are configured with arrows are the pots....
Swagatam said…
TR1 is the transformer
If I use a 0-36 V 3 Amp transformer for this circuit will the output still be 0-50 V and 0-10 Amp? I really need your reply sir its for our project thank you
Swagatam said…
That's impossible, in fact you will find a little less than 36V and less than 3 amp at the output
then what should i do sir to make an output of 0-50V and 0-10Amp? here in our town there is no 0-40V transformer sir.I hope you could help me sir . thank you
DARWIN said…
sir may i ask . if i use a 33.5V 10amp transformer what should i add to the circuit to make an output off 50V? here in our town we really cant find a 0-40V transformer. I'm hoping for your reply sir thank you
Martyn Lawson said…
Dear sir, Many thanks for this interesting circuit. I see that R4 is to be calculated by ohms law. Could you give me some idea of the calculation here? For example, where is the voltage and current being measured from and this what figures would go into the calculation? Sorry if this is a silly question, but I'm trying to understand how you would determine the value of R4 in any particular case (ie using a variety of transformer voltages).
Many thanks in advance.
Swagatam said…
Thank you Martin, R4 can be calculated in the following manner

R4 = 0.7/max current limit

The value will cause the required triggering voltage at the base of the associated PNP, sufficient to force T1 OFF...this will happen whenever the max current limit is reached or whenever the load tries to draw a current higher than the set limit...it is not dependent on the transformer rather on the load
Martyn Lawson said…
Many thanks Swagatam. That's a very helpful explanation of what is happening.
Best wishes.
Swagatam said…
You are welcome Martyn!!
Mohammad Muwafi said…
Please help me
I want the maximum current 10A
what r4 must i use?
Swagatam said…
R4 = 0.7/10 = 0.07 ohms, 10 watts

use 0.1 ohms/ 2 watt and 0.22 ohms/2 watt resistors in parallel
Sarvesh Kumar said…
Sir may you please tell me the watt of all resistors used here and also types of capacitors ??????
Sarvesh Kumar said…
sir may u tell me watt of all resistors and types of capacitors used here??
Swagatam said…
All are 1/4 watt except R4.

R4 watt = 0.6 x maximum current selected for the output
Swagatam said…
all caps are electrolytic
herr doctor said…
which one is r6 and which one is r8? please clarify these. thanks
herr doctor said…
herr doctor said…
Swagatam said…
I have updated the formula in the parts list
Wandows said…
Hello everyone...
I am very anxious to make this beautiful source.
Would anyone have the layout (pcb) to make available?
I still do not have enough skill to do the layout (I still get there).
Thank you very much!!!
Swagatam said…
sorry PCB layout is not available, however it does not require one since it can be easily built on a general purpose board, with some patience.
kaleem Ashraf said…
Dear Sir
help me
(2N6284 and 2N6286)plz tell me the Equivalent transistors,because for schematic circuit in proteus it will creat a problem,both r not in the proteus library
Swagatam said…
Dear Kaleem, you can make an equivalent by using a 2N3055 and a 2N2222 pair in the Darlington mode for the NPN....

and 2N2955 with 2N2907 for the PNP side
Laura V said…
Dear Sir
My transformer is dual 42VAC and I am trying to get dual 50VDC out of this regulator. Is T1 the transistor which needs cooling? What size You suppose the heatsink should be?
Swagatam said…
Hi Laura, it's possible with proper rectification through a very large C1.

yes definitely T1 will require a large heatsink for optimal functioning. make as large as feasible, or simply by checking how hot it gets...
Dear Mr. Swagatam!
I made circuits same your schematic. But it isn't stability, when transistor T2 is hot, the voltage will down. I assembled heatsink but always need to blow by fan to trans T2 and cooling it. When i use a load, about 20 Ohm, the voltage is down 7-8V with adjust to 40V. My tranformer is 48V. And how I do for Voltage is not change by T2 and load?
Thank you so much!
Swagatam said…
Dear Thanh, if your T2 is getting hot, you can try a higher rated transistor in place of T2, you can replace it with a 8050/8550 pair or a 2N2222/2N2907 pair....to increase the output current you can reduce R1 to 470 ohms 5 watts and see the response.
Unknown said…
Sir my transformer was 48v 3amp. which number for using in r4 resistor
Swagatam said…
It will depend on how much maximum current you prefer at the output.....if it's full 3 amp then you can simply short circuit R4
You'll need to connect a boost converter prior to the transformer, that takes the input from the transformer and boosts the voltage for the input of the circuit above.
Swagatam said…
using a bridge rectifier and a capacitor will step the voltage to above 40V
I can't find R6 in the diagram. Please Help
Where did you use D5? Sorry for asking again and again.
Swagatam said…
beside C2, it's mistakenly printed as D1
Swagatam said…
If you are having difficulty in understanding these simple things, then I think you must first learn all the basics and only then attempt building any circuit
Unknown said…
Can I use tip 147?
Swagatam said…
Where? is it for the PNP power transistor? Darlinton might not work correctly...
herr doctor said…
if you have a few free minutes and you can tell us all about the variable resistors for voltage and current that will be awesome, i mean to which side the pot of voltage will give 0 volts or max volts and the same with the pot of current control, to which side it will give the max current and 0 amps, i hope is not too much to ask, thank you very much.
Swagatam said…
Downward side for P2, and right side for P1 will produce higher voltage and higher current respectively.
hi i want to know what happens when replace r4 with wire (short Circuit the r4)
and can i use a mosfet insted of using npn
Swagatam said…
Hi, if you remove R4, it will disable the current control feature, and the T4 section will become ineffective.
Swagatam said…
...sorry not by removing R4, rather by shorting it, as you mentioned..
Swagatam said…
not sure how a mosfet would respond because minimum switching voltage of mosfet is 6V while for a BJT it is 0.7V...but there's no harm in trying it.
thank you for answering but i made the circuit and then i tried to connect something it didn't give me 1 Amp and when i connected +1.5 Amps to circuit something went burn ,the room filled with smoke.but now i noticed something : you can see the +50v out and isn't connected directly to 2N6284(NPN) transistor it is connected to BC547B which is giving only 100mA and some resistors it will not give more than 100mA with 50v (i tried making circuit for 3 times and it is not working correctly) i hope you correct the circuit i need it, it is awesome thing to have 0v - +50v , 0v - -50v , 0a - 10a power supply i wish i can make it and work correctly and thank you
Swagatam said…
I rechecked the diagram and I could not find anything wrong in it..everything looks absolutely correct.

Make sure that your power transistors are original and duplicate ones, because a few other readers had also failed with this circuit and later they discovered that their main power transistor was faulty originally.

I have already build the above circuit (the NPN section) and used it for more 5 years without any issues...it is virtually indestructible.

the only issue being the power BJT gets significantly hot at full loads.

I think you should go stagewise, first try and build the NPN section successfully, if everything goes correctly after that you can go for the PNP section.

The NPN section is explained exclusively in the following article:


ok i'll try it again and make sure that the transistors are original ones thanks
herr doctor said…
thanks for the data of the potentiometers, that will be helpful for the start up of the power supply at 0v and 0amps, great, hands to work now. thanks again
Swagatam said…
You are most welcome herr doctor...
Richard Collin said…
Hi, why you have choosen for C1 50v instead 63V, the output of the diode bridge is around 54v , for a 0-40V sinewave for tr1.
Swag said…
Hi thanks, I have changed it to 100V...you can refer to the corrected parts list.
Dinu said…
Hi . can I used R4 instead of Variable resistor
Swag said…
Hi, R4 is a fixed a resistor...you can use P1 for varying current...

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