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100 amp Variable Voltage Power Supply Circuit

Last Updated on August 21, 2020 by Swagatam 98 Comments

The post describes a  simple but extremely versatile 100 amp, variable voltage power supply circuit using just a few BJTs in parallel and in a common collector mode. The idea was requested by Mr. Andre.

Technical Specifications

Hello Swagatam, I was wondering if you could possibly assist me. on the blogs I have seen some diagrams for simple variable power supplies.

Firstly I know very little about electronics, but with a shopping list and a diagram I am sure I would be okay.

I would like to build a simple variable power supply with an input of 220/240 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A.

I have started zinc electroplating as a hobby (have sweaty hands and want to protect all my tools) the chemical company gave me these as a more or less dependant on my zinc plating bath size.

At the moment the little 6V 8A Ryobi battery charger works for a few minutes, overheats and cuts out till it cools down again. I would really appreciate any assistance you could give me on this.

Many thanks

Andre

The Design

A very straightforward circuit design for the proposed 100 amp variable voltage power supply can be witnessed in the following diagram.

caution electricity can be dangerous

The design basically utilizes a common collector or an emitter follower topology for implementing the operations, by incorporating just a few Darlington power transistors, some resistors and a pot for varying the output voltage.

As can be seen in the diagram, the collectors and the emitters are all joined in common across each other while the bases are made into a common line via individual limiting resistors.

The free ends of these resistors are joined together with a pot across the negative line of the circuit, which determines the voltage regulation at the output of the circuit.

For acquiring more current, more number of transistors may be added in the design, and for reducing the output amps, these may be simply deducted from the configuration.

For inputs above 50V the pot must be upgraded to a high wattage type to sustain the high voltage across its terminals.

All the power devices must be mounted over a common aluminum heatsink without any mica isolation, so that the dissipation is shared uniformly across all the devices and a thermal runaway situation is prevented.

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About Swagatam

Swagatam is an electronic engineer, hobbyist, inventor, schematic/PCB designer, manufacturer. He is also the founder and the author of the website: https://www.homemade-circuits.com/, where he loves sharing his innovative circuit ideas and tutorials.
If you have any circuit related queries, you may interact through comments, and get guaranteed replies from the author.

Reader Interactions

Comments

  1. Naude says

    July 4, 2023

    The circuit is simple and effective
    I have a problem with short circuit protection at 50V output.
    It does not respond fast enough even if I limit the current at 2.5A
    Even a relay current cut off circuit is to slow
    The TIP142 blows instantly
    Any recommendations?
    Regards
    Naude

    Reply
    • Swagatam says

      July 5, 2023

      You can add a current control feature to the above design as shown below. The current control transistor can be a 2N2222. Make sure to add a series 2.2K resistor with the potentiometer. The current limiting resistor RX can be calculated by solving the formula, RX = 0.7 / Max current.

      https://www.homemade-circuits.com/wp-content/uploads/2023/07/100-amp-current-controlled-variable-power-supply.jpg

      Reply
      • Naude says

        July 5, 2023

        Thank you. Will try
        I looks as if with the 2k2 there my output will only be 46V if my input is 56V and I need at least 50V max

        Reply
        • Swagatam says

          July 5, 2023

          OK, in that case put the 2.2k resistor in series with the wiper arm of the pot, just after the arrow head. This is actually to safeguard the 2N2222 current limiting transistor. However I think 2N2222 is rated at a maximum of 40 V, in that case you can use some other NPN transistor which can handle upto 100V.

          Reply
          • Naude says

            July 5, 2023

            Of coarse! I see. Thank you
            I will report back

            Reply
            • Naude says

              August 10, 2023

              Hi
              I had time to test the current limiting today
              Like all the other methods it does limit current what it was designed for but on 50V with a dead short on the output it is just not fast enough and blows the darlington collector emmitor

              Reply
              • Swagatam says

                August 11, 2023

                Hi, maybe the current limiting resistor value was not appropriate, you can try increasing the value of the resistor, that might solve the issue. If not then it is unfortunate.

                Reply
  2. Mahyar says

    May 18, 2023

    I am sorry to say that this is not a good circuit and its construction should not be recommended. Unbalance of collector current of transistors followed by thermal runaway is unavoidable

    Reply
    • Swagatam says

      May 18, 2023

      Emitter resistors are provided to avoid thermal runaway. The circuit may not be efficient but very easy to build and implement.

      Reply
  3. Trevor Daniel says

    March 27, 2023

    I am trying the 100amp power supply and it would not work , is they any one who got it to work

    Reply
    • Swagatam says

      March 27, 2023

      What kind of problem are you facing? Try with 10 amp first and check the response.

      Reply
      • Trevor Daniel says

        March 27, 2023

        I am getting the same input voltage at the output and not adjusting, what I did to get it to work I place the input voltage on the base, and the base resistors on the collector and got a good variable voltage on the emitter but it cannot handle a load, it falls off from 13.8v to about 5v.

        Reply
        • Swagatam says

          March 27, 2023

          If the voltage is not adjusting then something might be be wrong with your transistor or the connections. Try with a small load at the output and check whether it is adjusting or not.

          Reply
  4. Manjunath says

    May 2, 2022

    Hi Swagatam,
    Good day to you. I am Manjunath. I have read your articles and the answers are good. I have a question that is how to convert DC 5Volts 3 Amp from the Battery pack of DC 12Volts 90Amp? Please give me your ideas for me.

    2nd question is how to make a charger (Input AC ~220 Volts) for a Battery pack of DC 12Volts 90Amp.

    Reply
    • Swagatam says

      May 2, 2022

      Thank you Manjunath, for liking my articles.

      You can probably try customizing the following circuit for boosting 5 V to 12V

      https://www.homemade-circuits.com/wp-content/uploads/2021/05/boost-charger-compressed.jpg

      You can adjust the number of turns of the coil to test the output response.

      For the charger you can simply refer to the following article:

      12V Battery Charger Circuits [using LM317, LM338, L200, Transistors]

      Reply
      • Manjunath says

        May 5, 2022

        Hi Swagatam,
        I am asking about the buck converter from 12volts 100 Ah battery to 5v 3A., not for the boost converter. If you have any ideas on it please share them. You are only the person who can help me…Please help me on this.

        Reply
        • Swagatam says

          May 5, 2022

          Hi Manjunath,

          OK for a buck converter circuit you can customize the following circuit according to your own needs:

          PWM Solar Battery Charger Circuit

          If you have any further queries, please let me know.

          Reply
  5. Karan says

    January 6, 2022

    Hi Swagatam,
    I am always inspired from your post as they’re always helpful and great.
    This circuit is interesting i want to test it as i have a SMPS 12v and 100amps. But one thing is confusing. In the given above circuit you used 11 transistor as each can bear 10A so overall 110A safe range for 100A.
    If i connect my SMPS with it and for example voltage is decreased using the pot (given in your design) wouldn’t be the current at the output become high enough to blow transistors immediately.
    I see that the circuit doesn’t have protection against overload and short circuit at the output. Please guide me if anything i can add or modify for it. Many thanks & Hats off always

    Reply
    • Swagatam says

      January 6, 2022

      Hi karan,

      The number of transistors are actually not accurate, for 100 amp current there must be at least 20 nos of TIP142. More the numbers cooler will be the transistors.
      The current through the transistors will depend on the load, not on the voltage adjustments. But yes wider input/output differential will cause the transistors to heat up a lot, that’s the drawback of all linear power supplies. To correct this, the input voltage range from the SMPS must be reduced appropriately.

      Protection has not been provided, you can add a current limiting by adding a common 2N2222 limiting circuit network, as explained in the following concept.

      2 Best Current Limiter Circuits Explained

      Reply
  6. Saqib says

    October 14, 2021

    Hi
    I want to DIY Electroplating IGBT controlled full DC Rectifier 0-30 Volt DC and 500 Amp. Please help me out I saw some readymade circuit on Aliexpress but without full diagram

    Reply
    • Swagatam says

      October 14, 2021

      Hi, sorry, presently I do not have the requested circuit with me…

      Reply
  7. Rafael says

    October 9, 2021

    Hi Swagatam. I am searching a circuit which I can use as battery charger and as welding machine. I mean, by the primary of the transformer regulate the current and voltage. Where I can set up voltage for battery charger and charging current. I I need a welding machine use it with this application. Max voltage 40 or 48 and current from 30 to 1000.
    Is it posible to design?

    Reply
    • Swagatam says

      October 9, 2021

      Hi Rafael, 30 to 1000 amp looks too high, and will require special mosfets to control the current….the transformer primary cannot be used for regulating the current.

      If possible I will try to find a suitable circuit for you soon…

      Reply
  8. mohd mujeebuddin says

    August 21, 2021

    hello sir,
    I need 5 volt dc and 100 amps power supply circuit diagram so please send me as soon as possible and send me your phone phone number for further conversation.
    thanks

    Reply
    • Swagatam says

      August 21, 2021

      Hello Mohd, sorry I do not have a 5V 100 amp smps circuit with me at this moment…

      Reply
  9. Paul says

    August 19, 2021

    how is this circuit going to give 100 amps, when you have 11 resistors in parallel of 3 w each, 10 amps makes more sense, but how is it going to pass 9 amps through a 3ohm resistor and dissipate 3 watts ???????

    Reply
    • Swagatam says

      August 20, 2021

      It is just an idea, you can customize it by reducing the resistor value, or add more number of transistors stage in parallel.

      Reply
  10. Tom Filipcevic says

    May 11, 2021

    Looking for advice regarding a magnetiser I want to build for magnetising tachometer magnets. I would like to utilise the core of a welding transformer to wind a U shape electromagnet of 1500 turns which will carry 8 amps of current at 120V DC. The current will be switched on only for a few seconds at time to produce the magnetising field. I need a circuit for producing the 120V DC from a 240 V 50hz transformer. In that circuit I would like to use an SCR to turn on the current flow and have means of turning it off, either mechanically or electronically. Please advise if this is of interest to you,

    Reply
    • Swagatam says

      May 11, 2021

      You can try implementing the following design

      how to use SCR as a switch

      Reply
  11. Herbert borogha says

    May 2, 2021

    I like to know more about this news letter

    Reply
  12. Ricardo Sanchez says

    April 28, 2021

    I assembled the circuit but the pot is extremely sensitive to any movement. When I connect a 12v motor and I set it to 12VDC output, the voltage drops to just over a volt using 22vdc battery as the supply voltage. Did I assemble incorrectly? I checked all the voltages across the TIP142’s, and all the voltages are almost the same in reference to ground. By the way, the motor works fine just using the battery. I need to make this circuit work so that I can connect multiple devices to a battery set and make sure all the current is drawn through the BMS. Thank you

    Reply
    • Swagatam says

      April 28, 2021

      What is the current of the motor? And how many TIP142 have you used?

      Reply
  13. Ken says

    January 28, 2021

    Hello again Swagatam,

    I’m building a power supply that will be 60v @ 20a. The transformer that I’m using after rectified and a smoothing cap is at 90v. It’s over a 1000va transformer. I want to get it regulated down to 60v. Would this circuit work with just a few TIP142s. I also have some 10k precision pots that are rated for higher voltage, but would probably end up using fixed value resistors. Or would you have a better solution.

    Thanks, Ken

    Reply
    • Swagatam says

      January 28, 2021

      Hello Ken, yes, the above circuit can be used for the mentioned purpose….. for more info regarding the same and all the calculations you can refer to the following post:

      How to Design a Stabilized Bench Power Supply Circuit

      Reply
  14. Dave Bedwell says

    October 25, 2020

    I would like to build a simple variable power supply with an input of 110 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A

    Reply
    • Swagatam says

      October 25, 2020

      You will need an SMPS design for this, however I do not have this circuit with me at this moment

      Reply
  15. George Thomas says

    July 31, 2020

    Hey there,
    I am looking for a 8.1 100A buck converter. The power source is an Hp server power supply as seen here (https://www.ebay.co.uk/itm/HP-Proliant-1000W-Pwr-Supply-DL380-G5-DL385-G5-379124-001-HSTNS-PR01-403781-001/143648658961?hash=item2172209611:g:sw4AAOSwYxBemwUa)

    Would this be possible. This will be used to charge a 3s2p supercapacitor. if possible Constant current and voltage.

    Reply
    • Swagatam says

      August 1, 2020

      Hey, can you provide the input voltage source specifications for the buck converter?

      Reply
      • George says

        August 1, 2020

        It’s 12v max 82A

        Reply
        • Swagatam says

          August 1, 2020

          You can try applying the following concept, but the transistors and the inductor will need to be heavily upgraded to handle 100 amps

          PWM Solar Battery Charger Circuit

          Reply
  16. Reymund says

    July 17, 2020

    hello, i would like to ask if i can use this circuit to regulate the output of a 12v SLA battery to 100amp only? or less lets say 80amp. thanks.

    Reply
    • Swagatam says

      July 17, 2020

      Hi, no, the above circuit will regulate only voltage, not current.

      Reply
    • Reymund says

      July 18, 2020

      do you have any circuit that can regulate sla battery current? thanks

      Reply
      • Swagatam says

        July 18, 2020

        You can use the following concept:

        https://www.homemade-circuits.com/regulated-car-battery-charger-circuit-for-garage-mechanics/

        You can replace the transformer with your battery, the output will produce a voltage and current regulated supply

        Reply
  17. K Premila says

    December 27, 2017

    Dear sir,
    The request is , Quote “I would like to build a simple variable power supply with an input of 220/240 volt ac and an output variable voltage of approx. 1.5V to approx. 15V and a variable output current of up to approx. 100A.” Unquote.

    If you clarify on following points i will be happy. The quote mentioned variable output current of upto 100A .Is the current variable in your circuit or it is fixed 100 A.
    Where the input is to be connected, i think a separate 230 V Ac to 12 V Dc has to be wired separately?
    In the above mentioned circuit, one is 150 A and other 100 A, what is 150A and 100 A. Why both outputs are given

    Reply
    • Swagatam says

      December 28, 2017

      Dear K premila,

      The current is not variable, it will almost equal to the input current supply.

      the circuit is designed to work with a 100/150 amp transformer.

      The output is shown as 100amp to indicate that a minimum 100 amp can be achieved without fail with an input of 150 amp.

      If you want to avoid the transformer, it may be possible by replacing all the BJTs with MJ10023 and by feeding a rectified/filtered 310V at the input side, this design being not isolated from mains this configuration can be dangerous to touch, so proceed with caution

      Reply
      • K.Premila says

        December 28, 2017

        Thanks for your clarification
        Regards
        Premila

        Reply
        • Swagatam says

          December 28, 2017

          you are welcome!

          Reply
  18. joao says

    December 11, 2017

    Ola Swagatam,

    como faço para te enviar um arquivo para analise?

    Reply
  19. joao says

    December 10, 2017

    Olá Swagatam,
    como posso enviar um projeto para analise?

    Reply
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