13.8 Volt 20 A Transformerless Power Supply

Transformerless Power Supply circuit diagram

Do you need high current power supply without heavy and expensive transformer? Then, this circuit would be great choice for you.

This 13.8 Volt 20 A regulated transformerless power supply. 20A transformer is very-very expensive, large in size and very heavy in weight.

This power supply capable in delivers around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. Let us see what we have got here. The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation. The rectified current will be ironed by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend up to 50.000uF. This capacity can be built up by several smaller capacitors in parallel. The base of this design is a simple 12V regulator IC 7812.

More explanation about this circuit, please visit this page

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12 thoughts on “13.8 Volt 20 A Transformerless Power Supply

  1. Anindya

    Plaese let me know what is the input current value/range of this circuit so that it will give 20amp o/p current…
    Input voltage value already mentioned in heading but not input current…

  2. circuit diagram Post author

    i’ve check the PCB. C3 on PCB layout should be C4 on the diagram. While C2 on PCB layout should be C3 on the diagram. You need to add C2 on the PCB layout by yourself (refer to the diagram).

    C1 is a ordinary electrolytic capacitor (ELCO). Based on the PCB, the will 3x elco of paralled 13300uF / 33-63V.

    The RL will be 10 x 0.3 ohm resistor with parallel connection. It will resulting 0.03 ohm right..?

  3. Pol-P

    I’m trying to locate the position of C4 in the PCB but unfortunately it’s not included, where is it? What is the exact value of C1? Is it ceramic, tantalum, or if it’s electrolytic, what is the voltage required? What is the exact value of RL? very confusing, (0,03R and 0R3) what is that value?

  4. Ryan B.

    If this is transformerless, why do we need a 25a 17.5v transformer? If we have a 25a available for the required input, we don’t need this circuit, since it’s only 20a at the output.

  5. ryan B.

    If this is transformerless why do we have to use 25A 17.5v transformer? If you use 25A input power naturally the output would be parallel. It means we don’t need this circuit, since we have already 25A power available at the input.

  6. jayddep gajipara

    hi sir
    sir i request u that we want to say how to convert three phase to single phase 30 mA power supply from three phase without neutral and transformer plz give me idea for 440 volt without occurring fault

  7. jomish k j

    Hai, thank you for your circuit,but one thing that without a transformer it can not be used in india.Why because i have a power supply of 230v and 430v.

  8. satya

    This circuit is not a transformerless circuit diagram.
    But this is regulater for 19 v transformer .I just want to say if you can provide a smps circuit diagrame than that would be helpfull instead of this.

  9. Francesco

    just a comment: this circuit is transformerless in the sense that it doesn’t clearly shows the transformer symbol but you will still need a “very-very expensive, large in size and very heavy in weight” transformer to derive the 19.5 DC volts 20A supply that is the input of this circuit…

  10. Mathew

    Hi I have a transformer of 17 volts 15 amp, I would like to reduce to 13.8 volts 15 amp, will this circuit works for me, many thanks and more power


    Hello,is circult working proper

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