desktop linear power supply

Desktop PC Linear Power Supply Circuit

Useful for electronics hobbyists, this linear workbench desktop power supply circuit converts a high input voltage (12V) from the SMPS of a PC into low output voltage (1.25 to 9 volts). An adjustable three-pin voltage regulator chip LM317T (IC1) is used here to provide the required voltages. The LM317T regulator, in TO-220 pack, can handle current of up to 1 amp in practice.

Desktop PC power supply circuit diagram

desktop linear power supply

The diagram shows the circuit of the desktop power supply. Regulator IC LM317T is arranged in its standard application. Diode D1 guards against polarity reversal and capacitor C1 is an additional buffer. The green LED (LED1) indicates the status of the power input. Diode D2 prevents the output voltage from rising above the input voltage when a capacitive or inductive load is connected at the output. Similarly, capacitor C3 suppresses any residual ripple.

Connect a standard digital voltmeter in parallel with the output leads to accurately set the desired voltage with the help of variable resistor VR1. You can also use your digital multimeter if the digital voltmeter is not available. Switch on S1 and set the required voltage through preset VR1 and read it on the digital voltmeter.
Now the power supply is ready for use.

The circuit can be wired on a common PCB. After fabrication, enclose the circuit in a metallic cover. Then open the cabinet of your PC and connect the input line of the gadget to a free (hanging) four-pin drive power connector of the SMPS carefully.


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  • V.Sambath kumar

    Hi Marian,

    Very good compact circuit ,

    you can still improve the standard of this circuit by

    1. provide a diode IN5402 on the +ive out put terminal for polarity protection as you have taken care in the v in put side.(Cathode of diode
    going to the oup put terminal.

    2.Provide a .22 pol 25or 35v across the yellow and black wires ie v in put from smps to avoid transient voltage spikes which can occur fr the smps.

    3.provide s1 on the in put side of the yellow wire by which you will not load the cap c1 and the led if at all you want the led to be on continuously when the pc is on provide S1 before D1.

    4.C3 should be a tantalum cap for more accurate out put.

    4 can also provide a fuse for the dc voltage out put.
    These are all minor things that you may know ,but i take the chance to
    remind you to recollect the above which you might have forgot to incorporate in your ckt.

    Thank you very much,

    Regards, V.Sambathkumar.

  • jay

    R3 should be 1.8K not 18K.

  • Sayanti

    Is it applicable in our PC?

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