Switched-mode power supply tutorials

A switching-mode power supply (SMPS) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Switching regulators are used as replacements for linear regulators when higher efficiency, smaller size or lighter weight are required. The main advantage of the switching power supply is greater efficiency than linear regulators. The downside of them are that their circuits are more complicated than linear power supplies and their switching currents can cause electrical noise problems if not carefully suppressed. If the SMPS has an AC input, then the first stage is to convert the input to DC.

Here are some tutorial videos on switched-mode power supply technology:

How Does a Switching Power Supply Work 1 (schematic, explanation, example, modifications)

How Does a Switching Power Supply Work 2 (measurements)

How Does a Switching Power Supply Work 3 (CCM vs. DCM)

Simple 12V 1A LED Power Supply – with schematic and transformer autopsy

12V 5A LED switching power supply – with schematic

12V 5A Switching Transformer Autopsy – How it’s constructed? Is it safe?

Howto repair switch mode power supplies #1: basics, and block diagram of a PSU

Howto repair switch mode power supplies #2: Stand-by circuit and its functionality


  1. buon hang thung xin says:

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  2. Tomi Engdahl says:

    Mains powered SMPSU repair tips from

    Very easy to check it if you have the tools. A variable PSU with current limit can be used to power it up, by apply 24V 1A directly connect it to the 400V caps lead. Make sure polarity is right or you will further damage more components on the board. Bypass the Vcc pin of pwm contoller ic with a 100 ohm resistor to the positive supply of 24 V. Check the output gate driver. Also check the MOSFET. That’s one of the culprit in failed smps. PTC and the rectifier diodes at the primary side also need to be checked. Any bulging caps need to be replaced with the same specs. Don’t forget check the fuse.

  3. Tomi Engdahl says:

    SMPS repair:

    First – cleaning.
    Second – recap.
    Third – diodes.
    Fourth – the output transformer.
    And then … imagine.

  4. Tomi Engdahl says:

    Modify 12V power supply to 24V 36V 48V

    I am building a bench power supply. So today I bought two 24V / 10A power supplies. A 36V or 48V power supply is twice as expensive as a 24V power supply . So I bought the 24 power supply and modified it to 36V. The modification is very simple, you just need to replace feedback resistor (in my power supply. it is 2K, I replace it to 1K). Next you need to replace the 35V filter capacitors to 50V or 63V. For a 12V power supply, do the same.

    It should be pointed out that you will be dropping your current capability by at least half doing this. So you will need a power supply that will be at least double what you need in your final application.

    If you bought a 12V 10A supply, it is capable of 120 watts. If you modify it to 24V, it would be 5A max because the power supply is still only capable of 120 watts.

    Apart from the fan which was not designed for 36v, you should check the dissipation rating of the two resistors in the potential divider you changed – lowering the resistor value will increase the current flowing and the top resistor will also see the increased output voltage.

    Very informative. You are pretty careless with your handling with mains connected. Those terminals ar
    not reliable and you didn’t test the integrity with even a small ‘pull’ after connection. a mains wire slipping out
    can do damage to the case or to you …depending on the situation.


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