5V Transformerless DC Power Supply from 220V with LM2575

Transformerless Power supply with LM2575

Is often required to supply electricity to the consumer low voltage 220V.  You can use an external adapter – but it’s bad, and to reduce the size of the device requires a power supply located in the device.

This 5v power supply used LM2995 to the converter circuit which can be connected directly to 220V.  To do this,  AC converted to DC voltage across the diode bridge VD1,  and then lowered to 40V.  Above 40 V we should not use it,  due to the fact that the LM2995 maximum input voltage must not exceed 45V.

Transistors T1 and T2 form a pulsating stress amplitude up to 40V, which depends on the zener diode D1. This pulsating voltage is applied to the capacitor C1, which is slightly smoothed. Next on the chip down-converter output voltage is stabilized, defined applied chips : so for LM2575-5 5V it will be equal.  Schottky diode D2, L1, C2 and C3 are the standard strapping of the chip.

7 comments

    1. Hi Liam.

      T1 should be standard NPN transistor – BC547 (TO-92) and T2 is BUZ41a (TO-220) or You can use IRF730.
      Also, my recommendation for R3 is to use higher power one, 2W would be fine.

      Circuit is connected directly to the MAINS voltage and it’s all over components, so it is very dangerous to use!
      All parts are LIVE and should never be touched, neither wires while you connecting load to this power supply!

      Greetings from Serbia.

  2. Hi
    Could any body suggest me the resistor R1,R2,R3,R4 & R5 , D1 , T1 & T2 values for an output voltage of 25V which is given as input to the LM2575. And also pls suggest me the VD1 rectifier component name and its specifications for current rate of 2A.

    1. As I know this power supply is “Elektor” design, and they said it’s capable for 1A!
      I have build it 3pcs, few months ago, and they are working excellent, but connected loads draw “only” 400mA , everything is cool. I have added small heatsink to T2, but don’t know is it even necessary?

      Be careful, connected to main’s voltage and don’t touch any parts during work !!!

  4. Very interesting circuit, however, a think it is not going to work very well, look at T2 ( BUZ41A or IRF730) , both have a maximum 20V VGS, so when voltage get bigger than 20 , T2 gate get damage .

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