Sep 172014

Transformerless Power Supply Circuit

We will use a zener diode among other elements to acheive the Transformerless Power Supply circuit. The use of a zener diode means that our power supply will give a current value in a limited range (it will be a maximum and a minimum posible current that the circuit can give).

This power supply is designed to be connected to a specific circuit and it is not normally used with a changing load, because as noted before, it can not give a current that changes too much. In other words, this power suply must be connected permanently to the circuit as a whole unit. If you want to disconnect it, you must disconnect the whole unit.

Transformerless Power Supply Circuit Diagram

The Transformerless Power Supply circuit is made of:

  • A Zener diode (D3) to maintain a constant voltage on the load.
  • Two semiconductor diodes (D1 and D2) to form a ½ wave rectifier.
  • A capacitor (C2): It is a filter capacitor to “smooth” the signal that is coming out from the rectifier diodes and before it is applyed to the Zener diode.
  • The resistor R2 and the capacitor C1: together they will serve to reduce the input voltage (either 110 or 220 volts AC, 50 or 60 Hertz) to the level that is acceptable to the Zener diode.

The voltage drop occurs in R2 and on the capacitor C1. In C1 the voltage drop is due to the capacitive reactance which depends on the value of the capacitor and the frequency of the applied signal (50 Hz or 60 Hz). The original design was made thinking that we have a 220 volts, 50 Hertz input signal but it was tested with 110 Volts, 60 Hertz and it runs smoothly. The resistor R1 is included to assist on the unloading process of the capacitor when the circuit is disconnected. This circuit can deliver no more than 100, 120 milliamps

Note: Caution! The circuit is connected directly to the main voltage (110/220 Volts), which means that we must take extra care when making the tests.

Components List

  • 1  Zener diode from 4.7 to 5.6 Volts (D3)
  • 2  Common rectifiers diodes 400 Volts / 25 amps (D1, D2)
  • 1  100K to 120K resistor (kilohms), (R1)
  • 1  33 Ohms resistor, (R2)
  • 1  2.2 uF / 250 volts capacitor, (C1)
  • 1  220 to 1000 uF (microfarads) electrolytic capacitor, (C2)


  2 Responses to “Transformerless Power Supply circuit”

  1. Hi can you suggest a circuit from 220 volts ac to 120 volts ac at 60hz. To power a 110volts AC 10 watts light bulb.
    Thank you very much in advance.

    • Hello

      I’m not sure I understand the question.

      I think it is only necessary to use a 220 to 110VAC transformer, between 220VAC and the 10 watts bulb,

      If that’s not what you want to know, please clarify the question.


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