Transformerless Power Supply circuit

Transformerless Power Supply Circuit

We will use a zener diode among other elements to achieve the Transformerless Power Supply circuit. This  means that our power supply will give a limited range current value (it will be a maximum and a minimum possible current that the power supply circuit can deliver).

This power supply must be permanently connected to the circuit as a whole unit. If you want to disconnect the circuit, you must disconnect the whole unit.

How the transformerless Power Supply circuit works?

• A Zener diode (D3) is used to maintain a constant voltage on the load.
• Two semiconductor diodes (D1 and D2) to form a ½ wave rectifier.
• A filter capacitor (C2) is used to “smooth” the signal that is coming out from the rectifier diodes and before it is applied to the Zener diode cathode.
• The R2 resistor and C1 capacitor are used to reduce the input voltage (110 or 220 volts AC, 50 or 60 Hertz) to the level suitable for the Zener diode.

There is a voltage drop on R2 and on C1 . C1 voltage drop is due to the capacitive reactance (Xc) which depends on the  capacitor value and the frequency of the applied signal (50 Hz or 60 Hz). The original design was made for the 220 volts, 50 Hertz input signal case, but it was tested with 110 volts, 60 Hertz and it runs smoothly.

Xc = 1/(2.π.f.C), where:

• Xc = capacitive reactance (ohms)
• π = 3.14159265359
• f = 50 or 60 (hertz)
• C = capacitor value (farads)

The resistor R1 is included to assist in the unloading process of the capacitor C1 when the circuit is disconnected. This circuit can deliver no more than 100 or 120 milliamps.

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

Components list for Transformerless Power Supply circuit

• 1  4.7 to 5.6 volts Zener diode (D3)
• 2  400 volts / 5 amps common rectifiers diodes (D1, D2)
• 1  100K to 120K (kilohms) resistor (R1)
• 1  33 ohms resistor, (R2)
• 1  2.2 uF / 300 volts or more capacitor, (C1)
• 1  220 to 1000 uF (microfarads) electrolytic capacitor, (C2)