LED lit from Mains

               Lighting LEDs using battery are not convenient especially in the case of decorating lights (LED), since they are lit continuously for days. So we need another power source which provides power continuously for day. Power from the mains is a better option, but the main power supply is of high voltage (~220V, AC). One method is to use a step-down transformer then a rectifier, a bridge rectifier. But this method is bit costly. Another method is to use a capacitor. This is the most apt method since it is much economic (this method is not recommended for high power consuming appliances).

Transformer less power supply

               A transformer less power supply can be made possible by using a capacitor. The capacitor C1 is connected in series to reduce th current as adding a resistor for decreasing current in the case of dc circuit. The capacitor here has an impedance (reactance) of  where F is the frequency and C is the capacitance of the capacitor. The capacitor is then connected to a bridge rectifier to convert the ac to dc. The rectified output of the dc from the rectifier is connected to the LED.

            

   The value of the capacitor is based on our need. According to Ohm’s Law,  . For ac circuits, , where Z is the impedance due to the capacitor, C1.

Construction

Materials required:

1)      R1= 220 Ω

2)      R2= 1MΩ

3)      C1= 470nF,400V, Polyester capacitor

4)      C2= 10uF, 16V-50V, Electrolytic capacitor

5)      D1= LED (any colour)

6)      BR1= Bridge rectifier made using the diode IN4007

The proto circuit is given below.