Now a day’s many LED Torches and Emergency lights are using in Home which are powered by 3.6 Volt rechargeable battery. Due to improper charging, battery will damage and the torch becomes useless. In many of the makes, a Transformerless power supply is used to charge the battery but it may easily fail due to voltage spikes in the mains line. So here is a simple battery charger for all kinds gadgets using 3.6 V battery.
A 4.5 Volt 500 mA transformer is the main part of the charger. It is commonly used in Radio and Cordless phone adapters. Two Diodes (D1 and D2) rectifies the low volt AC to DC and the Smoothing capacitor C1 filters the ripples. Output from the rectifier – capacitor junction will have around 500 mA current which is too much for charging. Since slow charging with low current is a good method, a current limiting resistor R2 is added. Output will be 4.5 volts at 73 mA current. You can change the value of R2 for different current.
Output voltage from the diodes will be 5.6V so the voltage across R2 will be 1.1V. Therefore the current at the output will be 1.1V / 15 = 0.073 Amps or 73 mA
Make this external charger by enclosing the circuit in an adapter case. Connect a suitable pin for the socket provided in the Gadget for external charging.