Dual input battery charger circuit


Battery chargers circuit play quite a important role in everyday life as we use variety of chargers and most of the chargers we avail from the market are quite expensive. So this circuit teaches you how to make one with same efficiency and reliability we obtain from those chargers. The above circuit was designed to give two different kinds of voltages as output and based on our requirements we can select one. As you can notice one part of the circuit works with input AC voltage other with input DC voltage.


The first part of the circuit is powered by step down transformer which converts the 230V AC into 9V. It was then fed into the bridge rectifier to convert it from AC voltage to DC voltage. Then the rectified voltage was directly fed to the output through some LED’s for the purpose of indication. The LED2 was used to indicate the Power ON and LED3 to indicate the charging( Battery was connected to the charging end). The current limiting resistor R2 was added to limit the current flow and voltage obtained from the output will be around 7.2V.

The second part of this circuit was powered by external DC power supply, where resistor R4 limits the input current to a safe value after fed into the polarity protection diode D5. Then it was fed into the IC1 7805 which gives 5V as output from the 3rd pin. A LED1 was connected through the com pin of the IC1 and it indicates that external DC power supply was used. The 5V was then connected to the output through some LED’s and resistors to limit the current value obtained from the 7805. The output voltage obtained from this part will be around 3.8V as most of the mobile batteries use 3.7-4.6V as input, this is well suited to charge up your mobile with ease. Heat sink is recommended as this type of circuits will be used for long time and produces high heat while powered ON.


You can add up any voltage regulators and resistors to limit the voltage value obtained at the output. Usage of Variable resistors allow you to utilize this circuit for wide range of voltage requirements by the battery. This two voltage range battery charger circuit provides  room to either use AC or DC supply as input. 


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Hi… Can you please tell me in the above dual power input circuit how can I automatically cut DC power supply if the AC (Transformer) power supply is on..?