USB NiCd Battery Charger Circuit

We may use AA or AAA size batteries in different applications and appliances, we can replace and cut costs on those batteries by Ni-Cd batteries. Yes it is rechargeable and can be used in traditional way, As we know nickel cadmium battery termed as Ni–Cd battery or NiCad battery in those nickel oxide hydroxide and metallic cadmium used as electrodes.




Here USB powered NiCd Battery Charger circuit designed by using few easily available components. The input power source of this charger circuit is 5V 1A from the USB-A port and the charging output is 1.2V 120mA which can be easily charged to the battery. Here two batteries are connected in series.

Circuit Diagram

BOM

S NODesignatorValueQuantity
1USB-A1
2Transistor2N22222
3D1 ZenerdiodeBZx55C1
D21N40071
D3,D4LED2
4R11kΩ1
R210Ω1
R32KΩ1
5C100μF1

Construction and Working

To Construct this circuit you can use either USB A Receptacle or USB A cable Make sure not to short circuit D+ and D- lines. VBus (+5V) and Gnd lines will be used as input power source to this circuit and Capacitor C1 acts as filter element. Q1 transistor acts as current limiting element and provides up to 120mA current at output through reverse voltage protection diode D2. Here LED D3 (use any color as you want) indicates the Charging. Zener Diode D1 Regulates the voltage to 2.7V, Whenever the batteries are full then VBE of Q2 changes and makes Q2 Turn ON So the voltage to the base of Q1 ground through Q2 transistor this will make LED D4 Glow and LED D3 OFF. You can change the Sensitivity level of full charge or over charge by adding Variable Resistor instead of R3.

This circuit is designed to charge only two NiCd batteries with 1200mA current ratings, if you are using more than two or NiCd battery pack then you have to modify the charger circuit elements based on you target battery ratings.




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