Dual Mode Battery Charger Circuit Using Adjustable Positive-Voltage Regulator
Created: Mar 07, 2016
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This dual mode battery charger is a simple electronic device that features the two essential modes of a battery charger. It has both the constant voltage and constant current characteristics which both prevents overcharging in batteries. The device specifically uses the Texas Instruments’ LM317L, an adjustable, 3 terminal, positive voltage regulator capable of supplying 100mA over an output voltage range of 1.25V to 32V. It is easy to use and requires only two external resistors to set the output voltage.
The main components of the circuit are the LM317L voltage regulator and TL432 precision adjustable shunt regulator, which cause the constant voltage and current modes of the charger. The 1N4001 diode prevents battery from discharging back to the regulator if the input supply is disconnected. The resistor R5 provides current to switch the transistor when the input supply is present. The shunt regulator (D2) and the passive components that surround it determine whether the battery has reached its required voltage. When the reference input voltage of D2 reaches 2.5V, it switches on its internal transistor, making pin ADJ turns to 0V. In this condition, D2 holds U1 in constant current supply mode. In addition, capacitor C3 helps to stabilize the switching of the shunt regulator. The variable may also be adjusted depending on the peak voltage requirement of the lead acid battery.
Battery chargers have been widely used nowadays to energize secondary cells for a specific use. This device is useful in toy car batteries, flashlight and other related applications, which enable the users to save money instead of buying a new battery cells.