102450 polymer battery constant current charging circuit diagram

　　The nickel-metal hydride battery constant current charging circuit can charge 1 to 6 nickel-metal hydride batteries (or nickel-cadmium batteries) with constant current (the charging current can be set), and can automatically identify whether the polarity of the nickel-metal hydride battery is wrongly connected. When the positive and negative poles of the battery are connected incorrectly, this circuit will have no charging current output and the LED indicator will not light up, thus protecting the nickel-metal hydride battery from damage due to polarity connection. This circuit is designed with triode discrete components. It is simple and low-cost, and is very suitable for electronic beginners to make by themselves.

　　The low-power red LED is here not only used as a charging indicator light, but also as a voltage stabilizing component, providing a -1.7V to the base of VT2 (the forward voltage drop of the low-power red LED is generally 1.6~1.8V, and is relatively stable. It can be used as a low-voltage voltage regulator tube) to maintain a stable voltage of about 100%. Since the emitter junction voltage drop of VT2 is about 0.7V, the voltage across R3 UR3 = 1.7V - 0.7V = 1V. Since UR3 is relatively stable, the current Ih (ie, charging current) flowing through R3 can be regarded as a constant current. . Ih=1V/R3=1V/2Ω=0.5A. Adjusting the resistance of R3 can change the charging current of the battery.

　　Resistor R1 is the current limiting resistor of the LED. When no battery is connected to the circuit, the emitter junction of VT1 has no bias voltage, so VT1 is turned off, the LED will not light up, and the controllable constant current source composed of VT2 will not work. When the battery is connected to the circuit for charging and the polarity is not connected incorrectly, VT1 obtains the bias voltage and is turned on, the LED indicator lights up, and the controllable constant current source composed of VT2 works to charge the nickel-metal hydride battery.

　　If the positive and negative poles of the battery are reversely connected during charging, the emitter junction of VT1 will be reverse-biased and cut off. The controllable constant current source formed by VT2 will not work and there will be no charging current output, thereby protecting the nickel-metal hydride battery.

　　Simple constant current charging circuit diagram of nickel metal hydride battery

　　Generally, the nominal voltage of nickel-metal hydride batteries is 1.2V, the discharge end voltage is 0.9V, and the charge end voltage is around 1.4V. This kind of battery can generally be charged with constant current. A simple constant current charging circuit for nickel-metal hydride batteries is given below, which can use a 5V mobile phone charger to charge a single nickel-metal hydride battery.

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