6V battery automatic charger circuit for emergency lights

The 6V battery-powered emergency lights that appear on the market come with too simple a charger, which can cause serious heat and burn easily after long-term use. It is also easy to overcharge the battery during charging, causing the electrolyte to dry out prematurely and shortening the battery life. In response to this shortcoming, the author changed it into an automatic charger. After more than half a year of use, the effect is good. The circuit is shown below: Brief description of the principle: IC provides the base voltage for the base of T1, and the relay J realizes the self-locking and automatic switching of the switch K. Power outage. After connecting the battery, press K, the power indicator light L lights up, and J is powered on at the same time. K is self-locked by its contact J-0, and charging begins. At this time, the emitter voltage of T1 is low due to the lack of battery power. At (7.5V+0.65V), T1 is cut off, T2 is also cut off, and they have no effect on T3. When the battery voltage is charged to 7.5V, the emitter voltage of T1 is 7.5V+0.65V, T1 is saturated and turned on, T2 is also turned on, the base voltage of T3 drops and is turned off, J loses power and is released, J-0 is disconnected, charging stop. Indicator light L goes out. Batteries with different voltages can also be charged by adjusting W. Diode D in the circuit is an isolation diode, which can prevent reverse discharge of the battery. Component selection: R is the charging current limiting resistor, which can be selected between 5 and 10Ω. There are no special requirements for other components. All components can be overlapped on a plastic box, and the IC does not need a heat sink. Debugging: Short-circuit K and adjust W so that the IC output voltage is 7.5V, the battery's full voltage.