Automatic power off charger circuit schematic

Photocoupler

description:

This self-made charger can charge one battery of rechargeable battery for BP every time, it can automatically power off, easy to use, safe and energy-saving.

working principle

The whole circuit is composed of rectification and filtering, constant current charging and timing control circuits. Since the accuracy of the timer is not high, a simple rectifier circuit can be used. The charging part adopts constant current charging, and the circuit is simple and the effect is good. The timing part uses a composite pipe working mode.

When S is pressed (S-1 and S-2 are simultaneously turned on), 220V AC is stepped down, rectified and filtered by T, VD1~VD4, C1 to obtain 12V DC voltage. 12V DC voltage provides charging voltage for VD5, R1 and LED. At the same time, C2 is charged by S-2, VT1 and VT2 are turned on by R2 and R3, K is electrically operated, and K-1 is connected. At this time, S is released (S-1, S-2 are disconnected). Due to the discharge of C2, VT1 and VT2 are still in an on state. After C2 discharge is completed, VT1, VT2, and K stop working, K-1 is disconnected, and the entire circuit stops working. VD5 is used to prevent reverse discharge of the rechargeable battery. LEDs are used for circuit operation and charging instructions. R2 is used for timing adjustment, and the adjustment range is 10~16h. VD6 is used to protect VT1 and VT2.

Circuit fabrication and component selection

For ease of installation, T uses a small power transformer. R1 is the charge current limiting resistor. When using the No. 5 rechargeable battery, R1 takes 90 ohms; when using the 7th rechargeable battery, R1 takes 120 ohms. 90 series triodes are also available for VT1 and VT2. K uses a small 12V relay. S uses the double-knife self-reset button switch to remove the self-locking part of the ordinary double-knife self-locking power switch.