Power outage emergency light (1)

Normally, the switch S is in a closed state. When the power supply from the grid is normal, the 220V AC mains power is stepped down by the transformer T,
rectified by VD1, filtered by Cl, and charged to the battery G through R3 and LED 2. LED1 is the mains power indicator light . The LEDI glow indicates that the mains
power supply is normal. LED2 is the battery charging indicator light . LED2 lights up to indicate that the battery is charging. When the mains power
supply is normal. VTI obtains base bias current through R2 and is turned on. Its collector, the base of VT2, is at a low potential, so VT2
is cut off and the lamp H does not light up. When the mains power suddenly fails, LED1 and LED2 are extinguished one after another. Due to the isolation effect of LED 2, battery G will not supply power
to the base of VT1 through R3 and R2 . VTI is cut off due to the mains power failure, thereby releasing the blockade of VT2 . The base gets a bias current from the battery G through R4 and is turned on, and the emergency light H is energized and emits light.