[Pictures] Homemade simple emergency light

A sudden power outage at night will bring inconvenience to your life. The emergency light circuit in this article is simple and low-cost. As long as the city power is off, the emergency light will automatically light up, bringing convenience to your life.

Working principle: The circuit is shown in the figure. After the 220V mains is stepped down by transformer T and rectified by VD1, a DC voltage of about 9V is obtained on capacitor C1. This voltage charges the battery through VD2 and provides base bias for V1 through resistor R2, making V1 saturated and conducting, V2 cut off, and light bulb H does not light up. When the mains power is suddenly cut off, the voltage across C1 disappears. Due to the isolation effect of VD2, no current flows through R2, and V1 is cut off. At this time, the positive pole of the battery provides base current to V2 through R3 to make it conduct, and light bulb H lights up. R1 and LED form a power indication circuit.

Production and debugging: There are no special requirements for all components. The transformer can use a small transformer of 3~5W. V1 uses 3DG130 with a β value greater than 50. V2 uses 3DD15 with a β value greater than 30. H can use a 3V small light bulb. This circuit is easy to debug. As long as the welding is correct, it can work after turning on.