Touch self-extinguishing circuit analysis

The touch-type self-extinguishing circuit can be installed in the bedroom without turning off the lights and then going to the bed. It can also be used in stairways or toilets, which is convenient and convenient.
Line principle: Transformer B output 12V AC power is converted into DC power supply transistor BG1~BG3 through diode D1 half-wave rectification. Normally BG2 is in the off state, so the composite tube composed of BG2 and BG3 is also in the off state, relay J does not operate, and the electric lamp does not emit light. . A is a touch electrode sheet, and N is a bubble. When the human hand touches the electrode sheet A, the human body capacitor and the C2 partial pressure cause the bubble N glow to ignite, and the BG1 has a base current injection and the C3 is also filled with the charge. The relay J is energized, and its normally open contact j is sucked. The electric light therefore illuminates. When the person leaves the electrode A, the bubble N is extinguished and BG1 is turned off. Since the stored charge of C3 is discharged to the junctions of BG2 and BG3 through R3, the composite tube can still maintain the conduction state, until the C3 charge is substantially discharged, the composite tube is turned on and off, j jumps, and the light is extinguished.
The function of the resistor R2 is to make the BG1 normally reverse biased to reduce its leakage current. I. If there is no R2, the leakage current of the BG1 is continuously charged to the C3, and at a certain time, even if the human hand does not touch the electrode A, The composite pipes BG2 and BG3 will automatically enter the conduction state, which will cause the lights to be always on. After setting R2, the leakage current of BG1 is very small, and the C3 capacitor itself leaks, and the voltage across C3 cannot rise to the extent that the composite pipe is connected. Thus, the electric light can only be illuminated when the electrode A is touched.