Delay light off circuit principle

Delay light off circuit principle

　　The circuit working principle of the device is shown in Figure 4. When the push button switch AN is not pressed, the transistor VT has no bias current and is cut off. At this time, the c-e inter-electrode resistance of VT is greater than 50K, so the ① and ② pins of LSE are equivalent to an open circuit, the ④ pin of LSE outputs a low level, and the relay J is in a released state. When the switch AN is pressed, its current quickly charges the capacitor C3 through AN, and the charge is fully charged within 1 second. At this time, the transistor VT is turned on, and its inter-electrode resistance is reduced, so the LSE is turned on, its ④ pin outputs a high level, the relay J is energized and attracted, and the lamp H is lit. After releasing the hand, the charge in C3 is discharged to VT through the resistor R to maintain the conduction of VT. When the charge in C3 is discharged, VT is cut off, J is automatically released, and H is extinguished. The lighting time of the lamp H depends on the values ​​of R and C3. According to the values ​​shown in Figure *, the delay time is about 1 minute and 30 seconds after testing.