Simple delay lighting circuit

The delay lighting introduced in this article is very simple and easy to install. Just connect it directly to both ends of an ordinary switch. When in use, turn on the switch and the light will light up. After turning off the light, due to the delay circuit, the light will still light up for a few seconds and then go out automatically. This circuit is safe and reliable, suitable for beginners to make their own. Circuit principle: The circuit of this delay lighting lamp is as shown in the attached figure. The delay circuit is shown in the dotted box. K in the picture is a pull switch or wall switch. When K is closed, the delay circuit does not work and the lamp is in a normal lighting state. When K is turned off, the voltage is charged to the capacitor C via R1 on the one hand. Since no current flows through R2 during the charging period of C, the transistor V is always in a cut-off state; on the other hand, the voltage is charged to the capacitor C via R3 and R4. The silicon-controlled SCR provides a trigger voltage to keep the silicon-controlled SCR in a conductive state, so the light stays on for a period of time after the light is turned off. When the capacitor C is fully charged, the transistor V changes from the off state to the on state, the thyristor SCR is turned off, and the light goes out. During the light-off delay period of this circuit, the delay time is determined by the values ​​of R1 and C. Readers can also determine it according to their own needs. The thyristor in this circuit is a one-way thyristor. During the delay period of turning off the lights, the brightness of the lamp is about half of the brightness when the lights are on, so as to meet people's visual needs and save energy at the same time. Circuit production: MCR100-8 is used as the one-way thyristor SCR in the picture, and the withstand voltage must be above 600V. The power of the light bulb should not be greater than 100W. The diode VD is 1N4007 and V is C1815. The resistors are all 1/8W carbon film resistors. During production, use a small piece of circuit board to solder the components in the dotted box in the picture. It is best to install this circuit in the groove at the bottom of the pull switch, stick it firmly with glue and connect the leads to the two terminals of the switch.