Delay light circuit using relay (6)

It is a very versatile delay light circuit. When it is flat, no current flows through relay K, its moving and closing
contact k-2 is open, and the light E does not light up. When you need to turn off
the light, just connect
the
button well This DC current passes through the moving contact kl of the relay to quickly fill the capacitor (j) with charge, and provides a base bias current to the transistor VT1 through the resistor R , causing VTI and VT2 to quickly saturate and conduct, and the relay K is electrically activated, and its moving closing Contact k 2 is closed, making the relay self-locking, and at the same time, the open contact kl jumps up. If you release SRI or SB2 at this time, the lamp E can still light up. This is because the charge stored in c can be transferred to vri through R The emitter junctions of VT1 and VT2 are discharged to maintain their saturated conduction. As time goes by, the charge stored in C becomes less and less. When it is small enough to maintain VT1 and VT2 conduction, the relay K releases and its contacts are reset. , that is, kl is closed, k2 is opened, the circuit returns to the initial state, and the light E goes out. The length of the circuit delay time is mainly determined by the discharge time constant of R and (j. The amplification factor of the transistor VT1 and VTt also has an impact on the delay time, p The larger the value, the longer the delay time. When the anus of VT1 and VT2 is 100 , using the graphic data, each time the key switch is pressed, the lamp E can light up for about iOmin.