Delay light circuit using relay (4)

A delayed light circuit using relay control. When opening the state, just press SR once and the electric light
E will light up. At the same time, the 220V AC
power
is rectified by I, step-down, vr)i-VD4 bridge type, and a DC voltage
of about i2V is obtained at both ends of (1.)
. Transistors
VT1 and VT2 are connected to form an
asymmetric bistable trigger ,
pour R.
The resistance of the wire package of relay K is basically the same, but . <
R., so VT2 is turned on, VT1 is turned off, relay K is energized, and its contact kl is closed, making the circuit self
-locking, so the light E continues It emits light when it is powered on. Then, 12V DC passes through the RP Q} capacitor (1, charging lH, so that
the voltage at both ends of c: continues to rise. When it rises to the conduction peak voltage of vu, vu is turned on, that is, to the base of VTI pole
input, forward pulse, forcing VT1 to conduct, Vl, 2 to cut off, that is, the bistable flip-flop flips, K is released, its
moving contact kl jumps open, and the light E goes out. By adjusting the resistance of RP, the desired The required delay time.
    K can use JZC-22F, DC12V small medium-power electromagnetic relay , whose wire package resistance is 400fl and contact
capacity is 5A. VT1 and VT2 are required to use 901 3-issue silicon NPN diodes with the same characteristics as possible, p
The values ​​are all around 100. Note: The value of VT1 cannot be higher than VT2, otherwise the circuit will not be able to work normally.