Light controlled delayed lighting

Changing the resistance of RP can change the base potential of transistor VT1, so it can be used to adjust the light control sensitivity of the circuit.
    The circuit of the light-controlled delayed lighting lamp is shown in Figure 1-32. The right part of the dotted line in the figure is the ordinary lighting circuit, and the left part is the newly added part
. S is the original switch of the lighting lamp , which can still control the on and off of the electric lamp H. When S is closed, the light H will light up; when S is turned on,
the light will go out. At this time, the light H has a light control delay function.
    After the 220V AC power is VD1 half-wave rectified, Rl current limiting, VD2 voltage stabilizing and CI filtered, it outputs about 24V DC
voltage for the control circuit. When other lights are on during the day or night, the phototransistor VT is in the on state, the thyristor VS
has no trigger voltage and is in the off state, and the light H does not light up. When the indoor light is turned off and the light suddenly dims, VT loses light and is in a cut-off
state. The positive terminal potential of C2 jumps high. cl charges C2 through the gates of R2 and vs. This charging current serves as the
trigger to turn on vs. The light H-energized (half-wave alternating current) emits soft light. As charging proceeds. The charging current of C2
gradually decreases. When this current is less than the minimum trigger current of vs, vs turns off when the alternating current crosses zero, and the light H goes out
. However, during the natural transition from daytime to darkness, since the light dimming is not sudden but slowly dimming,
the positive terminal potential of C2 slowly increases as VT is gradually cut off, and its charging current is always less than the minimum trigger of vs current, so H will not
be lit. When it gets dark or when other lights in the room are turned on again. VT is turned on when exposed to light, the potential of the positive terminal of C2 decreases, and
the charge stored in C2 is discharged through VT and VD3 to prepare for the next delay in lighting when the lights are turned off.
    The length of circuit delay lighting time is mainly determined by the values ​​​​of R2 and C2, and secondly, it is also related to the photoelectric parameters of VT and
the minimum trigger current of vs. According to actual measurement, the delayed lighting time of this circuit is 1~1.5min. The power consumption of the circuit itself is extremely small, and the actual measured power
consumption is about 0,1mA. It can be considered that it consumes no power.