Light controlled delay circuit (5)

This example also uses a battery-powered light-controlled delayed lighting lamp. When the lights are turned off at night or suddenly stopped, the lamp will
light up automatically for about 30 seconds, which is very convenient for life. Its circuit is shown in circle I 208.
    The VDP in the circle is a photosensitive tube that exhibits low resistance when exposed to natural light during the day, and the transistor VT is cut off.
The screw terminal ⑤ of the rWH8778 power switch integrated circuit is at low level , its internal electronic switch is off +F, and the small electric
bead E does not light up. If the lights are turned off at night or
there is a sudden power outage. VDP suddenly changes
to high resistance without light exposure, VT turns on quickly, and its collector
outputs a high level. This high level is differentiated by
R, (1.) so that the 5th
pin of TWH8778 obtains a stop
pulse , its internal electronic switch tube is connected,
that is, the ① pin is connected to the ③ and ③ pins, and the electric bead
E is energized and emits light. At the same time, the stop source can
charge to C through VD1 and R. This
charging current can maintain the TWH8778 The potential of pin ⑤ remains above 16V, so 1: can remain lit.
After about 30 seconds, the o charge is fully charged. The pin ⑤ of TWH8778 returns to low level , and the electric bead E goes out.
At the same time (1z stored charge can be passed through R , VD2 and F are discharged to prepare for the delay of the next time the lights are turned on.
    The non-lighting condition of this circuit is that only when the lights are suddenly turned off at night, the electric bead E will light up. However, the
natural Light up the electric bead F, because the light gradually dims when it gets dark, VT gradually transitions from the cut-off state to
the on-state, R, the upper voltage gradually increases, due to the DC blocking effect of the lower c, the circuit will not be Trigger work. In the picture,
SB is the manual light button. Regardless of day or night, as long as you press SB ~ times, E will light up for about 30 seconds.