Touch Delay Lighting Switch (1)

Normally, the transistor VT1 is in a cut-off state because the resistor Rl is grounded. Its collector is at high level and VT2 is turned on. The gate and cathode of
the thyristor vs are short-circuited by the ce pole of VT2, so vs is in the off state and the lamp H is not connected. Bright. At this time,
the light-emitting diode LED indicates the position of the switch, making it easier for people to find the switch at night .
    When the human hand touches the electrode sheet M, the clutter signal induced by the human body changes VT1 from the original cut-off state to the on-state, and its
collector becomes low level, VT2 cuts off, vs obtains the trigger current through the resistor R4, and the light turns on. H is energized and emits light.
At the same time, capacitor C is short-circuited by VT1 and cannot be charged. When the human hand leaves the electrode sheet M, although VTI quickly returns to the cut-off
state, since the voltage across the capacitor C cannot suddenly change, VT2 continues to remain in the cut-off state because the base is still low, so
the lamp H still lights up and does not go out. . At this time, the power supply continues to charge the capacitor C through R3, causing the base potential of VT2 to continue
to rise. When this voltage rises to 0.65V, VT2 changes from the original cut-off state to the on-state, so the thyristor vs loses the trigger
voltage. , when the alternating current crosses zero, it is turned off and the lamp H goes out.