Touch type fade-out delay light circuit

The touch-type fade-out delay lamp circuit is shown in Figure 126. Circuit characteristics: When turning on the light, just touch the -r touch pad, and the light will turn on. After
a delay of tens of seconds
, the light will not
go out immediately, but will gradually
dim vertically until it goes out
. . The waste touch switch
can also be connected to external lead
wires, and can directly
replace ordinary light
switches without having to change the original indoor wiring.
    VDl-VD4, vs and exhaust form a power circuit, which outputs about 12V pulsating DC voltage for use by light switches.
Normally, the transistor VT3 is in the off state and the lamp E is not on. At this time, the luminescent tube I.ED emits low light, which is used for weak light illumination at night
and can indicate the position of the light switch.
    VT2 constitutes a touch electronic switch. When the light is turned on, the human hand only needs to touch the electrode sheet M, and the human body leakage current
passes through R. Inject the base of VT2 to quickly turn on VT2. The 12V pulsating voltage charges G through VT2 and
charges the voltage at both ends of C: to about 12V. The electronic rheostat VT1 is electrically conductive, and the 12V pulsating voltage flows through R to
C, allowing electricity to start the relaxation oscillator composed of vU. The single-junction transistor vu outputs a sharp pulse and adds it to
the gate of the thyristor VT3, causing VT3 to quickly turn on, and the lamp E is lit. Due to R. The value is small, and
the conductor voltage drop of VT1 is small, the oscillation frequency of the relaxation oscillator is high, the conduction angle of thyristor VT3 is large, and it is almost turned on at full voltage
, and the lamp E is in a fully bright state. After the human hand leaves the electrode sheet M, C. Through R, it discharges to VT1, keeping VT1
on. As time goes by, C. As the discharge current decreases, VT1 exits the conduction state and enters the amplification state, and
its tube voltage drop increases. Equivalent to C. A large resistor is connected in series in the charging branch, so
the time of the vu output spike pulse is delayed, the conduction angle of VT3 is reduced, and the brightness of the lamp E becomes smaller. At this time, the lamp enters the dimming stage. As
the Cz discharge current continues to decrease, the equivalent resistance of VT1 gradually increases, the conduction angle of VT3 continues to decrease, and the light
becomes darker and darker. When the Ct discharge current decreases to a certain value, VT1 changes from the amplified state to the cut-off state, vu
stops oscillating, the thyristor VT3 turns off, and the lamp E goes out. Each time M is touched
    in the circuit , the lamp can light up for about 45 to 60 seconds. If you want to change the delay time, you can adjust
the resistance of resistor R. The larger the resistance of R a, the longer the delay time, and vice versa. (Please do not adjust R.
and C. when adjusting the delay time, because these values ​​​​will affect the length of the dimming time, so adjust R..) The dimming phase time of the switch is determined
by the capacitor C. Adjustment, C. The larger the capacitance value, the longer the time it takes to fade from dark to light, and vice versa.