Touch delay light switch circuit (4)

It is a "one-line system" contact mode delay light switch with good performance. It has the following characteristics:
reasonable lU circuit design, small individual discreteness, small delay time error between each finished product, and is therefore suitable for
mass production .
  The diodes VDl -
VD4 and the thyristor VT4 form
the switch t return hoof, and
I.ED and vs form the secondary
circuit; the control loop is composed of
transistors VTI-VTS and other components
. Normally, I and ED light up
to indicate the position of the touch light switch
, making it easy to find the switch at night. The collector of VT3 is clamped by vs around sv, and VTl-VT3 are all
in the cut-off state. VT4 is in the off state when there is no trigger voltage, and the discharge E does not light up. When you need to turn on the light, H needs to
be used to touch the touch electrode M, because the leakage current from the human body passes through R. and R. After dividing the voltage, it is injected into
the base of j-electrode transistor VT3, causing VT3 to turn on quickly. The sv DC current passes through c of VT3. To (1, charge, and through R,
VT2 is turned on, VT1 is also quickly turned on, VT4 is turned on because f J_1 obtains a positive trigger current, and the lamp F
is lit. After the person F leaves the electrode HM, Tian (,. The stored charge passes through R and discharges to the VT2 emission junction, so
the conduction of VT2, VT1 and VT4 can still be maintained, and the lamp E is still lit. Until the C charge base rate is discharged,
VT2 changes from conduction to cut off, VT1 will also cut off, and VT4 will lose the trigger current. When the alternating current crosses zero f
, it will cut off and the light will go out. Changing the values ​​​​of R", R, and C'¨ can adjust the length of time the lamp is lit each time. .Using
the data shown in H, every time the electrode piece M is touched, the lamp E can light up for about 60 seconds.
    The function of the resistor R is to keep the diode VT3 in a reverse biased state at ordinary times to reduce the leakage current of VT3.
Make sure that VTZ is always in the cut-off state when there is no touch signal. If R is canceled, the quality of the round VT3 tube is often
poor, and its leakage current can cause the voltage at the capacitor Cz terminal to continue to rise, eventually causing VT2 to mislead the lamp
E. Bright.