Timing control circuit (6)

(1) Introduction to the circuit principle The timing controller introduced in this example has delayed turn-on (continuously adjustable from 0 to 200min), delayed turn-off (
continuously adjustable from 10 to 210min) and intermittent cycle control functions, and can be used for electric heaters and Control of single-phase AC motors.
  The timing controller circuit consists of a power supply circuit, a timing control circuit and a control execution circuit, as shown in Figure 3-50.
  The power circuit is composed of power switch Sl, fuse FU, power transformer T, rectifier diodes VD1-VD1, filter capacitors G, Cs and three-
terminal voltage stabilizing integrated circuit IC 1.
    The timing controller circuit consists of time base integrated circuits IC2, IC3, and resistors Ri-Ri. , capacitor C, ~G, potentiometers RP1, RP2, transistors
VT1 ~ VT4, light-emitting diode I. It consists of ED1, LED2, manual discharge button S2 and function selection switch S3.
    The control execution circuit is composed of diode VD5, relay K and AC contactor KM.
    After the power switch Sl is turned on, the AC 220V voltage is stepped down by T, rectified by VD1~VD4, filtered by G and stabilized by IC1, and a +12V
(v[,:) voltage is generated, which is used as the working power supply of the timing controller circuit.
    If the power supply of the controlled load needs to be turned on with a delay, S3 should be placed in the "1" position to short-circuit the collector of VT3 to ground, adjust RP1
to set the time required for the delayed turn-on of the load power supply, and then connect it again S2. The timer starts counting. IC2 is triggered and set, pin ③ outputs high level,
turning on VT4, IC 3 is forced to reset, its pin ③ outputs low level, K and KM do not pull in, and the power supply of the controlled load is disconnected. At this time,
LED1 does not light up. LED2 lights up.