Timing control circuit (4)

(1) Introduction to circuit principle The timing controller introduced in this example can regularly control electrical equipment such as motors according to the time set by the electronic alarm clock.
Its timing time has three levels to choose from: 15min, 30min and 60min.
    The timing controller circuit consists of a power supply circuit, an input control circuit, a timing circuit and an output control circuit, as shown in Figure 3-48.
The power supply circuit includes a step-down capacitor C and a bleed resistor R. It consists of bridge rectifier uc, filter capacitor G, bar and zener diode vS.
    The input control circuit consists of the piezoelectric ceramic piece Bc and capacitor C on the electronic alarm watch. , transistor VT1 and resistor R. composition.
    The timing circuit consists of resistors R, ~Rs, reset button Sl, timing time selection switch S2, capacitor C2 and island, and light-emitting diode I. ED
is composed of time base integrated circuit IC.
    The output control circuit is composed of transistor VT2, relay K, diode VD and AC contactor KM.
    After the AC 220v voltage is stepped down by G, rectified by UC, filtered by Cs and stabilized by vs, a DC 9v voltage (Vcc) is generated at both ends of C4, which is supplied
to VT1, VT2 and IC.
    The timer rhyme input terminal is connected to the audio output terminal of the electronic alarm clock. When the electronic alarm clock sounds (the piezoelectric ceramic piece BC sounds),
VT1 is saturated and turned on, causing the ② pin of IC to become low level , ③ pin outputs high level, VT2 is turned on, and the relay K is closed. The open contact is connected,
causing the AC contactor KM to close, and the motor (not shown in the circuit) is energized to work. At the same time, the IC enters the transient delay state; starts
timing.
    When the timing time ends (that is, the voltage at both ends of c3 rises to 2 Vx-/3), pin ③ of lC becomes low level, causing VT2 to cut off. K and KM
are released, and the motor is powered off and stops working.
    Sl is a manual reset button. When Sl is pressed, the ③ pin of lCl will output a high level , causing VT2 to conduct, and K and KM to pull in. During the conduction period of VT2
, the light-emitting diode LED lights up.
    S2 is the timing selector switch, which has three gears: 15rnin, 30min and 60min.
    (2) Without device parameter selection
    Ri-R6 all use 1/4W carbon film resistors.
    C- and G use polyester capacitors or monolithic capacitors; G uses polyester capacitors or CBB capacitors with a withstand voltage greater than 400V.
    VD uses 1N4007 silicon rectifier diode.
    LED uses +5mm light emitting diode.
    uc selects a 2A, 400V bridge rectifier.
    VT1 uses 59013 silicon NPN transistor; VT2 uses C8050 silicon NPN transistor.
    LC selects NE555 or 5G1555 time base integrated circuit.
    K chooses 9V DC relay.
    KM selects an AC contactor with a coil voltage of 220V, and its contact current capacity should be determined according to the actual power of the load.
    The selection of other components is shown in Figure 3-48, and there are no special requirements.
    (3) Timing controller circuit (4> as shown in Figure 3-48.