Timing control circuit (5)

(1) Introduction to circuit principle The timing time of this timing controller is adjustable in 7 levels (lOmui, 20min, 30rrun, 40min'50min, 60min and 90tnin) within the range of 10 to 90min . The timing controller can automatically cut off
the working power supply of the load (electric motor, electric heater and other electrical equipment) after the timing time is reached, which is safe, energy-saving, convenient and practical.
    The timing controller circuit is composed of a power supply voltage stabilizing circuit, a timing time selection circuit, a delay circuit, and a Schmitt trigger control circuit.
    The power supply voltage stabilizing circuit consists of the start button S1, power transformer T, bridge rectifier uc, filter capacitor C, and i-side voltage stabilizing integrated circuit IC1
.
    The timing time selection circuit is composed of selection switch S2 and resistor ~R7.
    The delay circuit consists of capacitors G, B, and resistors R9, R. , the normally closed contacts K3 and D4 of the relay K are composed of the NOT gate integrated circuit IC2 (D1~D4)
.
    The Schmitt trigger control circuit is composed of transistors VT1, VT2, resistors Ri~R16 and diode VD.
    After selecting the timing time, press the start button Sl. After the AC 220V voltage is stepped down by T, rectified by UC, filtered by G and stabilized by lcl,
a _r-12V voltage is generated and supplied to the relevant circuits.
    After IC2 is powered on, its internal NOT gate circuit D4 outputs a low level, causing VT1 to cut off. VT2 is saturated and conductive, the relay K is closed, and
its normally open contacts Kl and K2 are connected, so that the power supply is locked and turned on (after releasing Sl, the AC power supply remains on), and the AC contactor KM is closed
, so that The load is powered on. At the same time, the +12V voltage charges the capacitor G through the timing time selection circuit, and the circuit starts timing.
    When the timing time is over, the output end of the NOT gate D4 becomes high level, causing VT1 to conduct, VT2 to cut off, K is released, its normally open contacts
K1 and K2 are disconnected, and the timing controller stops working; at the same time, KM is released, The load also stops working when the power is cut off.