Sequential power-on control circuit

Circuit working principle: The power supply part of this circuit consists of power transformer, bridge
rectifier and ripple bypass capacitor. After the 50 Hz, 220 V AC power
is stepped down, rectified and filtered by transformer T, a pulsating DC voltage is output for use by the control circuit
.
    The CD4017 (lC) in the picture is a 5-level Johnson decimal counter chip.
It has a total of 10 output terminals, of which only 4 are used in this article. The flashing LED clocks the decade
counter. After closing S and turning on the circuit, all four output terminals of the IC Q. , Q3, Qs and Q7 become high one by one at the clock interval of Is, causing the thyristors vS, ~ VS4 to conduct in sequence and drive the corresponding relay K. One K4. Xs, ~ XS4 are 4 power sockets on the power distribution board, respectively connected to 4 electrical devices . When S is turned on, since the four sockets must obtain power through their respective relays, the four electrical devices are turned on one by one at the clock interval of Is.