Design of three-phase AC phase sequence detector circuit

　　When using a three-phase AC motor, you need to know the phase sequence of the connected three-phase power supply. If the phase sequence is incorrect, the motor's rotation direction will be opposite to the required direction, which may lead to safety accidents. The function of this circuit is to detect the phase sequence of the three-phase AC power supply and automatically connect the load if the phase sequence is correct. If it is incorrect, the load will not work.

　　Working principle of the circuit: After the three-phase AC is stepped down and rectified, it is connected to the three terminals A, B, and C respectively. The two ends A and B are respectively limited and shaped by resistors R1, R2 and voltage-stabilizing diodes VS1, VS2 and sent to the two clock pulse signal terminals of the IC integrated circuit. If the phase sequence is correct (i.e., positive pulses appear in sequence in the three phases A, B, and C), the 1st and 13th pins of the IC integrated circuit both output high levels, making VT1 and VT2 conduct, the coil of relay K energized, the moving contact of K closed, and the electrical equipment starts to work. At this time, the C terminal outputs a reset signal to the reset terminal of the IC integrated circuit through resistor R3 and voltage-stabilizing diode VS3, and the 1st and 13th pins output low levels. Since the capacitor C2 begins to discharge, the transistors VT1 and VT2 continue to conduct to maintain the relay to continue to be energized, and the load works normally, completing the change of one cycle of the three-phase AC. If the phase sequence is wrong, the 13th foot will maintain a low level, the transistors VT1 and VT2 will be turned off, the coil of relay K will lose power, the make contact of K will be disconnected, and the electrical equipment will stop working (the function table of the dual D flip-flop is shown in the attached table). The transistors VT1 and VT2 are S9013 silicon NPN transistors; IC is CD4013 dual D flip-flop integrated circuit; K is JRX-13F 12V DC relay; there are no special requirements for other components, which can be selected according to the markings on the figure.