Three-phase alternating current phase sequence detection circuit.

Figure 1 circuit is used to detect the three-phase alternating current phase sequence is correct. If the phase sequence is correct, then the circuit output signals to drive relay, three-phase electrical equipment connected to AC power; Otherwise, no power to protect the electrical equipment.
  The circuit mainly constituted a CD4013 dual D flip-flop. The three-phase AC buck, rectified pulse signal converted to low voltage input to the circuit A, B, C terminal, A, B both ends of the signal through the limiting resistor and zener diodes, reconstructive surgery, respectively, as the two D triggers control of the clock signal, C signal by the differential circuit terminal spikes into the role of the two trigger reset terminal R. If the phase sequence is correct, that is, A, B, C sequence of positive pulse appears, as shown in Figure 2 (a) shows, the first rising edge of A to the output Q1 high, then the rising edge of Q2 in the mechanism of a variable B high, the rising edge of the last C in the R-side spike generated by the two D flip-flop to reset, Q1, Q2 back to low, to complete a cycle. Three-phase alternating current is a periodic signal, Q2 output pulse frequency of the frequency and the same three-phase alternating current, the voltage of the DC component is C2 (22µF) capacitor voltage. The turn-on voltage of the transistor, relay electrical equipment connected three-phase power. If the phase sequence does not, then the output remains low Q2 unchanged, the transistor cut-off to ensure that the electrical equipment of the three-phase AC power is not connected. Points waveforms in Figure 2 (b) below.