Three-phase motor forward and reverse control substitution circuit

Working principle of the circuit: Assuming that the control circuit of the three-phase motor of the large dough mixer is
damaged, the control circuit in the dotted box in the figure (made with three NE555) is used
to replace it . The original machine control panel is printed with a four-wire film and Control board connection,
the connection method of the three buttons is shown in Figure 2-3. The three control signals can only be set in the same way
, and the low level is effective here. The AC 14 V output from the original power supply transformer is rectified, filtered and
stabilized to supply power to the control circuit. IC . A monostable circuit is formed. After power on, the
47 kfl pull-up resistors on pins 2 and 6 are connected to vcc, so that the voltage at this point is higher than 2/3 Vcc, and the circuit is
in the 0 state. Relay K. No pull-in, normally closed contact K. . Supply 12 V to IC2 and
IC, and the green LED lights up, indicating that operation is possible. The original startup process
is omitted and the start key is set to the stop key. Icz and IC each constitute a bistable circuit.
After powering on, due to the pull-up and pull-down effects of the 47 kfl resistors on pins 2 and 6, pin 2 is higher than 1/3
Vcc, and pin 6 is lower than 2/3 Vcc. The two ICs All are in 0 state. When the forward key is pressed,
pin 2 of IC2 is connected to ground, and the circuit is triggered to flip to the l state. Although the button is lifted
and the voltage of pin 2 is high again, pin 6 always remains below 2/3 Vcc, and the circuit cannot flip
and remains in the l state. Pin 3 outputs high level to make K2 and K pull in, K,. When the contacts are closed, power is supplied to
the AC contactor KM to make it close, and the three sets of contacts turn L. ,￡:,厶three-phase power
is provided to the motor, and the motor runs in the forward direction. The K2 contact K2k of the pull-in shield
converts the reset pin 4 of IC3 from connecting to vcc to grounding and locks it in the reset state, so that IC
3 cannot be triggered before the forward rotation stops , which plays an interlocking role. To change the direction of operation, the stop button must be pressed first
. When the stop button is pressed, connect pins 2 and 6 of lC to the ground, and the circuit will be reversed from
state 0 to state l.