Three-phase motor phase failure transistor protection circuit

 (1) The circuit consists of magnetic ring L1-L3, diodes VD1-VDe, capacitors G~G and transistors VT1-VT3 to form
a phase failure signal sampling circuit. VT1-VT3 form an inverter, and its output is connected in parallel through diodes VD4~VD6 to form an OR gate circuit. VT4 and
VT5 form a transistor relay.
    (2) Normal operation When the motor works normally, the induced electromotive force on TA1, TA2 and TA3 is rectified by VD1~VD3. G~G
filtering makes _VT1-VT3 saturated and conductive, and its collector output potential is "O". For the OR gate composed of VD4-VD6, the inputs are all
low potential "o", so that the output is low potential "O", causing VT4 to be cut off, VT5 to be saturated and conductive, and the intermediate relay KA is electrically closed, and its normally open
The contacts are reunited and the motor operates normally.
    (3) Phase failure protection function When a phase failure occurs, for example, the L3 phase is disconnected, the induced electromotive force on L3 is zero, causing VT3 to cut off, and its
collector outputs a high potential of "1", so the OR gates VD4~VD6 output high The potential is "1", causing VT4 to be saturated and conductive, and VT5 to be cut off. KA loses power
and is released. Its normally open contact is disconnected, causing the contactor KM to lose power and release, cutting off the power supply of the motor, and the motor M stops.