| 摘要 |
<p>Safety device is fitted to the drive control circuit of a domestic laundry washing machine; the permanent magnet motor being fed by a rectified current with cyclical commutation, which is variable by thyristors. The triggers of the thyristors are connected to a relaxing circuit formed by a time constant network, working with two transistors of complementary polarities arranged head to tail. A circuit known as a "diode pump" is located between the base of the transistor connected to the time constant network, and a common conductor feeding pulsed current, connected to one of the motor terminals. This circuit is shunted by an electronic interrupter, the control electrode of which is connected to the other terminal of the motor. The electronic interrupter is a transistor in the emitter of which a zener diode is inserted; the emitter forming the control electrode of the interrupter. The base of the interrupter-transistor is connected through a resistance to the common feed of pulsed current for the control circuit. The capacitor of the diode pump circuit is shunted by a resistance. Used to protect the motor against burning out, in the event, say, of the door not having seen fastened correctly, and opening to allow items from inside to become trapped and block the motion of the drum. The induction current is then reduced immediately to a safe level, and this is achieved at comparatively little expense relatively to the motor control circuit. Protection can thus be extended to machines at the cheaper end of the market.</p> |
