Abstract: An a.c. switch has two pairs of diodes each of which has two diodes connected in back-to-back relationship between the signal input and output of the switch. The two pairs of diodes are connected in parallel with each other in opposite senses. A MOSFET transistor is connected between the junctions of the two diodes in each pair. A switching control unit controls switching of the transistor such that, when the transistor is conducting, signal current flows between the input and output via one diode in one pair, the transistor, and one diode in the other pair. When the transistor is not conducting, current flow between the input and output is blocked.

Abstract: A control system for a three-phase motor has two triac switches connected in respective supply lines to the motor. Both switches are initially closed so that power is supplied to the motor on all three lines. After a predetermined time, when the motor has reached its operating speed, one switch is opened by a logic unit so that single phase power is supplied to the motor on two lines. One of the switches is subsequently periodically closed for short intervals, and the other switch is periodically opened for short intervals under control of a monostable unit, so as to produce hunting of the motor. Hunting of the motor is detected by a speed monitor responsive to the counter EMF of the motor. The system has a phase detector responsive to the phase relationship between signals on the supply lines which prevents the switches being closed if there is not the desired phase relationship between the signals.

Abstract: A control circuit is connected between a three-phase power supply and a motor and ensures the correct application of phase signals to the motor, regardless of the way in which the control circuit is connected to the power supply. A first output signal of the supply is connected directly to an input of the motor via the circuit. Supply of power to the other two inputs is controlled by four switches, two of which receive signals from the second supply output and have their outputs connected to respective motor inputs, and the other two of which receive signals from the third supply output and have their outputs connected to respective motor inputs. The switches are controlled such that two switches are on, and the other two switches are off if the third output signal is positive with respect to the first output signal when the second signal passes through zero with respect to the first signal in a positive sense.

Abstract: A gyroscope motor control system has a phase-locked loop circuit and an antihunting circuit. The phase-locked loop circuit has a voltage-controlled oscillator which produces the drive signal for the motor. The frequency of the oscillator is controlled by the output of a phase discriminator which is in turn dependent on the difference in phase between a reference frequency and a feedback signal from the motor drive signal. A capacitive pick-off senses the speed of rotation of the gyroscope inertia wheel and a signal in response to this speed is supplied to a directional phase discriminator together with the feedback signal. The output of the discriminator varies with change in phase difference between its two inputs, and is supplied via a switching transistor to the input of the oscillator to effect minor variations in its frequency such as to reduce fluctuations in motor speed. The transistor is held off until there is substantial synchronism with the motor drive signal and the inertia wheel speed.