This invention relates to circuitry for motor control and more particularly to a motor control circuit which will cause a DC motor to run in much the same manner as a synchronous motor.
A synschronous motor is one which will run at a constant speed regardless of the load torque requirements. This is true only up to a certain point, however, and when load torque requirements exceed the capability of the motor, it drops out of synchronization and begins to slow down. Synchronous motors are used in devices which must run at constant speeds such as clocks, tape recorders, and the like. There is a class of alternating current (AC) motors which inherently operate synchronously and such motors require no external circuitry to achieve synchronous operation. However such motors require an AC source for operation, and sometimes only a DC source is available. A DC motor will not operate synchronously without some external circuitry to detect its speed and vary the current to the motor accordingly. According to the present invention a circuit is provided which causes a DC motor to operate synchronously.