Abstract: A power supply circuit for a control circuit of a motor having an armature, includes a first power supply branch having a series combination of a first resistor, a first diode and a Zener diode connected between a supply of power and a reference potential, with a first junction between the first diode and the Zener diode constituting an output of the first power supply branch which supplies a fixed first current; and a power supply second branch having a series combination of a second resistor, a second diode and a capacitive element connected between the armature of the motor and the reference potential, such that a variable second current in correspondence with current provided by the armature of the motor is provided at a second junction between the second diode and the capacitive circuit, and combined with the first current thereof for supply to the control circuit.

Abstract: A safety module for a motor speed control circuit, when speed control circuit has a failure mode in which full power is applied to the motor being driven by the speed control circuit. The safety module has a high pass filter coupled to a variable voltage power output of the speed control circuit, and a threshold member coupled to an output of the high pass filter for passing a signal only if a change in the signal exceeds a predetermined value. A semiconductor short-circuiting switching device is coupled to the threshold device and is also coupled to the power terminals of the motor and to the output of the speed control circuit for shorting out the output of the speed control circuit responsive to an abrupt increase in a signal at the output of the speed control circuit which exceeds the predetermined value at the output of the speed control circuit.

Abstract: In accordance with a first embodiment of the invention, line dropout protection is provided for a d.c. motor wherein motor operation is prevented if power is applied at the time a main speed control device is not set in a zero position. Re-enabling motor operation is simply provided by resetting the motor speed control device to a zero position and reapplying power.In accordance with the second embodiment of the invention, line dropout protection is provided for a d.c. motor wherein predetermined excess motor acceleration is prevented when power is applied to the d.c. motor. The instant invention prevents motor start-up under unexpected conditions, thereby clearly enhancing safety during operation of any device controlled by the d.c. motor.

Abstract: A current limiting control circuit for a d.c. motor, wherein compensation is provided for the inherent voltage drop across the armature of the d.c. motor with a first dedicated amplifier, while a second dedicated amplifier provides current limit control. In providing a separate and dedicated amplifier for the current limiting function, the limitations inherent in the current/resistance compensation circuit, such as lag in response time, are avoided.

Abstract: An anti-plug reversing circuit for use with a variable speed D.C. motor which provides safe and fast motor reversing with dynamic braking. The circuit, by sensing counter-EMF, prevents the premature application of a voltage of opposite (reversing) polarity until the motor armature has come to a full stop. The circuit advantageously utilizes a three-wire control input, is low cost, easily manufactured and applicable for use with low cost D.C. motors.