Anti-stall motor drive
First Claim
1. An anti-stall motor drive circuit for a very slow running permanent magnet d.c. motor comprising:
- a drive transistor having collector, base and emitter electrodes, said motor being connected to the collector of said drive transistor and a current limiting resistor being connected to the emitter of said drive transistor;
means for detecting a stalled condition of said motor; and
means responsive to said detecting means for momentarily increasing a base drive voltage to said transistor to momentarily increase the voltage across said motor an order of magnitude greater than normal opertating voltage and exceeding a rated voltage of the motor to overcome the stalled condition.
3 Assignments
0 Petitions
Accused Products
Abstract
An anti-stall motor drive circuit for a very slow running permanent magnet d.c. motor is disclosed. The slow running speed of the motor sometimes allows an insulating film to build up between the brushes and the commutator which causes the stalled condition. The motor (10) is connected in the collector circuit of a drive transistor (Q1) which has a current limiting resistor (R9) connected in its emitter circuit. A stalled condition of the motor (10) is sensed by a lack of output from a tachometer (16) output. The output of the tachometer is full wave rectified by an operational amplifier (22) and diodes (CR1 and CR2). The rectified tachometer voltage is applied to an integrator (24 and C1) having a clamping diode (CR7) connected in its feedback circuit. A zero output from the rectifier allows the integrator output to ramp up to a limiting value determined by the clamping diode. The output of the integrator is applied to the base of the drive transistor to cause a voltage approximately fifteen times that of normal operating voltage to be impressed across the motor. This "jolt", which is twice the rated voltage of the motor, overcomes the stalled condition and burns off any insulating film which may have developed between the commutator and the brushes.
39 Citations
4 Claims
-
1. An anti-stall motor drive circuit for a very slow running permanent magnet d.c. motor comprising:
-
a drive transistor having collector, base and emitter electrodes, said motor being connected to the collector of said drive transistor and a current limiting resistor being connected to the emitter of said drive transistor; means for detecting a stalled condition of said motor; and means responsive to said detecting means for momentarily increasing a base drive voltage to said transistor to momentarily increase the voltage across said motor an order of magnitude greater than normal opertating voltage and exceeding a rated voltage of the motor to overcome the stalled condition. - View Dependent Claims (2, 3, 4)
-
Specification