Motor speed control circuit having improved starting characteristics

A motor unit provided with a rotation speed control system, comprising first and second power supply terminals, a resistor having one end connected to said first power supply terminal, a constant voltage source having two terminals and generating a constant voltage between said two terminals thereof, one of said terminals of said constant voltage source being coupled to the other end of said resistor, a first voltage comparator having a first input terminal coupled to the other terminal of said constant voltage source and a second input terminal and generating an output in response to the difference between the voltage at said first and second input terminals, a motor coupled between said first power supply terminal and said second input terminal of said first voltage comparator, a current mirror circuit having a first output terminal coupled to said other end of said resistor and a second output terminal coupled to said second input terminal of said first voltage comparator, currents supplied to said resistor and said motor by said current mirror circuit being changed in response to said output of said first voltage comparator, a second voltage comparator comprising said voltage at said first input terminal with that at said second input terminal of said first voltage comparator and generating an output when the difference between said voltages at said first and second input terminals of said first voltage comparator is larger than a predetermined value, and means for enhancing the current derived from said first and second output terminals of said current mirror circuit in response to said output of said second voltage comparator.

A system comprising a power supply having first and second terminals, a motor having one end connected to said first power supply terminal, a resistor having one end connected to said first power supply terminal and having a resistance proportional to the internal resistance of said motor, a constant voltage source generating a constant voltage between its one and the other end and having a reference voltage terminal, said one end of said constant voltage source being connected to the other end of said resistor, a voltage comparator comparing the voltage at said other end of said constant voltage source with the voltage at the other end of said motor and generating an output in response to the difference between said voltages, a current mirror circuit having a first output terminal coupled to said other end of said resistor and a second output terminal coupled to said other end of said motor, currents supplied from said first and second output terminal of said current mirror circuit being changed in response to said output of said voltage comparator, a first transistor having a base coupled to said other end of said constant voltage source and an emitter connected to said other end of said motor, a second transistor having a base and a collector connected to the collector and emitter of said first transistor, respectively, a third transistor having a base connected to the base of said second transistor and an emitter coupled to the emitter of said second transistor through a first impedance element, a fourth transistor having a base coupled to said reference voltage terminal and an emitter coupled to said other end of said resistor through a second impedance element and a collector coupled to the output terminal of said voltage comparator, a fifth transistor having a base and a collector connected commonly to the base of said fourth transistor and an emitter coupled to said other end of said resitor through a third impedance element, said connecting point of the base and collector of said fifth transistor being also connected to the collector of said third transistor, a fourth impedance element inserted between said other end of said resistor and the bases of said fourth and fifth transistors, and means for supplying a current derived from the emitters of said second and third transistors to said current mirror circuit.