Circuit for controlling the drive of motor

Claim 2

A circuit for controlling the running speed of a motor comprising; a comparator for comparing a speed signal produced responsive to the running speed of said motor with a reference signal, said comparator having substantially no offset; and a feedback amplifier including a differential amplifier for receiving an output signal from said comparator, an output circuit for feeding a drive current to said motor upon receipt of an output from said differential amplifier and a current feedback loop connected between said output circuit and said differential amplifier, said feedback amplifier having an offset, one end of said motor being directly connected to a first operating potential, another end of said motor being connected to a second operating potential through said output circuit and said current feedback loop, said drive current being based upon said offset of said feedback amplifier and flowing through the series path of said motor, said output circuit and said current feedback loop between said first operating potential and said second operating potential.

Claim 3

A circuit for controlling the running speed of a motor as set forth in claim 1, wherein said differential amplifier comprises; a first transistor and a second transistor connected in a differential from, of which the emitters being connected to an one end of a circuit of constant current supply via a first emitter resistor and a second emitter resistor, respectively, another end of said circuit of constant current supply being connected to said first operating potential; a third transistor and a fourth transistor of which the collectors are connected to the collectors of said first and second transistors, respectively; a third emitter resistor and a fourth resistor being respectively connected between said second operating potential and the emitters of said third and fourth transistors; and means for connecting the collector of said fourth transistor to the base thereof in order to form a current-mirror circuit by way of said third and fourth transistors; and said output circuit comprises Darlington-connected transistors; wherein the resistance of said first emitter resistor is different from the resistance of said second emitter resistor.

Claim 4

A circuit for controlling the running speed of a motor as set forth in claim 2, wherein said differential amplifier supplies a rated load current as a driving current to said motor when the potential difference between the potentials applied to the bases of said first and second transistors is zero.

Claim 5

A circuit for controlling the running speed of a motor as set forth in claim 2, wherein said fourth emitter resistor includes a resistance for negative feedback, and said resistance for negative feedback is coupled to said output circuit.