Abstract: In order to drive the stepper motor of a floppy disk drive with practically constant current in the face of fluctuations in supply voltage fed from a host system, a power control pulse generator circuit is provided which produces a series of power control pulses having a duty ratio dependent upon fluctuating supply voltage. The power control pulses are used for interrupting the excitation of the stepper motor windings during track seek operation. The power control pulses are generated by first repeatedly counting clock pulses from the host system to a predetermined number to provide periodically varying digital data, then translating the digital data into a triangular wave having an amplitude dependent upon the supply voltage, and then comparing the triangular wave with a reference voltage.

Abstract: This invention is regarded to a pulley of a belt drive mechanism. The belt drive mechanism is applied to, for example, magnetic disk apparatuses. The contact surface of the pulley, in contact with a belt of the belt drive mechanism, has a shape of a part of a surface of a sphere.A center of a sphere is at a point substantially the same as a point of intersection of a plane including a center line of an operating course of the belt and a center line of rotation of the pulley.

Abstract: A contour accentuation circuit for color signal comprises a variable gain amplifier, an output circuit and differential circuit. The output circuit outputs the signal according to the output signal from the variable gain amplifier and outputs the constant level signal to the output signal of amplitude level over predetermined level from the amplifier. The differential circuit differentiates the output signal from the output circuit and the amplifier amplifies and accentuates the contour of the input signal under the output control signal from the differential circuit.

Abstract: An AFC circuit using counters, flip-flops and logic gates produces a first pulse signal only when the phase of a VCO output signal lags the phase of a reference signal, and produces a second pulse signal only when the phase of the VCO output signal leads the phase of the reference signal. The first and second pulse signals control a switch to connect a first or a second constant current source to charge or discharge a filter circuit, to thereby produce a control voltage for the VCO. When the VCO output signal is in phase with the reference signal, the switch remains in a neutral position to hold a constant control voltage on the filter.

Abstract: An oscillation circuit for an integrated circuit device. The oscillation circuit includes a band-pass filter for producing an output signal having a voltage and a defined resonance frequency and a voltage to current converter type limiter amplifier connected to the band-pass filter for supplying a current to the band-pass filter corresponding to the voltage of the output signal of the band-pass filter.