Micro Linear Corporation

Daniel D Culmer

Mark R Vitunic

John E DeFiore

A circuit for powering a two-phase AC induction motor. The circuit generates a first signal of the form Vdc+A sin(2.pi.ft-0.degree.) and a second signal of the form Vdc+A sin(2.pi.ft-90.degree.). The first signal is input to a first error amplifier along with a first sampled difference signal from the motor. The second signal is input to a second error amplifier along with a second sampled difference signal from the motor. The outputs from each of the first and second amplifiers is input into a first comparator and a second comparator along with a sawtooth waveform to create a first sinusoidally modulated square wave signal and a second sinusoidally modulated square wave signal. The first and second sinusoidally modulated square wave signals are fed to driver circuits which in turn control an H-bridge circuit for powering the motor from a DC bus.

Variable speed AC induction motor controller

A signal generator generates a reference signal, centered about a reference voltage and having a predetermined period. The signal generator also generates output signals P and Z. The output signal P is a squarewave which changes levels at the peaks of the reference signal. The output signal Z is a squarewave which changes levels at the reference voltage crossings of the reference signal. A phase-shifted signal generator generates a phase-shifted signal using the output signals P and Z by switching in appropriate signal levels from the signal generator. The output signals P and Z are input to a switch control circuit which controls a network of switches, depending on a current region of the reference signal, to couple appropriate signals to an amplifier circuit. The switch control circuit determines the current region based on the state of the output signals P and Z. The amplifier circuit provides the phase-shifted signal in response to the signals coupled to it by the network of switches. In an alternate embodiment, the output signal Z is generated by a hysteretic comparator and changes levels at positive and negative threshold levels above and below the reference voltage. The values of the positive and negative threshold values are variable and determine the degree of phase shift between the phase-shifted signal and the reference signal.

Phase-shifted triangle wave generator

The invention employs an active element, a p-channel MOSFET, between a regulated voltage and a SCSI terminating line. An 'ideal' current source terminator is most effective when a signal line is negated (low-to-high transition), whereas a resistive terminator is most effective when a signal line is asserted (high-to-low transition). The I-V characteristics of a p-channel MOSFET, wherein the relationship between the termination voltage and the termination current is characterized by a nonlinear and smooth voltage versus current curve, provide an optimized transient response for signal negations and signal assertions on a SCSI bus.

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San Jose, CA, United States of America

Daniel D Culmer