Abstract: 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.

Abstract: A digitally controlled switchmode power supply by the use of a pulse width modulated (PWM) controlled field effect transistor, switches an inductor between input and output sides to provide a controllable DC output voltage. The digital processor receives and digitizes the input and output voltages and also the current through the associated inductor and derives a PWM control loop signal driving the associated field effect switching device to switch the inductor. The foregoing compensates for nonlinear changes in the value of the inductance due to changes in inductor currents and also avoids resonance at pole points of the LC circuit in the power supply. In addition a change in buck to boost modes may be accomplished automatically depending on input voltage operating conditions.

Abstract: An optical recording system having a DC restored read signal for qualifying pulses in the read channel. The equalized and filtered read signal is input to a differentiator and a DC restore circuit. The zero crossings of the differentiated signal which represent the peaks of the pulses are detected. The DC restore circuit inverts the read signal, generates a reference voltage, and compares the negative pulses peaks of the read signal to the reference voltage. The charge of a capacitor is adjusted according to the difference in voltages of the pulse peaks to that of the reference voltage in order to maintain a constant DC level. The DC restored signal is qualified according to a threshold. Only those pulses which have zero crossings and which have been qualified are considered to be valid.