Symbol Technologies, LLC

Media Vision

Michael S Rovner

Bryan J Colvin, Sr

An audio power amplifier is provided that includes circuitry to prevent popping noises when the amplifier is turned on and turned off. The amplifier can be powered with a single-ended voltage power supply, and thus may be used within systems such as personal computer. The amplifier includes a control circuit that prevents the fast charging of the output AC coupling capacitor when the amplifier is turned on and turned off. The control circuit controls a driver stage such that the output transistors turn on slowly when power is first applied, and such that the output transistors turn off quickly when the supply voltage is removed.

Audio power amplifier with noise prevention at turn-on and turn-off

A voltage drive circuit for driving a stepping motor for a laser scanning mirror in a laser bar code reader assembly. The voltage drive circuit provides a highly damped, low q drive in which resonance is virtually eliminated and wherein damping of the rotor is proportional to its angular velocity, and also the position of the rotor precisely follows an input voltage signal driving the motor. The stepping motor includes a rotor, a stator, a center-tapped AC winding and a DC winding. The motor drive circuit comprises a triangular waveform generator for generating a periodic triangular voltage signal. A driving circuit for an AC winding receives the periodic triangular voltage signal as an input, and includes a voltage feedback circuit in which the voltage across the AC winding is compared with and caused to follow the input voltage signal driving the AC winding. The drive circuit for the AC winding includes a first noninverting operational amplifier and a second inverting operational amplifier for driving respectively first and second phase sides of the AC winding. Each of the first and second operational amplifiers receive the triangular voltage signal as a first input signal and also receives as a second input a feedback signal representing respectively the voltage across the first and second phase sides of the AC winding. A drive circuit for the DC winding utilizes a voltage feedback signal obtained from the AC winding for compensating for an angular offset between the AC and DC windings.

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San Jose, CA, United States of America

Michael S Rovner