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Transistor Driver Inner Feedback Loop

IP.com Disclosure Number: IPCOM000040231D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Commander, RD: AUTHOR

Abstract

A previous article [*] describes a transistor bridge driver with balance control for driving an inductive load. In the present article, an additional inner feedback loop with low gain and high bandwidth is additionally employed to reduce transient crossover distortion in the load current. The earlier article describes a linear transistor bridge driver circuit with a second feedback path to ensure that the bridge transistors turn on equally despite component variations. A first feedback path senses the voltage across resistors in opposite arms of the bridge to provide current feedback to the input. The second feedback path uses voltage feedback from the load to ensure that the driving pair of transistors turn on equally.

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Transistor Driver Inner Feedback Loop

A previous article [*] describes a transistor bridge driver with balance control for driving an inductive load. In the present article, an additional inner feedback loop with low gain and high bandwidth is additionally employed to reduce transient crossover distortion in the load current. The earlier article describes a linear transistor bridge driver circuit with a second feedback path to ensure that the bridge transistors turn on equally despite component variations. A first feedback path senses the voltage across resistors in opposite arms of the bridge to provide current feedback to the input. The second feedback path uses voltage feedback from the load to ensure that the driving pair of transistors turn on equally. The wide availability of power FETs makes it now possible to build linear power amplifiers of higher bandwidth than with bipolar power transistors. To avoid excessive dissipation in such amplifiers, class B output stages are commonly used. Because of tolerances associated with the bias circuitry, such output stages will commonly have a deadband - i.e., their gain drops to zero briefly as the output signal drive commutates from one driver to the other. Typically, such an output stage has a high gain feedback loop around it which removes most of the distortion associated with the deadband. However, the high gain feedback loop normally includes a low-pass filter to stabilize it, which means that the class B outpu...