Slew-rate control apparatus and methods for a power transistor to reduce voltage transients during inductive flyback

Abstract

Apparatus and methods that reduce the amount of conducted / radiated emissions from a power switch (200) when a transistor (210) is switched OFF are disclosed. In addition, apparatus and methods that reduce the slew rate in a power switch when the power switch is switched off are disclosed. The apparatus comprises a transistor (210) including an inductive load (230) coupled to the transistor, a plurality of current sources (222, 224) coupled to the gate of the transistor, and a clamp (250) coupled to either the gate and the drain of the transistor, or to the gate and to ground depending on the location of the inductive load, wherein the clamp comprises a resistive element (260) to increase the voltage of the clamp when current flows through the clamp, and wherein the increased voltage causes the apparatus to include a different slew rate.

Description

technical field

[0001] The present invention relates generally to semiconductor devices, and more particularly to power switches. Background technique

[0002] In a power switch, when a transistor driving an inductive load is turned off, the drain voltage of the transistor increases suddenly. Sudden changes in drain voltage usually cause conducted or radiated emissions on the output lines to the inductive load. Conducted and / or radiated emissions often cause interference in other electronic devices coupled to or in immediate proximity to the power switch, which can cause the overall system to perform less than expected.

[0003] Accordingly, there is a need to provide apparatus and methods that reduce the amount of conducted or radiated emissions from a power switch when the transistor is turned off. Additionally, it would be desirable to provide an apparatus and method for altering the transition time of the voltage in the power switch when the transistor is switched off....

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