Linear Technology Corporation

National Semiconductor Corporation

Dale R Eagar

Joseph V DeNicholas

John L Seago

A system includes a first transistor configured to control a current through one or more LEDs and an inductor coupled in series with the one or more LEDs. The system also includes a current mode switcher configured to control the first transistor so that the inductor has a substantially constant ripple current. The system may further include a resistor and a second transistor coupled across the one or more LEDs and an integrating capacitor coupled in series with the second transistor. The switcher may include a driver configured to drive the first transistor to turn the first transistor on and off. The switcher may also include a detector configured to turn off the first transistor when a current through the first transistor exceeds a first threshold. The switcher may further include a timer configured to turn on the first transistor when a voltage on the integrating capacitor exceeds a second threshold.

Current mode switcher having novel switch mode control topology and related method

A switch recovery circuit is disclosed for improving the efficiency of switching voltage regulators. The switch recovery circuit includes a first and second inductor, a capacitor, a first diode, and a recovery circuit. The capacitor and diode comprise an AC coupled loop circuit around the first inductor. Current flows through the loop circuit soon after the switch is opened and charges the capacitor. The recovery circuit, which includes a second inductor that is magnetically coupled to the first inductor, provides current, at least some of which discharges the capacitor (i.e. current that flows in the opposite direction to the loop current) after the loop current stops. A second diode is interposed in series with the second inductor to provide appropriate voltage offsets in the circuit and to prevent the first inductor from being shorted to ground through the second inductor.

Systems and methods for conserving energy in a switching circuit

The present invention provide systems and methods for reducing a reverse recovery current through a body diode in a synchronous switching transistor. An inductor is coupled in the commutation path of the body diode of the synchronous switching transistor. The inductor slows the rate of increase of the reverse recovery current to reduce avalanche effects in the synchronous switching transistor. This reduces the peak reverse recovery current through the body diode of the synchronous switching transistor when the body diode commutates, thereby reducing power dissipation in the main switching transistor. An inductor may be coupled to both switching transistors so that power dissipation is reduced if the regulator is operated as a buck or boost regulator. A diode and a reverse recovery switcher may be coupled to the inductor to transfer energy in the inductor back to the input or output capacitor after the body diode commutates.

Systems and methods for controlling the charge profile during the commutation event of a synchronous switching transistor in a regulator

Recovery systems and methods of the present invention include circuitry that transfers energy from an input to an output with reduced power dissipation. A synchronous switching regulator is one application for the recovery system of the present invention. An inductor may be used in a synchronous switching regulator to reduce power dissipation caused by reverse recovery current that flows through the body diode of the synchronous switching transistor when the synchronous switching transistor turns OFF. Energy in the inductor may be transferred back to the input or output capacitor of the switching regulator through a recovery system of the present invention. The recovery circuit of the present invention provides an efficient method for intercepting energy in the inductor, and presenting power to a recovery switcher in a manner that allows the recovery switcher to transfer the energy into the input or output capacitor of the switching regulator efficiently.

Circuitry for improving the efficiency of a switching regulator by reducing reverse recovery current

A switching regulator that actively snubs waveforms is provided. The switching regulator includes an inductor, a power switch electrically coupled to the inductor, a first diode electrically coupled to the inductor, and a snubber circuit being coupled in parallel to the inductor. The power switch and the snubber circuit include break-before-make switches such that the power switch is closed only after the snubber switch is opened to initiate a switching cycle, and the snubber switch is closed only after the power switch is opened to provide a decay path for snubbing ringing waveforms.

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Black Forest, CO, United States of America

Dale R Eagar