Hold-up time enhancement circuit for llc resonant converter

Abstract

An open loop half-bridge LLC power converter includes circuitry to reliably increase hold-up time without sacrificing efficiency. An LLC resonant circuit includes resonant inductance, a primary transformer winding, and resonant capacitance. An auxiliary circuit includes an auxiliary transformer winding, an inductor, and a third switching element coupled in series. A controller is coupled across a voltage sensor and effective thereby to determine a holdup time condition. In a “normal” operating condition the controller generates switch driver signals to turn OFF the third switching element and disable the auxiliary circuit, and in a hold-up time condition the controller turns ON the third switching element and enables the auxiliary circuit wherein the output voltage is increased via current supplied from the auxiliary winding. In various embodiments the auxiliary winding may be an auxiliary primary or secondary, or a secondary to an auxiliary primary winding of a second transformer.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application claims benefit of the following patent application(s) which is / are hereby incorporated by reference: U.S. Provisional Application No. 61 / 622,862 dated Apr. 11, 2012.[0002]A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.BACKGROUND OF THE INVENTION[0003]The present invention relates generally to power converters. More particularly, the present invention relates to gain enhancement circuitry for LLC resonant power converters wherein a hold-up time may be increased with minimal effect on efficiency.[0004]As market requirements for high efficiency have become more demanding, LLC resonant converters have correspondingly grown in p...

AI Technical Summary

Benefits of technology

The present invention is about a half-bridge LLC resonant power converter that can increase its hold-up time without adding extra bulk capacitance or sacrificing efficiency. Auxiliary circuitry is used to increase the gain of the converter and maintain the output voltage, even at lower bulk voltages. This results in better performance without the need for a larger, more expensive bulk capacitor.

Problems solved by technology

However, there is a trade-off between the high efficiency and long hold-up time performance in a resonant converter.

However, the hold-up time will consequently decrease by a significant amount as well.

However, this results in problems of low power density and also higher cost.

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