Hold-up time enhancement circuit for LLC resonant converter

摘要

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.

主权项

1. A power conversion system comprising: first and second switching elements coupled in series across first and second power input terminals; an LLC resonant circuit coupled between the first and second switching elements and comprising a first inductor, a primary winding of a transformer, and one or more resonant capacitors; an output circuit comprising one or more secondary transformer windings and a bulk capacitor coupled across first and second output terminals; a voltage sensor; a hold-up time enhancement circuit comprising an auxiliary primary winding of the transformer, a second inductor coupled on a first end to the auxiliary primary winding, and a third switching element coupled to a second end of the second inductor; a controller coupled to the voltage sensor and effective to determine a hold-up time condition based on a voltage across the voltage sensor; wherein the controller is further effective in a first operating mode associated with a normal condition to generate switch driver signals to turn OFF the third switching element and disable the hold-up time enhancement circuit; and the controller is further effective in a second operating mode associated with a hold-up time condition to generate switch driver signals to turn ON the third switching element and enable the hold-up time enhancement circuit wherein an output voltage across the first and second output terminals is increased via current supplied from the auxiliary primary winding.