Hold-up time enhancement circuit for llc resonant converter

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 sensing circuit;
• a hold-up time enhancement circuit further comprising an auxiliary secondary winding of the transformer, a second inductor coupled on a first end to the auxiliary transformer winding, and a third switching element coupled to a second end of the second inductor;
• and
• a controller coupled to the voltage sensor and effective to determine a holdup time condition based on a voltage across the voltage sensor,
• 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 holdup time enhancement circuit wherein the output voltage is increased via current supplied from the auxiliary winding.

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 first transformer, and one or more resonant capacitors;
• a primary winding of a second transformer coupled in parallel with the primary winding of the first transformer;
• an output circuit comprising one or more secondary transformer windings of the first transformer and a bulk capacitor coupled across first and second output terminals;
• a voltage sensor;
• a hold-up time enhancement circuit further comprising a secondary winding of the second transformer as an auxiliary winding, a second inductor coupled on a first end to the auxiliary winding, and a third switching element coupled to a second end of the second inductor;
• and
• a controller coupled to the voltage sensor and effective to determine a holdup time condition based on a voltage across the voltage sensor,
• 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 holdup time enhancement circuit wherein the output voltage is increased via current supplied from the auxiliary winding.