Resonant converter with dual-mode control
It may be desirable to limit the switching frequency of a pulse frequency modulated (PFM) resonant converter, however certain load conditions and/or startup condition require high switching frequencies to regulate an output voltage. The disclosed resonant converter can limit a maximum switching frequency while regulating an output voltage by shifting from PFM to phase-difference modulation based on a load condition. The appropriate modulation can be applied based on a comparison between a charge-control signal and a load-control signal.
1 . A method for controlling switching of a full bridge switching network of a resonant converter, the method including:
assessing a charge-control signal criterion that is satisfied when a charge-control signal is greater than or equal to a load-control signal;
changing states of first totem pole switching signals for the full bridge switching network when the charge-control signal criterion is satisfied;
assessing a first clock-timer signal criterion that is satisfied when a first clock-timer signal is greater than or equal to a minimum switching period signal; and
maintaining states of second totem pole switching signals for the full bridge switching network until both the charge-control signal criterion and the first clock-timer signal criterion are satisfied, thereby clamping a switching frequency of the first totem pole switching signals and the second totem pole switching signals at a target frequency defined by the minimum switching period signal.
2 . The method according to claim 1 , wherein maintaining states of the second totem pole switching signals for the full bridge switching network until both the charge-control signal criterion and the first clock-timer signal criterion are satisfied results in a phase difference between the first totem pole switching signals and the second totem pole switching signals when the charge-control signal criterion is satisfied before the first clock-timer signal criterion is satisfied.
3 . The method according to claim 2 , wherein the phase difference reduces a power injection period of the full bridge switching network.
4 . The method according to claim 2 , wherein maintaining states of the second totem pole switching signals for the full bridge switching network until both the charge-control signal criterion and the first clock-timer signal criterion are satisfied results in no phase difference between the first totem pole switching signals and the second totem pole switching signals when the charge-control signal criterion is satisfied after the first clock-timer signal criterion is satisfied.
5 . A method for controlling switching of a switching network of a resonant converter, the method including:
generating a charge-control signal corresponding to a charge of a resonant network of the resonant converter;
generating a load-control signal based on a voltage reference and an output from a rectifier network of the resonant converter;
providing the charge-control signal and the load-control signal as feedback to a switching controller of the resonant converter; and
providing switching signals from the switching controller to a first totem pole circuit and a second totem pole circuit of the resonant converter based on a control mode of the resonant converter, wherein the control mode includes:
assessing a charge-control signal criterion that is satisfied when the charge-control signal is greater than or equal to the load-control signal;
changing states of the switching signals for the first totem pole circuit when the charge-control signal criterion is satisfied;
assessing a first clock-timer signal criterion that is satisfied when a first clock-timer signal is greater than or equal to a minimum switching period signal; and
maintaining states of the switching signals for the second totem pole circuit until both the charge-control signal criterion and the first clock-timer signal criterion are satisfied, thereby clamping a switching frequency of the switching signals at a target frequency defined by the minimum switching period signal.
6 . The method of claim 5 , wherein generating the charge-control signal comprises:
generating the charge-control signal by sensing a current of the resonant network;
integrating the current to obtain the charge; and
providing the charge as a charge-control feedback signal to the switching controller.
7 . The method of claim 6 , wherein generating the charge-control signal is performed while the resonant network is coupled to an integrator circuit.
8 . The method of claim 5 , wherein the resonant network comprises an LLC resonant network, and wherein generating the charge-control signal comprises:
detecting a voltage across a series capacitor of the LLC resonant network.
9 . A non-transitory computer-readable medium storing instructions which, when executed by a processor, cause the processor to perform a method for controlling switching of a full bridge switching network of a resonant converter, the method including:
assessing a charge-control signal criterion that is satisfied when a charge-control signal is greater than or equal to a load-control signal;
changing states of first totem pole switching signals for the full bridge switching network when the charge-control signal criterion is satisfied;
assessing a first clock-timer signal criterion, wherein the first clock-timer signal criterion is satisfied when a first clock-timer signal is greater than or equal to a minimum switching period signal; and
maintaining states of second totem pole switching signals for the full bridge switching network until both the charge-control signal criterion and the first clock-timer signal criterion are satisfied, thereby clamping a switching frequency of the first totem pole switching signals and the second totem pole switching signals at a target frequency defined by the minimum switching period signal.
10 . The non-transitory computer-readable medium of claim 9 , wherein maintaining the states comprises modulating a phase difference between the first totem pole switching signals and the second totem pole switching signals, after clamping the switching frequency.
11 . The non-transitory computer-readable medium of claim 10 , wherein the phase difference reduces a power injection period of the full bridge switching network.