Method and circuit for peak power in quasi-resonant converters
Implementations of the present disclosure involve a circuit and/or method for a control circuit of a switched-mode power supply that allows the power supply circuit to temporarily provide up to 2.0× the nominal maximum power rating of the circuit without the need for large storage devices within the power supply. For example, a control circuit of a switched-mode power supply may cause the power supply to operate in a quasi-resonant mode. However, when the load on the circuit increases such that the feedback voltage measurement meets or exceeds a voltage threshold, the control circuit causes the switched-mode power supply to enter a power excursion mode with a fixed switching frequency. If the load on the switched-mode power supply continues to increase, the off time of the switched-mode power supply may be scaled in response to increase the power provided by the switched-mode power supply.
1. A method for forming a power supply circuit comprising:
configuring the power supply circuit to control a duty cycle of a switch to operate the switch in an on-state or an off-state to control power delivered to a load;
configuring a first circuit to determine a first off-time duration of the switch in response to a first condition of the load;
configuring a second circuit to detect a peak power excursion condition of the power supply circuit;
configuring the first circuit to set a switching frequency of the switch to have an off-time of substantially the first off-time duration in response to the peak power excursion condition; and
configuring the first circuit to adjust the first off-time duration by a scaling factor in response to a change in load condition during the peak power excursion condition.
2. The method of claim 1 further including configuring the first circuit to include a counter circuit to determine the first off-time duration for each cycle during the first condition of the load.
3. The method of claim 2 including configuring the first circuit to include a storage circuit for storing the first off-time duration.
4. The method of claim 1 wherein configuring the first circuit to adjust the first off-time duration includes forming the scaling factor inversely proportional to a feedback signal that is representative of a power delivered to the load.
5. The method of claim 1 wherein configuring the first circuit to adjust the first off-time duration includes forming the scaling factor directly proportional to a feedback signal that is representative of a power delivered to the load.
6. The method of claim 1 further including configuring the power supply circuit to operate in a quasi-resonant operating mode in response to the first condition of the load.
7. The method of claim 1 further including configuring the power supply circuit to operate in a continuous conduction operating mode for at least a portion of the peak power excursion condition.
8. A power supply circuit comprising:
a switching circuit for operating the power supply circuit in an on-state or an off-state and alternate between the on-state and the off-state at a switching frequency to control power delivered to a load;
a first circuit for determining a first duration of a particular off-state during a first condition of the load;
a peak power excursion detection circuit to detect the load increasing to no less than a peak power excursion threshold; and
a second circuit configured to form an off-time duration of the off-state as one of substantially the first duration in response to detecting the load increasing to substantially the peak power excursion threshold or to adjust the first duration in response to the load having a value greater than the peak power excursion threshold.
9. The power supply circuit of claim 8 wherein the second circuit includes a calculation circuit for calculating a scaling factor of the off-time duration based at least on a feedback signal from the load.
10. The switched-mode power supply circuit of claim 9 wherein the second circuit is configured to adjust the first duration based at least on the scaling factor.
11. The switched-mode power supply circuit of claim 9 wherein the feedback signal is a voltage and the scaling factor is inversely proportional to the feedback signal.
12. The switched-mode power supply circuit of claim 9 wherein the feedback signal is a current and the scaling factor is directly proportional to the feedback signal.