Methods for extending holdup times and/or reducing bulk capacitors in multi-stage switching power supplies
View Patent ↗A multi-stage switching power supply includes a first DC-DC power converter, a second DC-DC power converter and a control circuit. The control circuit is coupled to the DC-DC power converters for providing a first control signal to the first DC-DC power converter and a second control signal to the second DC-DC power converter. The control circuit is configured to vary a duty cycle of the first control signal to regulate an output voltage of the power supply, maintain a frequency of the second control signal at a fixed frequency, and in response to the duty cycle of the first control signal reaching a duty cycle threshold or an input voltage of the first DC-DC power converter reaching a voltage threshold, vary a frequency of the second control signal to regulate the output voltage of the power supply. Other example power supplies, control circuits, etc. are also disclosed.
1. A multi-stage switching power supply comprising:
an input;
an output for providing an output voltage to a load;
at least two power converters coupled between the input and the output, the at least two power converters including a first DC-DC power converter having at least one power switch and a second DC-DC power converter having at least one power switch, wherein the second DC-DC power converter is a resonant power converter; and
a control circuit coupled to the at least two DC-DC power converters for providing a first control signal to the power switch of the first DC-DC power converter and a second control signal to the power switch of the second DC-DC power converter, the control circuit configured to vary a duty cycle of the first control signal to regulate the output voltage of the power supply, maintain a frequency of the second control signal at a fixed frequency, and in response to the duty cycle of the first control signal reaching a defined duty cycle threshold or an input voltage of the first DC-DC power converter reaching a defined voltage threshold, vary the frequency of the second control signal to regulate the output voltage of the power supply.
2. The multi-stage switching power supply of claim 1 wherein the first DC-DC power converter is coupled between the input and the second DC-DC power converter.
3. The multi-stage switching power supply of claim 1 further an AC-DC power converter coupled between the input and the first DC-DC power converter.
4. The multi-stage switching power supply of claim 1 wherein the control circuit is configured to vary the duty cycle of the first control signal between the defined duty cycle threshold and a duty cycle lower than the defined duty cycle threshold.
5. The multi-stage switching power supply of claim 1 wherein the control circuit is configured to vary the frequency of the second control signal from a first defined frequency to a second defined frequency lower than the first defined frequency.
6. The multi-stage switching power supply of claim 1 wherein the control circuit is configured to vary the frequency of the second control signal in response to the duty cycle of the first control signal reaching the defined duty cycle threshold.
7. The multi-stage switching power supply of claim 1 wherein the control circuit is configured to maintain the duty cycle at the defined duty cycle threshold when the frequency of the second control signal is varied.
8. The multi-stage switching power supply of claim 1 wherein the control circuit is configured to vary the frequency of the second control signal in response to the input voltage of the first DC-DC power converter reaching the defined voltage threshold.
9. A method for regulating an output voltage of a multi-stage switching power supply, the multi-stage switching power supply including at least two power converters having a first DC-DC power converter and a second DC-DC power converter, wherein the second DC-DC power converter is a resonant power converter, the method comprising:
varying a duty cycle of a first control signal provided to at least one power switch of the first DC-DC power converter and maintaining a fixed frequency of a second control signal provided to at least one power switch of the second DC-DC power converter to regulate the output voltage of the multi-stage switching power supply; and
in response to the duty cycle of the first control signal reaching a defined duty cycle threshold or an input voltage of the first DC-DC power converter reaching a defined voltage threshold, varying a frequency of a second control signal provided to at least one power switch of the second DC-DC power converter to regulate the output voltage of the multi-stage switching power supply.
10. The method of claim 9 wherein varying the duty cycle of the first control signal includes varying the duty cycle of the first control signal between the defined duty cycle threshold and a duty cycle lower than the defined duty cycle threshold.
11. The method of claim 9 wherein varying the frequency of the second control signal includes varying the frequency of the second control signal from a first defined frequency to a second defined frequency lower than the first defined frequency.
12. The method of claim 9 wherein varying the frequency of the second control signal includes varying the frequency of the second control signal in response to the duty cycle of the first control signal reaching the defined duty cycle threshold.
13. The method of claim 9 wherein varying the frequency of the second control signal includes varying the frequency of the second control signal in response to the input voltage of the first DC-DC power converter reaching the defined voltage threshold.
14. The method of claim 9 wherein maintaining a fixed frequency of the second control signal includes maintaining a fixed frequency of the second control signal when the duty cycle of the first control signal is less than the defined duty cycle threshold or the voltage received by the first DC-DC power converter is less than the defined voltage threshold.
15. A control circuit for regulating an output voltage of a multi-stage switching power supply, the multi-stage switching power supply including an input, an output for providing an output voltage to a load, and at least two power converters coupled between the input and the output, the at least two power converters including a first DC-DC power converter having at least one power switch and a second DC-DC power converter having at least one power switch, wherein the second DC-DC power converter is a resonant power converter, and wherein the control circuit is configured to couple to the at least two DC-DC power converters for providing a first control signal to the power switch of the first DC-DC power converter and a second control signal to the power switch of the second DC-DC power converter, vary a duty cycle of the first control signal to regulate the output voltage of the power supply, maintain a frequency of the second control signal at a fixed frequency, and in response to the duty cycle of the first control signal reaching a defined duty cycle threshold or a voltage received by the first DC-DC power converter reaching a defined voltage threshold, vary the frequency of the second control signal to regulate the output voltage.
16. The control circuit of claim 15 wherein the control circuit is configured to vary the duty cycle of the first control signal between the defined duty cycle threshold and a duty cycle lower than the defined duty cycle threshold.
17. The control circuit of claim 15 wherein the control circuit is configured to vary the frequency of the second control signal from a first defined frequency to a second defined frequency lower than the first defined frequency.
18. The control circuit of claim 15 wherein the control circuit is configured to maintain the duty cycle at the defined duty cycle threshold when the frequency of the second control signal is varied.
19. The control circuit of claim 15 wherein the control circuit is configured to vary the frequency of the second control signal in response to the duty cycle of the first control signal reaching the defined duty cycle threshold.
20. The control circuit of claim 15 wherein the control circuit is configured to vary the frequency of the second control signal in response to the voltage received by the first DC-DC power converter reaching the defined voltage threshold.
21. The multi-stage switching power supply of claim 1 wherein the first DC-DC power converter includes a buck power converter.
22. The multi-stage switching power supply of claim 21 wherein the second DC-DC power converter includes an LLC resonant power converter.
23. The multi-stage switching power supply of claim 3 wherein the AC-DC power converter includes a boost PFC power converter.