Multi-level power converter with light load flying capacitor voltage regulation
A multi-level power converter and a method using first, second, third and fourth switching elements, an inductor, and a flying capacitor are presented. A first terminal of the inductor may be connected to a switching terminal connecting the second and third switching elements. A first terminal of the flying capacitor may be connected to a terminal connecting the first and second elements. A second terminal of the flying capacitor may be connected to a terminal connecting the third and fourth switching elements. The multi-level power converter may have a first feedback circuit to generate control signals for setting the switching elements in a plurality of switching states for regulating an output voltage or an output current. The converter may have a second feedback circuit to generate control signals to allow the flying capacitor to be charged or discharged using an inductor current flowing through the inductor.
1. A multi-level power converter comprising:
a first switching element, a second switching element, a third switching element, and a fourth switching element;
an inductor, wherein a first terminal of said inductor is connected to a switching terminal connecting the second switching element and the third switching element;
a flying capacitor, wherein a first terminal of said flying capacitor is connected to a terminal connecting the first switching element and the second switching element, and wherein a second terminal of said flying capacitor is connected to a terminal connecting the third switching element and the fourth switching element;
a first feedback circuit configured to generate control signals for setting the switching elements in a plurality of switching states for regulating an output voltage or an output current of the multi-level power converter; and
a second feedback circuit configured to generate, based on a capacitor voltage across the flying capacitor, temporary control signals for setting the switching elements in a temporary switching state in which the flying capacitor is charged or discharged using an inductor current flowing through the inductor;
wherein the second feedback circuit comprises a delay circuit configured
to receive at least one of the control signals generated by the first feedback circuit, and
to generate at least one of the temporary control signals by delaying said at least one control signal by a delay interval.
2. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to generate said temporary control signals for controlling the switching elements in the temporary switching state during a time interval between a preceding switching state and a subsequent switching state, wherein both the preceding and the subsequent switching states are selected by the first feedback circuit from said plurality of switching states.
3. The multi-level power converter of claim 1 , wherein the temporary switching state of the second feedback circuit is not one of the plurality of switching states of the first feedback circuit.
4. The multi-level power converter of claim 1 , wherein the plurality of switching states includes a first switching state and a second switching state, wherein in the first switching state the first and the second switching elements are turned off and the third and the fourth switching elements are turned on, and wherein in the second switching state the first and the second switching elements are turned on and the third and the fourth switching elements are turned off.
5. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to determine the delay interval such that a frequency of voltage change of the capacitor voltage is outside of an audible frequency band.
6. The multi-level power converter of claim 1 , wherein
the first feedback circuit is configured to generate two control signals for turning off the first and the second switching element almost simultaneously, and
the second feedback circuit is configured to select one of the two control signals based on the capacitor voltage, and to delay the selected one of the two control signals by the delay interval such that the flying capacitor is charged or discharged by the inductor current during said delay interval.
7. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to
if the capacitor voltage is below a target voltage value, generate a first temporary control signal for turning off the first switching element by delaying a first control signal generated by the first feedback circuit for turning off the first switching element, or
if the capacitor voltage is larger than the target voltage value, generate a second temporary control signal for turning off the second switching element by delaying a second control signal generated by the first feedback circuit for turning off the second switching element.
8. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to
if the capacitor voltage is below a target voltage value, generate the second temporary control signal for turning off the second switching element by forwarding a second control signal generated by the first feedback circuit for turning off the second switching element, or
if the capacitor voltage is larger than the target voltage value, generate the first temporary control signal for turning off the first switching element by forwarding a first control signal generated by the first feedback circuit for turning off the first switching element.
9. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to
if the capacitor voltage is larger than a target voltage value, generate a third temporary control signal for turning off the third switching element by delaying a third control signal generated by the first feedback circuit for turning off the third switching element, or
if the capacitor voltage is below the target voltage value, generate a fourth temporary control signal for turning off the fourth switching element by delaying a fourth control signal generated by the first feedback circuit for turning off the fourth switching element.
10. The multi-level power converter of claim 1 , wherein the second feedback circuit is configured to
if the capacitor voltage is larger than a target voltage value, generate the fourth temporary control signal for turning off the fourth switching element by forwarding a fourth control signal generated by the first feedback circuit for turning off the fourth switching element, or
if the capacitor voltage is below the target voltage value, generate the third temporary control signal for turning off the third switching element by forwarding the third control signal generated by the first feedback circuit for turning off the third switching element.
11. The multi-level power converter of claim 1 , wherein the second feedback circuit further comprises:
a comparator configured to compare the capacitor voltage against a target capacitor voltage; and
at least one multiplexer, wherein each multiplexer is wherein each multiplexer is configured to forward, based on a comparison result generated by the comparator, either one of the control signals generated by the first feedback circuit or one of the temporary control signals generated by the second feedback circuit for controlling a switching behavior of one of the switching elements.
12. The multi-level power converter of claim 11 , wherein a hysteresis of the comparator is selected such that a frequency of voltage change of the capacitor voltage is outside of an audible frequency band.
13. A method of operating a multi-level power converter comprising a first switching element, a second switching element, a third switching element, a fourth switching element, an inductor, and a flying capacitor, wherein a first terminal of said inductor is connected to a switching terminal connecting the second switching element and the third switching element, wherein a first terminal of said flying capacitor is connected to a terminal connecting the first switching element and the second switching element, and wherein a second terminal of said flying capacitor is connected to a terminal connecting the third switching element and the fourth switching element, the method comprising the steps of:
generating, by a first feedback circuit, control signals for setting the switching elements in a plurality of switching states for regulating an output voltage or an output current of the multi-level power converter;
generating, by a second feedback circuit, based on a capacitor voltage across the flying capacitor, temporary control signals for setting the switching elements in a temporary switching state in which the flying capacitor is charged or discharged using an inductor current flowing through the inductor;
receiving, by the second feedback circuit, at least one of the control signals generated by the first feedback circuit, and
generating, by the second feedback circuit, at least one of the temporary control signals by delaying said at least one control signal by a delay interval.
14. The method of claim 13 , further comprising the step of:
generating, by the second feedback circuit, said temporary control signals for controlling the switching elements in the temporary switching state during a time interval between a preceding switching state and a subsequent switching state, wherein both the preceding and the subsequent switching states are selected by the first feedback circuit from said plurality of switching states.
15. The method according to claim 13 , wherein the temporary switching state of the second feedback circuit is not one of the plurality of switching states of the first feedback circuit.
16. The method according to claim 13 , wherein the plurality of switching states includes a first switching state and a second switching state, wherein in the first switching state the first and the second switching elements are turned off and the third and the fourth switching elements are turned on, and wherein in the second switching state the first and the second switching elements are turned on and the third and the fourth switching elements are turned off.
17. The method according to claim 13 , further comprising the step of:
determining, by the second feedback circuit, the delay interval such that a frequency of voltage change of the capacitor voltage is outside of an audible frequency band.
18. The method according to claim 13 , further comprising the steps of:
generating, by the first feedback circuit, two control signals for turning off the first and the second switching element almost simultaneously,
selecting, by the second feedback circuit, one of the two control signals based on the capacitor voltage, and
delaying, by the second feedback circuit, the selected one of the two control signals by the delay interval such that the flying capacitor is charged or discharged by the inductor current during said delay interval.
19. The method according to claim 13 , further comprising the steps of:
if the capacitor voltage is below a target voltage value, generating a first temporary control signal for turning off the first switching element by delaying a first control signal generated by the first feedback circuit for turning off the first switching element, or
if the capacitor voltage is larger than the target voltage value, generating a second temporary control signal for turning off the second switching element by delaying a second control signal generated by the first feedback circuit for turning off the second switching element.
20. The method according to claim 19 , further comprising the steps of:
if the capacitor voltage is below the target voltage value, generating the second temporary control signal for turning off the second switching element by forwarding a second control signal generated by the first feedback circuit for turning off the second switching element, or
if the capacitor voltage is larger than the target voltage value, generating the first temporary control signal for turning off the first switching element by forwarding a first control signal generated by the first feedback circuit for turning off the first switching element.
21. The method according to claim 13 , further comprising the steps of:
if the capacitor voltage is larger than a target voltage value, generating a third temporary control signal for turning off the third switching element by delaying a third control signal generated by the first feedback circuit for turning off the third switching element, or
if the capacitor voltage is below the target voltage value, generating a fourth temporary control signal for turning off the fourth switching element by delaying a fourth control signal generated by the first feedback circuit for turning off the fourth switching element for turning off the fourth switching element.
22. The method according to claim 21 , further comprising the steps of:
if the capacitor voltage is larger than the target voltage value, generating the fourth temporary control signal for turning off the fourth switching element by forwarding a fourth control signal generated by the first feedback circuit for turning off the fourth switching element, or
if the capacitor voltage is below the target voltage value, generating the third temporary control signal for turning off the third switching element by forwarding the third control signal generated by the first feedback circuit for turning off the third switching element.
23. The method according to claim 13 , wherein the second feedback circuit comprises a delay circuit, a comparator, and at least one multiplexer, the method further comprising the steps of:
generating, by the delay circuit the temporary control signals by delaying the control signals generated by the first feedback circuit;
comparing, by the comparator, the capacitor voltage against a target capacitor voltage; and
forwarding, by each multiplexer, based on a comparison result generated by the comparator, either one of the control signals generated by the first feedback circuit or one of the temporary control signals generated by the second feedback circuit for controlling a switching behavior of one of the switching elements.
24. The method according to claim 23 , further comprising the step of:
selecting a hysteresis of the comparator such that a frequency of voltage change of the capacitor voltage is outside of an audible frequency band.