Three-level buck converter configurable for two-level buck converter mode operation
A three-level buck converter circuit configurable to transition between a three-level buck converter mode and a two-level buck converter mode and methods for regulating power using such a circuit. One example power supply circuit generally includes a three-level buck converter circuit and a control circuit coupled to the three-level buck converter circuit and configured to control operation of the three-level buck converter circuit between a three-level buck converter mode and a two-level buck converter mode. The three-level buck converter circuit generally includes a first switch, a second switch coupled to the first switch via a first node, a third switch coupled to the second switch via a second node, a fourth switch coupled to the third switch via a third node, a first capacitive element coupled between the first node and the third node, and an inductive element coupled between the second node and an output node.
1. A power supply circuit comprising:
a three-level buck converter circuit comprising a plurality of switches; and
a control circuit coupled to the three-level buck converter circuit and configured to control operation of the plurality of switches to operate between a three-level buck converter mode and a two-level buck converter mode, wherein the control circuit is configured to control the operation of the plurality of switches to exit the two-level buck converter mode based on an output current of the three-level buck converter circuit being higher than a threshold.
2. The power supply circuit of claim 1 , wherein in the two-level buck converter mode, the control circuit is configured to:
control closure of a first pair of switches in the plurality of switches and control opening of a second pair of switches in the plurality of switches, in a first phase of the two-level buck converter mode; and
control opening of the first pair of switches and control closure of the second pair of switches, in a second phase of the two-level buck converter mode.
3. The power supply circuit of claim 2 , wherein in the two-level buck converter mode, the control circuit is configured to control the closure of the first pair of switches with a constant on-time in the first phase of the two-level buck converter mode.
4. The power supply circuit of claim 2 , wherein in the two-level buck converter mode, the control circuit is configured to control the closure of the first pair of switches according to a peak current in the first phase of the two-level buck converter mode.
5. The power supply circuit of claim 1 , wherein in the two-level buck converter mode, the control circuit is configured to:
control closure of a first group of switches in the plurality of switches and control opening of a second group of switches in the plurality of switches, in a first phase of the two-level buck converter mode; and
control opening of the first group of switches and control opening of the second group of switches, in a second phase of the two-level buck converter mode.
6. The power supply circuit of claim 5 , wherein the three-level buck converter circuit further comprises a first capacitive element and a second capacitive element, coupled to the plurality of switches.
7. The power supply circuit of claim 6 , wherein in the two-level buck converter mode:
the second capacitive element is configured to be effectively connected in series with the first capacitive element in the first phase; and
the second capacitive element is configured to be effectively connected in parallel with the first capacitive element in the second phase.
8. The power supply circuit of claim 6 , wherein a capacitance of the second capacitive element is substantially equal to a capacitance of the first capacitive element.
9. The power supply circuit of claim 5 , wherein an on-time interval of the first phase differs from an off-time interval of the second phase.
10. The power supply circuit of claim 5 , wherein the first group of switches comprises a first trio of switches and wherein the second group of switches comprises a second trio of switches, different from the first trio of switches.
11. The power supply circuit of claim 5 , wherein in the two-level buck converter mode, the control circuit is configured to:
control closure of a switch in the first group of switches based on closure of at least two other switches in the first group of switches; and
control closure of a switch in the second group of switches based on closure of at least two other switches in the second group of switches.
12. The power supply circuit of claim 5 , wherein in the three-level buck converter mode, the control circuit is configured to:
control closure of a first switch in the first group of switches based on closure of a second switch in the first group of switches and a first switch in the second group of switches; and
control closure of a second switch in the second group of switches based on closure of a third switch in the first group of switches and a third switch in the second group of switches.
13. A method of regulating power, the method comprising:
operating a three-level buck converter circuit in a two-level buck converter mode, wherein the three-level buck converter circuit comprises a plurality of switches;
determining an output current of the three-level buck converter circuit, while operating in the two-level buck converter mode, is higher than a threshold; and
based on the determination, exiting the two-level buck converter mode and operating the three-level buck converter circuit in a three-level buck converter mode.
14. The method of claim 13 , wherein operating the three-level buck converter circuit in the two-level buck converter mode comprises:
in a first phase of the two-level buck converter mode, closing a first pair of switches in the plurality of switches and opening a second pair of switches in the plurality of switches; and
in a second phase of the two-level buck converter mode, opening the first pair of switches and closing the second pair of switches.
15. The method of claim 14 , wherein closing the first pair of switches comprises closing the first pair of switches with a constant on-time in the first phase of the two-level buck converter mode.
16. The method of claim 14 , wherein closing the first pair of switches comprises closing the first pair of switches according to a peak current in the first phase of the two-level buck converter mode.
17. The method of claim 13 , wherein operating the three-level buck converter circuit in the two-level buck converter mode comprises:
in a first phase of the two-level buck converter mode, closing a first group of switches in the plurality of switches and opening a second group of switches in the plurality of switches; and
in a second phase of the two-level buck converter mode, opening the first group of switches and closing the second group of switches.
18. The method of claim 17 , wherein the three-level buck converter circuit further comprises a first capacitive element and a second capacitive element, coupled to the plurality of switches, and wherein the method further comprises:
effectively connecting the second capacitive element in series with the first capacitive element in the first phase of the two-level buck converter mode; and
effectively connecting the second capacitive element in parallel with the first capacitive element in the second phase of the two-level buck converter mode.
19. The method of claim 17 , wherein operating the three-level buck converter circuit in the two-level buck converter mode comprises:
closing a switch in the first group of switches based on closure of at least two other switches in the first group of switches; and
closing a switch in the second group of switches based on closure of at least two other switches in the second group of switches.
20. The method of claim 17 , wherein operating the three-level buck converter circuit in the three-level buck converter mode comprises:
closing a first switch in the first group of switches based on closure of a second switch in the first group of switches and a first switch in the second group of switches; and
closing a second switch in the second group of switches based on closure of a third switch in the first group of switches and a third switch in the second group of switches.