Control method for zero voltage switching buck-boost power converters
A method comprises providing a buck-boost converter comprising a first high-side switch and a first low-side switch connected in series across an input capacitor, a second high-side switch and a second low-side switch connected in series across an output capacitor and an inductor coupled between a common node of the first high-side switch and the first low-side switch, and a common node of the second high-side switch and the second low-side switch, detecting a first voltage resonance waveform across a switch of the buck-boost converter and turning on the switch of the buck-boost converter when the first voltage resonance waveform falls to zero.
1. A method comprising:
detecting one or more voltage resonance waveforms across a switch of a buck-boost converter, wherein the buck-boost converter comprises a first high-side switch and a first low-side switch connected in series across an input capacitor, a second high-side switch and a second low-side switch connected in series across an output capacitor and an inductor coupled between a common node of the first high-side switch and the first low-side switch, and a common node of the second high-side switch and the second low-side switch; and
turning on the switch of the buck-boost converter after the one or more voltage resonance waveforms fall to a voltage approximately equal to zero, wherein, prior to turning on the switch, a voltage across the switch falls to a first voltage approximately equal to zero and increases from the first voltage to a second voltage greater than zero.
2. The method of claim 1 , wherein:
the inductor resonates with a drain-to-source capacitor to generate the one or more voltage resonance waveforms.
3. The method of claim 1 , wherein:
turning on the switch of the buck-boost converter after the one or more voltage resonance waveforms fall to a voltage approximately equal to zero includes turning on the switch of the buck-boost converter after a first voltage resonance waveform falls to zero.
4. The method of claim 1 , wherein:
turning on the switch of the buck-boost converter after the one or more voltage resonance waveforms fall to a voltage approximately equal to zero includes turning on the switch of the buck-boost converter when a last voltage resonance waveform of the one or more voltage resonance waveforms falls to zero.
5. The method of claim 4 , further comprising:
configuring the buck-boost converter to operate at a fixed switching frequency by selecting a number of the voltage resonance waveforms between a first voltage resonance waveform and a turn-on time of the switch of the buck-boost converter.
6. The method of claim 4 , further comprising:
under a light load operating condition, limiting a maximum switching frequency of the buck-boost converter by selecting a number of the voltage resonance waveforms between a first voltage resonance waveform and a turn-on time of the switch of the buck-boost converter.
7. The method of claim 1 , wherein:
during a buck operating mode, the switch is the first high-side switch.
8. The method of claim 1 , wherein:
during a boost operating mode, the switch is the second low-side switch.
9. The method of claim 1 , further comprising:
configuring the buck-boost converter to operate in a buck operating mode, wherein the switch is the first high-side switch.
10. The method of claim 1 , further comprising:
configuring the buck-boost converter to operate in a boost operating mode, wherein the switch is the second low-side switch.
11. An apparatus comprising:
a buck converter portion comprising a first high-side switch and a first low-side switch connected in series across an input capacitor;
a boost converter portion comprising a second high-side switch and a second low-side switch connected in series across an output capacitor;
an inductor coupled between the buck converter portion and the boost converter portion, wherein the buck converter portion, the boost converter portion and the inductor form a buck-boost converter; and
a controller configured to:
detect a first voltage resonance waveform across a switch of the buck-boost converter, wherein the first voltage resonance waveform includes a peak and two valleys; and
turn on the switch of the buck-boost converter after the first voltage resonance waveform falls to zero.
12. The apparatus of claim 11 , wherein the controller is configured to:
operate the buck-boost converter in a buck operating mode and turn on the first high-side switch of the buck-boost converter when a first voltage resonance waveform across the first high-side switch falls to a voltage approximately equal to zero.
13. The apparatus of claim 11 , wherein the controller is configured to:
operate the buck-boost converter in a boost operating mode and turn on the second low-side switch of the buck-boost converter when a first voltage resonance waveform across the second low-side switch falls to a voltage approximately equal to zero.
14. The apparatus of claim 11 , wherein the controller is configured to:
operate the buck-boost converter in a buck operating mode and turn on the first high-side switch of the buck-boost converter when a last resonance waveform of a plurality of voltage resonance waveforms across the first high-side switch falls to a voltage approximately equal to zero.
15. The apparatus of claim 11 , wherein the controller is configured to:
operate the buck-boost converter in a boost operating mode and turn on the second low-side switch of the buck-boost converter when a last resonance waveform of a plurality of voltage resonance waveforms across the second low-side switch falls to a voltage approximately equal to zero.
16. The apparatus of claim 11 , wherein the controller is configured to:
detect the first voltage resonance waveform across the switch of the buck-boost converter, and wherein the first voltage resonance waveform is generated by a resonance process between the inductor and a drain-to-source capacitor of the switch.
17. The apparatus of claim 11 , wherein the controller is configured to:
operate the buck-boost converter in a fixed switching frequency mode by selecting a number of voltage resonance waveforms between the first voltage resonance waveform and a turn-on time of the switch of the buck-boost converter.
18. The apparatus of claim 17 , wherein:
at least one voltage resonance waveform is between the first voltage resonance waveform and the turn-on time of the switch of the buck-boost converter.
19. The apparatus of claim 11 , wherein the controller is configured to:
under a light load operating condition, limit a maximum switching frequency of the buck-boost converter by selecting a number of voltage resonance waveforms between the first voltage resonance waveform and a turn-on time of the switch of the buck-boost converter.
20. The apparatus of claim 19 , wherein:
at least one voltage resonance waveform is between the first voltage resonance waveform and the turn-on time of the switch of the buck-boost converter.