Control of four-switch, single inductor, non-inverting buck-boost converters
A power converter includes a buck leg circuit connected between a voltage input of the power converter and ground, a boost leg circuit connected between a voltage output of the power converter and ground, an inductor connected between the buck leg circuit and the boost leg circuit, an error amplifier configured to compare the voltage output of the power converter against a reference voltage to yield a feedback signal, and a control circuit. The control circuit is configured to generate a reference buck ramp configured to be compared against the feedback signal to determine whether to operate the buck leg circuit in buck mode, and to generate a reference boost ramp by superposing a variable boost ramp portion on to the reference buck ramp, the reference boost ramp configured to be compared against the feedback signal to determine whether to operate the boost leg circuit in boost mode.
1. A power converter, comprising:
a buck leg circuit connected between a voltage input of the power converter and ground;
a boost leg circuit connected between a voltage output of the power converter and ground;
an inductor connected between the buck leg circuit and the boost leg circuit;
an error amplifier configured to compare the voltage output of the power converter against a reference voltage to yield a feedback signal; and
a control circuit configured to:
generate a reference buck ramp configured to be compared against the feedback signal to determine whether to operate the buck leg circuit in buck mode; and
generate a reference boost ramp by superposing a variable boost ramp portion on to the reference buck ramp, the reference boost ramp configured to be compared against the feedback signal to determine whether to operate the boost leg circuit in boost mode.
2. The power converter of claim 1 , further comprising a burst mode circuit configured to send a signal to the control circuit to operate the buck leg circuit or the boost leg circuit in a burst mode based upon a determination that a load connected to the power converter has crossed below a threshold value.
3. The power converter of claim 2 , further comprising a clamping circuit configured to modify the feedback signal to at least a minimum value based upon whether the burst mode is to be used.
4. The power converter of claim 3 , wherein the clamping circuit is further configured to modify the feedback signal based upon voltage input and voltage output of the power converter.
5. The power converter of claim 1 , further comprising a current sensor configured to sense current flowing in the power converter, and wherein the control circuit is further configured to generate the reference buck ramp based upon the current sensed by the current sensor.
6. The power converter of claim 5 , wherein the current sensor is configured to sense current in the boost leg circuit.
7. A system, comprising:
a voltage source; and
a power converter configured to receive input from the voltage source at a voltage input of the power converter, the power converter comprising:
a buck leg circuit connected between the voltage input of the power converter and ground;
a boost leg circuit connected between a voltage output of the power converter and ground;
an inductor connected between the buck leg circuit and the boost leg circuit;
an error amplifier configured to compare the voltage output of the power converter against a reference voltage to yield a feedback signal; and
a control circuit configured to:
generate a reference buck ramp configured to be compared against the feedback signal to determine whether to operate the buck leg circuit in buck mode; and
generate a reference boost ramp by superposing a variable boost ramp portion on to the reference buck ramp, the reference boost ramp configured to be compared against the feedback signal to determine whether to operate the boost leg circuit in boost mode.
8. The system of claim 7 , wherein the power converter further comprises a burst mode circuit configured to send a signal to the control circuit to operate the buck leg circuit or the boost leg circuit in a burst mode based upon a determination that a load connected to the power converter has crossed below a threshold value.
9. The system of claim 8 , wherein the power converter further comprises a clamping circuit configured to modify the feedback signal to at least a minimum value based upon whether the burst mode is to be used.
10. The system of claim 9 , wherein the clamping circuit is further configured to modify the feedback signal based upon voltage input and voltage output of the power converter.
11. The system of claim 7 , wherein the power converter further comprises a current sensor configured to sense current flowing in the power converter, and wherein the control circuit is further configured to generate the reference buck ramp based upon the current sensed by the current sensor.
12. The system of claim 11 , wherein the current sensor is configured to sense current in the boost leg circuit.
13. A method of converting power, comprising:
receiving input from a voltage source at a voltage input of a power converter;
with a buck leg circuit connected between the voltage input of the power converter and ground, operating the power converter in buck mode;
with a boost leg circuit connected between a voltage output of the power converter and ground, operating the power converter in boost mode;
connecting an inductor between the buck leg circuit and the boost leg circuit;
with an error amplifier, comparing the voltage output of the power converter against a reference voltage to yield a feedback signal; and
with a control circuit:
generating a reference buck ramp configured to be compared against the feedback signal to determine whether to operate the buck leg circuit in buck mode; and
generating a reference boost ramp by superposing a variable boost ramp portion on to the reference buck ramp, the reference boost ramp configured to be compared against the feedback signal to determine whether to operate the boost leg circuit in boost mode.
14. The method of claim 13 , wherein the power converter further comprises a burst mode circuit configured to send a signal to the control circuit to operate the buck leg circuit or the boost leg circuit in a burst mode based upon a determination that a load connected to the power converter has crossed below a threshold value.
15. The method of claim 14 , wherein the power converter further comprises a clamping circuit configured to modify the feedback signal to at least a minimum value based upon whether the burst mode is to be used.
16. The method of claim 15 , wherein the clamping circuit is further configured to modify the feedback signal based upon voltage input and voltage output of the power converter.
17. The method of claim 13 , wherein the power converter further comprises a current sensor configured to sense current flowing in the power converter, and wherein the control circuit is further configured to generate the reference buck ramp based upon the current sensed by the current sensor.
18. The method of claim 17 , wherein the current sensor is configured to sense current in the boost leg circuit.