Power converter with power switch operable in controlled current mode
A power converter and method of controlling a power switch therein to improve power conversion efficiency at low output current. In one embodiment, the power converter includes a first power switch coupled to a source of electrical power and a second power switch coupled to the first power switch and to an output terminal of the power converter. The power converter also includes a controller configured to alternately enable conduction of the first and the second power switches with a duty cycle in response to an output characteristic of the power converter. The controller is configured to control a level of current in the first power switch when the second power switch is substantially disabled to conduct.
1. A controller for a circuit having first and second switches configured to alternately enable conduction of said first and second switches with a duty cycle in response to an output characteristic of said circuit and control a light level of current in said first switch when said alternately enable conduction of said first and second switches is disabled.
2. The controller as recited in claim 1 wherein said controller is configured to control said light level of current in said first power switch when said second power switch is enabled to conduct.
3. The controller as recited in claim 1 wherein said controller is configured to control said light level of current in said first power switch in response to an increase of a sensed current of said circuit.
4. The controller as recited in claim 1 comprising an error amplifier configured to control said light level of current in said first power switch.
5. The controller as recited in claim 1 comprising a current mirror configured to control said light level of current in said first power switch.
6. The controller as recited in claim 1 wherein said controller is configured to enable conduction of said first switch for a portion of a switching cycle of said circuit, enable conduction of said second switch for a part of a complementary portion of said switching cycle, and disable conduction of said second switch in response to a sensed current of said circuit.
7. The controller as recited in claim 1 wherein said controller is configured to control said light level of current in said first switch in response to said output characteristic.
8. A method, comprising:
alternately enabling conduction of first and second switches with a duty cycle in response to an output characteristic of a circuit; and
controlling a light level of current in said first switch when said alternately enable conduction of said first and second switches is disabled.
9. The method as recited in claim 8 wherein said controlling said light level of current in said first power switch is performed when said second power switch is enabled to conduct.
10. The method as recited in claim 8 wherein said controlling said light level of current in said first power switch comprises controlling said light level of current in said first power switch in response to an increase of a sensed current of said circuit.
11. The method as recited in claim 8 wherein said controlling is performed in accordance with a current mirror.
12. The method as recited in claim 8 wherein said controlling is performed in accordance with an error amplifier.
13. The method as recited in claim 8 , further comprising:
enabling conduction of said first switch for a portion of a switching cycle of said circuit;
enabling conduction of said second switch for a part of a complementary portion of said switching cycle; and
disabling conduction of said second switch in response to a sensed current of said circuit.
14. The method as recited in claim 8 wherein said controlling said light level of current in said first power switch is in response to said output characteristic.
15. A circuit, comprising:
first and second switches; and
a controller configured to alternately enable conduction of said first and second switches with a duty cycle in response to an output characteristic of said circuit and control a light level of current in said first switch when said alternately enable conduction of said first and second switches is disabled.
16. The circuit as recited in claim 15 wherein said controller is configured to control said light level of current in said first power switch when said second power switch is enabled to conduct.
17. The circuit as recited in claim 15 wherein said controller is configured to control said light level of current in said first power switch in response to an increase of a sensed current of said circuit.
18. The circuit as recited in claim 15 wherein said controller comprises one of an error amplifier and a current mirror configured to control said light level of current in said first power switch.
19. The circuit as recited in claim 15 wherein said controller is configured to enable conduction of said first switch for a portion of a switching cycle of said circuit, enable conduction of said second switch for a part of a complementary portion of said switching cycle, and disable conduction of said second switch in response to a sensed current of said circuit.
20. The circuit as recited in claim 15 wherein said controller is configured to control said light level of current in said first switch in response to said output characteristic.