Power converter with power switch operable in controlled current mode

1. A power converter, comprising:

a first power switch coupled to a source of electrical power;

a second power switch coupled to said first power switch and to an output terminal of said power converter; and

a controller configured to alternately enable conduction of said first and said second power switches with a duty cycle in response to an output characteristic of said power converter, said controller configured to control a level of current in said first power switch when said second power switch is substantially disabled to conduct.

2. The power converter as recited in claim 1 wherein said controller includes an error amplifier coupled to said output terminal of said power converter to control said level of current in said first power switch.

3. The power converter as recited in claim 1 wherein said controller is configured to provide another mode of operation for said power converter wherein said duty cycle is disabled and said controller controls said level of current in said first power switch in response to said output characteristic.

4. The power converter as recited in claim 1 wherein said second power switch is disabled to conduct in response to a sensed current.

5. The power converter as recited in claim 1 wherein second power switch is disabled to conduct in response to a sensed substantially reversed direction of current through an output inductor of said power converter.

6. The power converter as recited in claim 1 wherein said controller includes a current mirror to control said level of current in said first power switch.

7. The power converter as recited in claim 1 wherein said output characteristic of said power converter is an output voltage of said power converter.

8. The power converter as recited in claim 1 wherein said controller provides two modes of operation for said power converter, comprising:

a first mode of operation wherein said first and second power switches are alternately enabled to conduct in substantially complementary portions of a switching cycle; and

a second mode of operation wherein said first power switch is enabled to conduct for a portion of a switching cycle of said power converter, said second power switch is enabled to conduct for a part of a complementary portion of said switching cycle, wherein conduction of said second power switch is disabled in response to a sensed current of said power converter.

9. The power converter as recited in claim 8 wherein said controller provides a third mode of operation for said power converter including disabling said alternating conduction of said first and second power switches and controlling said level of current in said first power switch.

10. The power converter as recited in claim 9 wherein in said third mode of operation said level of current in said first power switch is controlled in response to said output characteristic.

11. A method of operating a power converter, comprising:

coupling a first power switch to a source of electrical power;

coupling a second power switch to said first power switch and to an output terminal of said power converter;

alternately enabling conduction of said first and said second power switches with a duty cycle in response to an output characteristic of said power converter; and

controlling a level of current in said first power switch when said second power switch is substantially disabled to conduct.

12. The method as recited in claim 11 wherein said controlling is performed in accordance with an error amplifier coupled to said output terminal of said power converter to control said level of current in said first power switch.

13. The method as recited in claim 11 further comprising providing another mode of operation for said power converter wherein said duty cycle is disabled and said controlling controls said level of current in said first power switch in response to said output characteristic.

14. The method as recited in claim 11 wherein said second power switch is disabled to conduct in response to a sensed current.

15. The method as recited in claim 11 wherein second power switch is disabled to conduct in response to a sensed substantially reversed direction of current through an output inductor of said power converter.

16. The method as recited in claim 11 wherein said controlling is performed in accordance with a current mirror to control said level of current in said first power switch.

17. The method as recited in claim 11 wherein said output characteristic of said power converter is an output voltage of said power converter.

18. The method as recited in claim 11 wherein said method provides two modes of operation for said power converter, comprising:

a first mode of operation wherein said first and second power switches are alternately enabled to conduct in substantially complementary portions of a switching cycle; and

a second mode of operation wherein said first power switch is enabled to conduct for a portion of a switching cycle of said power converter, and said second power switch is enabled to conduct for a part of a complementary portion of said switching cycle, wherein conduction of said second power switch is disabled in response to a sensed current of said power converter.

19. The method as recited in claim 18 wherein said method provides a third mode of operation for said power converter including disabling said alternating conduction of said first and second power switches and controlling said level of current in said first power switch.

20. The method as recited in claim 19 wherein in said third mode of operation said level of current in said first power switch is controlled in response to said output characteristic.