Start-up circuit for a power adapter

• US 9,077,248 B2
• Filed: 07/03/2012
• Issued: 07/07/2015
• Est. Priority Date: 06/17/2009
• Status: Active Grant

• Current Assignee: Power Systems Technologies Company Limited (Flex, Ltd.)
• Original Assignee: Power Systems Technologies Company Limited (Flex, Ltd.)
• Inventors: Brinlee, Antony
• Primary Examiner(s): DEBERADINIS, ROBERT L
• Application Number:
  US13/541,523
• Publication Number:
  US 20120294048A1
• Time in Patent Office: 1,099 Days
• Field of Search: 307/140
• US Class Current: 1/1
• CPC Class Codes: H02M 1/126 using passive filters
• CPC Class Codes: H02M 1/322 Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 7/05 Capacitor coupled rectifiers

Abstract

A start-up circuit for a power adapter and method of operating the same. In one embodiment, the power adapter includes a start-up circuit configured to provide an initial bias voltage for the power adapter. The power adapter also includes a crowbar circuit configured to turn on the start-up circuit upon loss of an ac mains voltage supplied to the power adapter.

Claims

1. A power adapter, comprising:

a start-up circuit configured to provide an initial bias voltage for said power adapter; and

a crowbar circuit configured to turn on said start-up circuit upon loss of an ac mains voltage supplied to said power adapter.

2. The power adapter as recited in claim 1 wherein said start-up circuit comprises a switch and resistor coupled thereto configured to provide a substantially constant-current bias voltage source.

3. The power adapter as recited in claim 2 wherein said switch is a metal-oxide semiconductor field-effect transistor and said resistor is series-coupled to a source terminal thereof.

4. The power adapter as recited in claim 1 wherein said start-up circuit employs said ac mains voltage to provide said initial bias voltage.

5. The power adapter as recited in claim 1 wherein said start-up circuit is coupled to said ac mains voltage via a diode bridge.

6. The power adapter as recited in claim 1 wherein said crowbar circuit is configured to turn on said start-up circuit when said ac mains voltage falls below a threshold level.

7. The power adapter as recited in claim 1 wherein said start-up circuit comprises a double-diffused metal-oxide semiconductor start-up cell.

8. The power adapter as recited in claim 1 wherein said crowbar circuit comprises a resistor-capacitor network coupled to said ac mains voltage.

9. The power adapter as recited in claim 1 wherein said crowbar circuit comprises a diode bridge coupled via a resistor-capacitor network to said ac mains voltage.

10. The power adapter as recited in claim 1 wherein said crowbar circuit is isolated from a bias voltage filter capacitor by a diode.

11. The power adapter as recited in claim 1 wherein said crowbar circuit comprises a switch coupled to a capacitor through a diode.

12. The power adapter as recited in claim 11 wherein said switch as a bipolar transistor.

13. The power adapter as recited in claim 1 wherein said start-up circuit is operable to discharge a capacitor coupled across input terminals of said power adapter.

14. The power adapter as recited in claim 12 wherein said capacitor is an X-capacitor.

15. The power adapter as recited in claim 1 wherein said start-up circuit is configured to provide said initial bias voltage when a bias voltage of said power adapter is less than a threshold value.

16. A method, comprising:

providing an initial bias voltage for a power adapter with a start-up circuit; and

turning on said start-up circuit upon loss of an ac mains voltage supplied to said power adapter.

17. The method as recited in claim 16 wherein said start-up circuit provides a substantially constant-current bias voltage source.

18. The method as recited in claim 16 wherein said turning on said start-up circuit comprises turning on said start-up circuit when said ac mains voltage falls below a threshold level.

19. The method as recited in claim 16 furthering comprising discharging a capacitor coupled across input terminals of said power adapter.

20. The method as recited in claim 16 wherein providing said initial bias voltage comprises providing said initial bias voltage when a bias voltage of said power adapter is less than a threshold value.