Power supply with reduced power consumption when a load is disconnected from the power supply

• US 20090116269A1
• Filed: 11/02/2007
• Published: 05/07/2009
• Est. Priority Date: 11/02/2007
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Hopper, Peter J., Yegnashankaran, Visvamohan
• Granted Patent: US 7,764,517 B2
• Time in Patent Office: Days
• US Class Current: 363/84
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• 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: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

Detection and control circuitry are added to a conventional power supply to detect when a load, such as a portable electronic device, has been disconnected from the power supply and, when disconnected, interrupt a current path to the primary windings of a transformer within the power supply to substantially reduce the amount of reactive power that is consumed by the power supply.

Claims

1. A power supply comprising:

a transformer having a primary winding and a secondary winding;

a rectifier connected to the secondary winding of the transformer;

a filter connected to the rectifier, the filter having an output;

a conductive line connected to the output of the filter; and

a current sensor that detects a current flowing out of the filter and down the conductive line, the current having a current magnitude.

2. The power supply of claim 1 and further comprising a switch connected to the primary winding of the transformer.

3. The power supply of claim 2 and further comprising a controller connected to the current sensor and the switch, the controller outputting an open signal and a closed signal to the switch.

4. The power supply of claim 3 wherein:

when the current sensor detects that the current magnitude is less than a minimum magnitude, the controller outputs the open signal to the switch; and

the switch opens and remains open in response to the open signal.

5. The power supply of claim 4 wherein after the controller has output the open signal, the controller outputs the closed signal a predetermined time later.

6. The power supply of claim 5 wherein after the controller has output the closed signal, the controller outputs the open signal to the switch a predefined time later when the current sensor detects that the current magnitude remains less than the minimum magnitude.

7. The power supply of claim 6 and further comprising:

an AC input connected to the switch, the AC input receiving a low-frequency AC; and

a controller power supply connected to the AC input and the controller, the controller receiving an operating voltage and current from the controller power supply.

8. The power supply of claim 7 wherein the controller continuously receives the operating voltage and current from the controller power supply as long as the AC input receives the low-frequency AC.

9. The power supply of claim 2 wherein the switch opens and closes at a switching frequency to generate a high-frequency AC.

10. The power supply of claim 9 and further comprising a controller connected to the current sensor and the switch, the controller controlling the switching frequency of the switch.

11. The power supply of claim 10 wherein:

when the current sensor detects that the current magnitude is less than a minimum magnitude, the controller outputs a halt and open signal to the switch; and

the switch stops switching, opens, and remains open in response to the halt and open signal.

12. The power supply of claim 11 wherein after the controller has output the halt and open signal, the controller outputs a resume signal a predetermined time later, the switch switching at the switching frequency in response to the resume signal.

13. The power supply of claim 12 wherein after the controller has output the resume signal, the controller outputs the halt and open signal to the switch a predefined time later when the current sensor detects that the current magnitude remains less than the minimum magnitude.

14. The power supply of claim 13 and further comprising:

an AC input receiving a low-frequency AC;

an input rectifier connected to the AC input;

a filter connected to the input rectifier and the switch; and

a controller power supply connected to the AC input and the controller, the controller receiving an operating voltage and current from the controller power supply.

15. The power supply of claim 14 wherein the controller continuously receives the operating voltage and current from the controller power supply as long as the AC input receives the low-frequency AC.

16. A method of controlling a power supply, the method comprising:

detecting when a magnitude of a current flowing down a conductive line is less than a minimum magnitude; and

opening and leaving open a switch when the magnitude of the current is less than the minimum magnitude, the switch being connected to a primary winding of a transformer.

17. The method of claim 16 and further comprising closing the switch a predetermined time after the switch was opened.

18. The method of claim 17 and further comprising after the switch has been closed, opening and leaving open the switch a predefined time later when the magnitude of the current remains less than the minimum magnitude.

19. The method of claim 16 and further comprising resuming a switching of the switch a predetermined time after the switch was opened.

20. The method of claim 19 and further comprising after the switch has resumed switching, opening and leaving open the switch a predefined time later when the magnitude of the current remains less than the minimum magnitude.