Secondary Side Post Regulation for LED Backlighting

• US 20070159421A1
• Filed: 01/09/2007
• Published: 07/12/2007
• Est. Priority Date: 01/10/2006
• Status: Active Grant

• Current Assignee: Polaris PowerLED Technologies, LLC (Microchip Technology Incorporated)
• Original Assignee: PowerDsine Limited (Microchip Technology Incorporated)
• Inventors: PEKER, Arkadiy, KORCHARZ, Dror
• Granted Patent: US 7,923,943 B2
• Time in Patent Office: Days
• US Class Current: 345/82
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/06 Handling electromagnetic interferences [EMI], covering emitted as well as received electromagnetic radiation
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/28 using temperature feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

A secondary side post regulator arrangement for a plurality of LED strings. For each secondary winding, a first electronically controlled switch is provided arranged to control the power output, and a LED string is connected thereto. A second electronically controlled switch is further connected in series with the LED string, arranged to receive a PWM signal, thereby pulsing current through the LED string. A current sensing element is further provided outputting a voltage representation of the current through the LED string, and a synchronized sampling circuit is provided arranged to sample the voltage representation during the on period of the second electronically controlled switch. The sampled and held voltage representation is compared with a reference signal and fed back to control the first electronically controlled switch. The voltage output associated with each secondary winding is controlled, responsive to the reference voltage.

Claims

1. A powering arrangement for a plurality of light emitting diode (LED) strings, said powering arrangement comprising:

a transformer exhibiting a primary winding and a plurality of secondary windings coupled to said primary winding;

a first plurality of electronically controlled switches, each of said first plurality of electronically controlled switches associated with a particular one of said plurality of secondary windings;

a plurality of LED strings, each of said plurality of LED strings associated with, and arranged to receive power from, a particular one of said plurality of secondary windings responsive to the respective first electronically controlled switch;

a second plurality of electronically controlled switches, each of said second plurality of electronically controlled switches arranged in series with a particular one of said plurality of LED strings and operable to pulseably enable the flow of current through said particular LED string;

a plurality of synchronized samplers, each of said plurality of synchronized samplers in communication with a particular one of said plurality of LED strings and arranged to sample said pulseably enabled current flow and output a sampled representation; and

a plurality of feedback circuits each associated with a particular one of said plurality of synchronized samplers, each of said plurality of feedback circuits operable to control a respective one of said first electronically controlled switches responsive to said respective sampled representation.

2. A powering arrangement according to claim 1, wherein at least one of said plurality of synchronized samplers comprises a current sensing element arranged to provide a voltage representation of the current through the particular one of the plurality of LED strings.

3. A powering arrangement according to claim 2, wherein said at least one of said plurality of synchronized samplers comprises a synchronized sampling circuit in communication with said current sensing element and operable to sample said voltage representation during said pulseably enabled current flow.

4. A powering arrangement according to claim 3, wherein said synchronized sampling circuit comprises one of a sample and hold circuit and an analog to digital converter.

5. A powering arrangement according to claim 2, wherein said current sensing element comprises one of a resistor and a field effect transistor.

6. A powering arrangement according to claim 1, further comprising a plurality of reference voltages, each of said plurality of feedback circuits being further associated with, and responsive to, a particular one of said plurality of reference voltages, said control of said respective one of said first electronically controlled switches being a function of said respective reference voltage.

7. A powering arrangement according to claim 6, wherein said plurality of reference voltages are variable.

8. A powering arrangement according to claim 6, wherein each of said plurality of feedback circuits comprises a comparing circuit arranged to:

receive said associated reference voltage and said sampled representation; and

output a compared signal responsive to the difference between said received reference voltage and said received sampled representation,

said control of said respective one of said first electronically controlled switch being responsive to said compared signal.

9. A powering arrangement according to claim 6, further comprising a control circuit operable to set the plurality of reference voltages so as to bring each of the plurality of LED strings to a pre-determined luminance.

10. A powering arrangement according to claim 6, further comprising a control circuit operable to set the plurality of reference voltages so as to bring each of the plurality of LED strings to produce a pre-determined white point.

11. A powering arrangement according to claim 10, further comprising a memory associated with said control circuitry, said memory having stored thereon an initial calibration white point setting, said plurality of reference voltages being responsive to said stored initial calibration white point setting.

12. A powering arrangement according to claim 10, wherein said control circuitry further comprises a means for receiving a temperature input, said control circuitry being operable to modify at least one of the plurality of reference voltages responsive to the received temperature input.

13. A powering arrangement according to claim 10, wherein said control circuitry further comprises a means for receiving a color sensor input, said control being operable to modify at least one of the plurality of reference voltages responsive to the received color sensor input so as to maintain said predetermined white point.

14. A powering arrangement according to claim 1, further comprising a plurality of pulse width modulation controllers, each of said second plurality of electronically controlled switches pulseably enabling said current flow responsive to a particular one of said plurality of pulse width modulation controllers.

15. A powering arrangement according to claim 14, further comprising a control circuitry, each of said pulse width modulation controllers being responsive to said control circuitry to modify the luminance of each of plurality of LED strings.

16. A powering arrangement according to claim 14, further comprising a saw tooth voltage source, each of said plurality of pulse width modulation controllers being responsive to said saw tooth voltage source.

17. A powering arrangement according to claim 16, wherein each of said plurality of feedback circuits is further responsive to said saw tooth voltage source.

18. A powering arrangement according to claim 1, further comprising a plurality of one way electronic valves, each of said plurality of one way electronic valves being associated with a particular one of said plurality of secondary windings and in communication with the respective first electronically controlled switch.

19. A powering arrangement according to claim 1, wherein said control of said respective one of said first electronically controlled switches controls the voltage of said power received by the respective LED string.

20. A powering arrangement comprising:

a plurality of DC/DC converters receiving power from a common power source, each of said plurality of DC/DC converters comprising a first electronically controlled switch;

a plurality of second electronically controlled switches, each of said second plurality of electronically controlled switches associated with, and arranged in series with, the output of a particular one of said plurality of DC/DC converters and operable to pulseably enable the flow of current sourced from said particular DC/DC converter through a respective load;

a plurality of synchronized samplers, each of said plurality of synchronized samplers associated with a particular one of said plurality of second electronically controlled switches and arranged to sample said pulseably enabled current flow and output a sampled representation; and

a plurality of feedback circuits each associated with a particular one of said plurality of synchronized samplers, each of said plurality of feedback circuits operable to control a respective one of said first electronically controlled switches responsive to said respective sampled representation.

21. A powering arrangement according to claim 20, wherein said control of said respective one of said first electronically controlled switches thereby controls the output of the respective DC/DC converter.

22. A powering arrangement according to claim 20, further comprising a plurality of reference voltages, each of said plurality of feedback circuits being further associated with, and responsive to, a particular one of said plurality of reference voltages, said control of said respective one of said first electronically controlled switches being a function of said respective reference voltage.

23. A powering arrangement according to claim 22, wherein said plurality of reference voltages are variable.

24. A powering arrangement according to claim 22, wherein each of said plurality of feedback circuits comprises a comparing circuit arranged to:

receive said associated reference voltage and said sampled representation; and

output a compared signal responsive to the difference between said received reference voltage and said received sampled representation,

said control of said respective one of said first electronically controlled switch being responsive to said compared signal.

25. A powering arrangement according to claim 20, wherein each of said plurality of DC/DC converters is arranged to power a light emitting diode (LED) string, the load being constituted of an LED string.

26. A powering arrangement according to claim 20, further comprising a plurality of pulse width modulation controllers, each of said second plurality of electronically controlled switches pulseably enabling said current flow responsive to a particular one of said plurality of pulse width modulation controllers.

27. A powering arrangement for use with a plurality of secondary side regulators enabling intensity control of a light emitting diode backlight by an adjustable pulse width modulation, the powering arrangement comprising:

a plurality of electronically controlled switches, each of said plurality of electronically controlled switches associated with, and arranged for connection in series with, the output of a particular one of a plurality of secondary side regulators and operable to pulseably enable the flow of current through a respective load;

a plurality of synchronized samplers, each of said plurality of synchronized samplers associated with a particular one of said plurality of electronically controlled switches and arranged to sample said pulseably enabled current flow and output a sampled representation; and

a plurality of feedback circuits each associated with a particular one of said plurality of synchronized samplers, each of said plurality of feedback circuits being configured for control of the associated particular secondary side regulator responsive to said respective sampled representation.

28. A powering arrangement according to claim 27, further comprising the plurality of secondary side regulators, said plurality of secondary side regulators receiving power from a common power source.

29. A powering arrangement according to claim 27, further comprising a plurality of reference voltages, each of said plurality of feedback circuits being further associated with, and responsive to, a particular one of said plurality of reference voltages, said control of the associated particular secondary side regulator being a function of said respective reference voltage.

30. A powering arrangement according to claim 29, wherein said plurality of reference voltages are variable.

31. A powering arrangement according to claim 27, wherein each of said plurality of feedback circuits comprises a comparing circuit arranged to:

receive said associated reference voltage and said sampled representation; and

output a compared signal responsive to the difference between said received reference voltage and said received sampled representation,

said control of the associated particular secondary side regulator being responsive to said compared signal.

32. A powering arrangement according to claim 27, further comprising a plurality of pulse width modulation controllers, each of said second plurality of electronically controlled switches pulseably enabling said current flow responsive to a particular one of said plurality of pulse width modulation controllers.

33. A method of powering for a plurality of light emitting diode (LED) strings, said method comprising:

providing a secondary side controller;

providing a LED string associated with said provided secondary side controller;

pulseably enabling current flow through said associated provided LED string;

sampling said pulseably enabled current flow during said pulseably enabled current flow; and

feeding back a function of said sampled pulseably enabled current flow to said provided secondary side controller.

34. A method according to claim 33, further comprising:

receiving a reference voltage, said fed back function back being responsive to said received reference voltage.

35. A method according to claim 34, wherein said reference voltage is variable.

36. A method according to claim 33, wherein said feeding back a function comprises:

receiving a reference voltage;

comparing said received reference voltage and sampled pulseably enabled current flow; and

outputting a comparing signal responsive to the difference between said received reference voltage and said received sampled representation.

37. A powering arrangement for use with a plurality of secondary side regulators enabling intensity control of a light emitting diode backlight by an adjustable pulse width modulation, the powering arrangement comprising:

a plurality of synchronized samplers, each of said plurality of synchronized samplers arranged to sample a pulseably enabled current flow and output a sampled representation; and

a plurality of feedback circuits each associated with a particular one of said plurality of synchronized samplers, each of said plurality of feedback circuits being configured for control of an associated particular secondary side regulator responsive to said sampled representation.