Method and circuit design for a self-calibrating control device

Abstract

Circuit design for controlling one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED driver devices (44; 54; 60, 61, 62; 700, 701, 702), wherein the circuit design comprises: a programmable control device (42; 52; 66; 706, 709) coupled to one or more detectors (41; 51; 63, 64, 65; 703, 704, 705), wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) are configured to detect one or more measurable parameters of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED driver devices (44; 54; 60, 61, 62; 700, 701, 702), wherein the control device (42; 52; 66; 706, 709) is configured to receive information from the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) relating to the one or more measurable parameters, characterized by the fact that the control unit (42; 52; 66; 706, 709) is decentralized, the control device (42; 52; 66; 706, 709) is configured to set one or more controllable parameters until one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) indicate that one or more parameters in one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED driver devices (44; 54; 60, 61, 62; 700, 701, 702) satisfy a reference condition, and wherein the control device is configured to set one or more of the controllable parameters for operation at a value that is a function of the value of the controllable parameter at which the reference condition is met.

Description

[0001] This application is a continuation-in-part of U.S. Patent Application No. 12 / 046,280 filed March 11, 2008 and U.S. Patent Application No. 12 / 111,114 filed April 28, 2008, which are incorporated herein by reference in their entirety. Field of invention

[0002] The present invention relates to LED strings for backlighting electronic displays and / or other electronic systems. More particularly, the present invention relates to circuits and methods for efficiently controlling LEDs and LED drivers based on parameters such as voltage, current, power, temperature, light intensity, and wavelength. Background of the invention

[0003] Backlights are used to illuminate liquid crystal displays ("LCDs"). LCDs with backlights are used in small displays for mobile phones and PDAs, as well as in large displays for computer monitors and televisions. The backlight light source often includes one or more cold cathode fluorescent lamps ("CCFLs"). The backlight light source can also include an incandescent lamp, an electroluminescent panel ("ELP"), or one or more hot cathode fluorescent lamps ("HCFLs").

[0004] Display manufacturers are increasingly pursuing the use of LEDs as a backlight light source because CCFLs have many disadvantages: they are not easily activated in cold temperatures, require a certain idle time before activation, and must be handled carefully. Furthermore, LEDs generally have a higher light-to-power ratio than other backlight light sources. Therefore, displays with LED backlights consume less power than other displays. LED backlights have traditionally been used primarily in small, inexpensive LCD panels. However, LED backlights are gradually gaining acceptance in large displays such as those used in computers and televisions. In large displays, multiple LEDs are required to provide adequate backlighting for the LCD.

[0005] Circuit designs for controlling multiple LEDs in large displays are usually designed in such a way that the LEDs are distributed across several chains. Fig. 1 shows an exemplary flat panel display 10 with a backlight system having three independent LED strings 1, 2, and 3. The first LED string 1 comprises seven LEDs 4, 5, 6, 7, 8, 9, and 11 distributed across the display 10 and connected in series. The first string 1 is controlled by the drive circuit 12. The second string 2 is controlled by the drive circuit 13, and the third string 3 is controlled by the drive circuit 14. The LEDs of the LED strings 1, 2, and 3 can be connected in series by wires, conductors, or other connecting elements.

[0006] Fig. 2 shows another exemplary flat panel display 20 with a backlight system comprising three independent LED strings 21, 22, and 23. In this embodiment, the strings 21, 22, and 23 are arranged vertically. The three strings 21, 22, and 23 are arranged parallel to each other. The first string 21 comprises seven LEDs 24, 25, 26, 27, 28, 29, and 31 connected in series and is controlled by drive circuit 32. The second string 22 is controlled by drive circuit 33, and the third string 23 is controlled by drive circuit 34. It should be apparent to those skilled in the art that the LED strings may also be arranged horizontally or in other ways.

[0007] There are many parameters in an LED string that can be controlled to optimize the efficiency and / or other operating objectives of an LED string and a driver. These include temperature, luminous intensity, luminous color, current, and voltage. For example, current is an important factor for displays because the current in the LEDs determines the brightness or luminous intensity of the LEDs. The intensity (or brightness) of an LED depends on the current flowing through the LED. The curve diagram of Fig. 3 represents the luminous intensity as a function of the forward current of an LED. As the current in the LED increases, the intensity of the light produced by the LED also increases. The current in the LED must be sufficiently high to provide the desired brightness. However, to ensure efficient operation and avoid excessive power loss, the current should not be too high.

[0008] A device for controlling an LED backlight with an LED array is known from publication KR 10 2007 0 109 049 A. Control is achieved, among other things, using a constant current and pulse-width control based on measurements of the state of the LED array.

[0009] US 2007 / 0 040 512 A1 discloses a digitally controlled lighting system designed to emit light with a desired chromaticity and luminous flux in continuous operation at varying ambient temperatures. The control is based on optical signals obtained with an optical sensor system that detects the chromaticity and luminous flux of the emitted light. A thermal sensor system is also present. Parameters, including forward voltages, are measured for each of a plurality of arrays of light-emitting elements.

[0010] From the document US 2008 / 0 042 045 A1 an electro-optical device is known which comprises a plurality of electro-optical elements (for example: LED elements) for which a correction control is carried out in order to limit a variation of the light intensity of each individual electro-optical element. Summary of the invention

[0011] The present invention relates to circuit assemblies and methods for controlling one or more LEDs or LED drivers. The circuit assembly includes a programmable, decentralized controller coupled to one or more detectors, wherein the one or more detectors are configured to detect one or more measurable parameters of the one or more LEDs or LED drivers. The controller is configured to receive information from the one or more detectors regarding the one or more measurable parameters. The controller is further configured to adjust one or more controllable parameters until one or more detectors detect that one or more measurable parameters in one of the LEDs or LED drivers meet a reference condition.The controller is further configured to then set one or more of the controllable parameters for operation at a value relative to the value of the controllable parameters at which the reference condition is met.

[0012] The present invention further provides a method for controlling one or more LEDs or LED drivers. The method comprises: detecting one or more measurable parameters of the one or more LEDs or LED drivers; receiving information from the one or more detectors relating to the one or more measurable parameters; adjusting one or more controllable parameters of the one or more LEDs or LED drivers until the measurable parameters in the one or more LEDs or LED drivers satisfy a reference condition; and setting the controllable parameters to operate at a value relative to the value of the controllable parameters at which the reference condition is satisfied, wherein the adjustment is performed by a programmable, decentralized controller. Brief description of the drawings

[0013] The above and other objects and advantages of the present invention will become more apparent from the following description with reference to the accompanying drawings, wherein like reference numerals are used to refer to corresponding parts throughout. Fig. 1 shows an example display with LED chains. Fig. 2 shows another example display with LED chains. Fig. Figure 3 is a graph showing the relationship between current and luminous intensity in an LED. Fig. 4 shows the use of an embodiment of the control device according to the present invention. Fig. 5 shows the use of an embodiment of the control device according to the present invention. Fig. 6 shows the use of an embodiment of the control device according to the present invention. Fig. 7 shows the use of an embodiment of the control device according to the present invention. Detailed description of the invention

[0014] The present invention relates to circuit assemblies and methods for controlling one or more LEDs or LED drivers. The circuit includes a programmable, decentralized controller coupled to one or more detectors, wherein the one or more detectors are configured to detect one or more measurable parameters of one or more LEDs or LED drivers. The controller is configured to receive information from the one or more detectors regarding the one or more measurable parameters. The controller is further configured to adjust one or more controllable parameters until one or more detectors indicate that one or more measurable parameters in one of the LEDs or LED drivers meet a reference condition.The control device is further configured to then set one or more of the controllable parameters for operation at a value relative to the value of the controllable parameters at which the reference condition is met.

[0015] The present invention further provides a method for controlling one or more LEDs or LED drivers. The method comprises: detecting one or more LEDs or LED drivers; receiving information from the one or more detectors relating to the one or more measurable parameters; adjusting one or more controllable parameters of the one or more LEDs or LED drivers until the measurable parameters in the one or more LEDs or LED drivers satisfy a reference condition; and setting the controllable parameters for operation at a value relative to the value of the controllable parameters at which the reference condition is satisfied, wherein the setting is performed by a programmable, decentralized controller.

[0016] "Relative to" here means: if a value A is set relative to a value B, the value A is a function of the value B. The functional relationship between A and B can be defined mathematically or by reference to a theoretical or empirical relationship. And coupling here means a direct or indirect series connection through wires, conductors, or other connecting elements. Coupled elements can receive signals from each other.

[0017] Fig. Figure 4 shows a configuration in which circuit 42 can be used to control at least one parameter in a load 43 or a load driver 44 of the present invention. The load 43 can be a chain or array of LEDs, and the driver 44 can be a driver for a chain or array of LEDs. Fig. 4, a detector 41 is coupled to the load 43 and / or the driver 44. The detector 43 detects measurable parameters in the load 43 and / or the driver, such as the temperature, voltage, current, luminous intensity, or the wavelength or color of the light. The triode region detector of US patent application Ser. No. 12 / 111,114, which is incorporated herein by reference in its entirety, is an example of a detector that can be used in conjunction with the driver 42 of the present invention. The load 43 is connected to a power supply 40 that provides the drive voltage for the LED string 43. The load 43 is also coupled to a driver 44 that regulates the operation of the load 43. The driver 42 is coupled to the power supply 40 so that the driver 42 can control the drive voltage from the power supply 40. As shown in Fig. 4, the programmable controller 42 of the present invention is decentralized. That is, the controller 42 is not a necessary part of the control loop or the power supply loop, but can influence the power supply loop. In the example of Fig. 4, the power supply 40 can be initiated and the driver 44 can drive the load 43 to a set operating condition without requiring interaction with the programmable, decentralized controller 42. Therefore, the control loop, which includes the power supply 40, the load 43, and the driver 44, can operate independently of the controller 42. However, when an event occurs or a certain interval expires, the programmable, decentralized controller can adjust the operation of the driver loop to calibrate and / or optimize a parameter of the driver loop.

[0018] In the following example, the detector 41 is a triode region detector. However, this is merely an example, and the invention is by no means limited thereto. If the detector 41 is a triode region detector coupled to an LED driver 44, the controller 42 is configured to control the driver 44 and / or the power supply 40 to gradually decrease the drive voltage until the triode region detector 41 sets a triode region flag. The controller 42 then causes the power supply 40 and / or the driver 44 to operate with a drive voltage that is a certain programmable amount above the drive voltage at which the triode flag was set.The control device 42 causes the power supply 40 and / or the drive device 44 to set the drive voltage sufficiently high to avoid operation in the triode region, thereby optimizing the power loss in the circuitry and improving the efficiency of the circuitry.

[0019] In the example described above, the control device 42 causes the power supply 40 and / or the drive device 44 to gradually decrease the drive voltage. However, the control device 42 can also cause the power supply 40 and / or the drive device 44 to gradually increase the drive voltage in accordance with the application in which the control device 42 is used. Furthermore, the control device 42 can also control other controllable parameters such as current, power, or resistance depending on the application. And in addition to gradually increasing or decreasing the drive voltage, the control device 42 can also wait for the drive voltage or another controllable parameter to be increased or decreased until a reference condition is met.In the example described above, the controller 42 causes the power supply 40 and / or the driver 44 to set the drive voltage sufficiently high to avoid operation in the triode region. Depending on the application of the controller 42, the controller 42 may also cause the power supply 40 and / or the driver 44 to set the drive voltage to any point relative to the drive voltage at which the reference condition detected by the detector 41 is met. The reference condition may be constantly offset from the sensed parameter such that the reference condition is met when the sensed parameter is within a positive or negative constant of a particular reference for the sensed parameter. The reference condition may be a function of the sensed parameter and a reference parameter.The reference condition can also be a function of several measured parameters such as a combination of voltage, wavelength and intensity.

[0020] As in Fig. As shown in Figure 5, in one embodiment, controller 52 may include a digital-to-analog converter ("DAC") and a state machine. The programmable controller of the present invention may be programmed and implemented in analog and / or digital form as hardware, software, and / or firmware.

[0021] As in Fig. 6, the programmable, decentralized controller 66 may be coupled to one or more detectors 63, 64, 65, which in turn are coupled to one or more loads or drivers 60, 61, 62. In this embodiment, the power supply 67 is coupled to one or more loads and drivers 60, 61, 62. The controller operates as explained above and causes the power supply 67 and / or the drivers 60, 61, 62 to adjust a controllable parameter until at least one of the detectors 63, 64, 65 detects that a reference condition is met in the loads and / or drivers 60, 61, 62 to which the detector is coupled.The control device 66 can cause the power supply 67 and / or the control devices 60, 61, 62 to be operated with a setting of the controllable parameter relative to the value of the controllable parameter at which the reference condition is met in at least one of the loads or control devices 60, 62, 62. Detection of the fulfillment of the reference condition in one of the loads or control devices 60, 61, 62 or in a specific combination of several of the loads or control devices 60, 61, 62 can serve as the trigger for the control device 66 to cause the power supply 67 and / or the control devices 60, 61, 62 to set the controllable parameters. The control device 66 may provide a delay from the time at which the reference condition is met in one of the loads or control devices 60, 61, 62 until the time at which the controllable parameter is set.

[0022] As in Fig. 7, the control device 706 of the present invention may be used in conjunction with one or more other control devices 709. In the example of Fig.7, an integrated circuit chip 710 includes the controller 706 and the detectors 703, 704. The integrated circuit chip 710 further includes a controller 709, a detector 705, and a driver 702. A second integrated circuit chip 711 includes the controller 709 and the detector 705. The detectors 703, 704, 705 are coupled to loads and drivers 700, 701, 702, respectively. The loads and drivers 700, 701, 702 are connected to a power supply 707. The controllers 706, 709 may be coupled to a system for inter-chip communication ("SIC") 708, as described in U.S. patent application Ser. No. 12 / 046,280, which is incorporated herein by reference in its entirety.When the detectors 703, 704, 705 detect that a reference condition is met in one of the corresponding loads and / or drivers 700, 701, 702 or in a particular combination of loads and drivers 700, 701, 702, at least one of the control devices 706, 709 causes the power supply 707 to set the controllable parameters in the loads and drivers 700, 701, 702.

[0023] The control device can set the controllable parameter at a regular or adjustable interval or upon the occurrence of certain events, such as during initial start-up or upon changes to certain system parameters. The control device can set the controllable parameter upon a change in a second measurable parameter in at least one of the one or more loads and / or drive devices. The second measurable parameter can be identical to the measurable parameter detected by the detectors or can be a different measurable parameter. The control device can be integrated into a liquid crystal display with LEDs.

[0024] It should be apparent to those skilled in the art that the techniques, structures, and methods described herein are merely exemplary of the invention. The invention may be implemented in various other forms without departing from the scope of the invention.

Claims

[1] Circuitry for controlling one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702), the circuitry comprising: a programmable control device (42; 52; 66; 706, 709) coupled to one or more detectors (41; 51; 63, 64, 65; 703, 704, 705), wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) are configured to detect one or more measurable parameters of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702), wherein the control device (42; 52; 66; 706, 709) is configured to receive information from the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) relating to the one or more measurable parameters, characterized by , that the control device (42; 52; 66; 706, 709) is decentralized, the control device (42; 52; 66; 706, 709) is configured to adjust one or more controllable parameters until one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) indicate that one or more parameters in one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702) satisfy a reference condition, and wherein the controller is configured to set one or more of the controllable parameters to operate at a value that is a function of the value of the controllable parameters at which the reference condition is satisfied. [2] Circuit assembly according to claim 1, wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) detects the ambient temperature of at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [3] The circuit assembly of claim 1, wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) detects the current in at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [4] The circuit assembly of claim 1, wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) detects the voltage in at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [5] Circuit assembly according to claim 1, wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) detects the luminous intensity of at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702). [6] The circuit assembly of claim 1, wherein the one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) detects the wavelength of the light emitted by at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702). [7] Circuit construction according to claim 1, wherein the control device (42; 52; 66; 706, 709) initiates the setting of the controllable parameters upon starting at least one of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702). [8] Circuit construction according to claim 1, wherein the control device (42; 52; 66; 706, 709) initiates the adjustment of the controllable parameters upon a change in a second measurable parameter in at least one of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702). [9] Circuit construction according to claim 1, wherein the control device (42; 52; 66; 706, 709) initiates the setting of the controllable parameters with a fixed or variable time interval. [10] Circuitry according to claim 1, wherein the control device (52) comprises a digital-to-analog converter and a state machine. [11] A liquid crystal display comprising the circuit structure of claim 1. [12] A method for controlling one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702), the method comprising: Detecting one or more measurable parameters of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702), Receiving information from one or more detectors (41; 51; 63, 64, 65; 703, 704, 705) relating to the one or more measurable parameters, characterized by Adjusting the one or more controllable parameters of the one or more LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices until the measurable parameters in the one or more LEDs or LED control devices (44; 54; 60, 61, 62; 700, 701, 702) satisfy a reference condition, and Setting the controllable parameters for operation at a value which is a function of the value of the controllable parameters at which the reference condition is satisfied, the setting being carried out by a programmable, decentralized control device (42; 52; 66; 706, 709). [13] The method of claim 12, wherein the reference condition is based on the ambient temperature of at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [14] The method of claim 12, wherein the reference condition is based on the current in at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [15] The method of claim 12, wherein the reference condition is based on the voltage in at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED drivers (44; 54; 60, 61, 62; 700, 701, 702). [16] The method of claim 12, wherein the reference condition is based on the luminous intensity of at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702). [17] The method of claim 12, wherein the reference condition is based on the wavelength of the light emitted by at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702). [18] Method according to claim 12, wherein the setting of the controllable parameters is initiated upon starting of at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702). [19] Method according to claim 12, wherein the adjustment of the controllable parameters is initiated upon a change in the parameters in at least one of the LEDs (43; 53; 60, 61, 62; 700, 701, 702) or LED control devices (44; 54; 60, 61, 62; 700, 701, 702). [20] Method according to claim 12, wherein the adjustment of the controllable parameters is initiated with a fixed or variable time interval.

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