Method and apparatus for controlling driving current of illumination source in a display system

Method and device for controlling driving current of luminous light source in display system

This creation is about a current stabilizer, and more to say, a programmable current stabilizer for the luminous source of a liquid crystal display.

Generally, liquid crystal display (LCD) components are used in various applications, such as notebook computers, mobile phones, personal digital assistants, car dashboards, and so on. Typically, the light source is located in the light modulator in the LCD element, such as behind the liquid crystal layer to facilitate viewing images and produce the best light-emitting effect. The light source can be fluorescent lamps, electroluminescent elements, light emitting diodes (LED), gaseous discharge lamps, etc. Generally, the control circuit provides the rectified current to the light source.

FIG. 1 illustrates a conventional rectifier 100 used for the light-emitting source 104. The light source module 104 may be located behind the light modulator in the LCD element. The light source module 104 includes light emitting diodes (LEDs) connected in series. The LED current control integrated circuit (also referred to as a controller) 102 controls the driving current of the light source module 104. The output terminal DRV of the controller 102 is connected to the bottom of the transistor 108 via the RC filter 106. The collector of the transistor 108 is connected to the power supply Vcc via the connector load resistance 110. The emitter of the anamorphic crystal 108 is grounded. The collector of the transistor 108 is further connected to the light source module 104 via the diode 112. The output terminal of the light source module 104 is grounded through the bias resistor 114. The output terminal of the light source module 104 is also connected to the terminal FB of the controller 102. The capacitor 116 grounds the power supply Vcc. Another capacitor 118 connects the diode 112 to ground.

In another conventional rectifier 100, the bias resistor 114 determines the value of the driving current that can flow through the light-emitting light source module 104. The controller 102 outputs a fixed start signal to the bottom of the transistor 108 through the RC filter 106. The transistor 108 provides a predetermined driving current to the light-emitting source module 104. Typically, once the resistance value of the bias resistor 114 is established, the driving current through the light source module 104 cannot be adjusted. The luminosity of the LED of the light-emitting source module 104 is proportional to the driving current flowing through the light-emitting source module 104. Long-term use of the circuit components may cause unexpected changes in the driving current of the light source module 104. In addition, the driving current in certain types of LEDs, such as organic LEDs (OLEDs), may change due to changes in the operating temperature of the rectifier 100. As a result, the luminosity of the LEDs in the light source module 104 may be unfavorable. Therefore, there is a need for a method and device for controlling the driving current of the light-emitting source module in the LCD system.

The present invention describes a method and system for providing adjusted driving current of a light source. The light source may include a backlight source for LCD systems, such as an LED backlight source for small LCD systems. LED backlight sources can include various LEDs, such as white LEDs, color LEDs, and organic LEDs (OLED). In one embodiment, the rectifier provides a regulated operating driving current for the light source. The predetermined reference drive current is programmed in a memory as a digital reference value. The digital reference value is converted into a corresponding first electrical parameter (voltage or current). The comparator compares the first electrical value with a second electrical value (voltage or current) corresponding to the operating driving current flowing through the light-emitting source. The comparator generates a bias drive current of the rectifier according to the comparison result. The rectifier then adjusts the operating drive current of the light source accordingly. The rectifier provides a light source with a substantially fixed operating driving current in various environments and operating conditions.

FIG. 2A shows a controller 200 that provides a light-emitting source 214 and a programmable driving current according to an embodiment of the present invention. The controller 200 includes a power supply 210 for providing a light source 214 and a driving current. The light source 214 may include a backlight source used in an LCD system, such as an LED backlight source used in a small LCD system. The rectifier 212 is connected to the power supply 210 and the light source 214. The rectifier 212 is used to provide a regulated driving current of the light source 214. The rectifier 212 may be a resistor, such as a metal oxide semiconductor transistor. The current sensor 216 is connected to the light source 214. The current sensor 216 is used to measure the driving current flowing through the light-emitting source 214.

The comparator 218 is connected to the current sensor 216. The comparator 218 is also connected to the signal reference unit 224. The comparator 218 is used to compare the operating driving current measured by the current sensor 216 with the reference signal (current or voltage) provided by the signal reference unit 224. According to the comparison result, the comparator 218 generates an error signal representing the difference between the operating driving current and the reference signal. The programmable interface unit 220 is used to provide a signal difference representing a reference signal. The digital reference value is converted into an analog signal by a digital-to-analog converter 222 connected to the programmable interface unit 220. The signal reference unit 224 uses the analog signal generated by the digital-to-analog converter 222 to generate a reference signal.

The programmable interface unit 220 may include any programmable controller, such as a microprocessor, an application specific integrated circuit, a digital signal processor, and so on. The user can program the digital difference value in the programmable interface unit 220 to provide a specific reference driving current value for the light-emitting light source 214. In addition, the programmable interface unit 220 can also improve the digital reference value programmed by the user. For example, the programmable interface unit 220 can be programmed to monitor the environment and operating conditions of the controller 200 and adjust the digital reference value accordingly. The comparator 218 uses the error signal to adjust the input bias of the rectifier 212. The rectifier 212 adjusts the operating driving current of the light source 214 according to the input bias value.

FIG. 2B illustrates a controller 260 that uses a voltage comparator 235 to provide a programmable and adjusted driving current of the light source 214 according to an embodiment of the present invention. The controller 260 includes a programmable interface unit 220. The programmable interface unit 220 is connected to a register 226. The register 226 is a data storage unit for storing the functional parameters of the light-emitting source 214. For illustration, the register 226 is shown as an independent data storage unit, however, the register 226 may be incorporated into the programmable interface unit 220.

The programmable interface unit 220 is connected to the digital-to-analog converter 222. The digital-to-analog converter 222 converts the digital reference value stored in the register 226 into a corresponding analog signal. The user can use the programmable interface unit 220 to program the digital reference value in the register 226. The digital reference value represents the reference driving current of the light-emitting light source 214. The digital reference value can be obtained by simulating the required operating conditions of the light-emitting source 214. For example, if the luminosity of the light-emitting source 214 is proportional to the driving current flowing through the light-emitting source 214, the optimal driving current value corresponding to the luminosity required by the light-emitting source 214 can be obtained by simulating the operating conditions of the luminosity required by the light-emitting source 214. Then the preferred driving current value can be converted into a digital reference value by an analog-to-digital converter and stored in the register 226.

The programmable interface unit 220 provides a digital reference value to the digital-to-analog converter 222. The digital-to-analog converter 222 converts the digital reference value into an analog signal and transfers the analog signal to a voltage reference unit 230. The voltage reference unit 230 is used to generate a reference voltage signal corresponding to the analog signal. For the sake of illustration, the voltage reference unit 230 is shown as an independent unit, however, the voltage reference unit 230 can be combined into a digital-to-analog converter 222. For example, the digital-to-analog converter 222 can be used to convert a digital reference value into a reference voltage signal. The voltage comparator 235 is connected to the voltage reference unit 230. The voltage comparator 235 is used to compare two input voltage values and generate a driving signal DRV corresponding to the difference between the two input voltages.

The rectifier 212 is connected to the voltage comparator 235. The rectifier 212 is further connected to the light source 214. In this embodiment, the rectifier 212 includes a metal oxide semiconductor (MOS) transistor 240. The MOS transistor 240 is used to adjust the driving current of the light source 214. The gate terminal of the MOS transistor 240 and the voltage comparator 235 also receive the driving signal DRV. The source terminal of the MOS transistor 240 is grounded, and the drain terminal of the MOS transistor 240 is further connected to the light source 214 via the diode D. The diode D is also grounded via the bypass capacitor C. The diode D is used to protect the light-emitting source 214 from malfunction of the controller 260, and to divert an unwanted high-frequency current through the bypass capacitor C to ground.

In this embodiment, the light source 214 includes a number of LEDs 242(1)-(n) connected in series. LED 242 (1)-(n) can be connected in series, parallel, or a combination of series and parallel connections. The sensor 216 is connected to the light source 214. The inductor 216 includes an inductor resistor Rs. The sensor resistance Rs is used to measure the voltage FB corresponding to the driving current flowing through the light-emitting source 214. The sensor resistance Rs is connected to one of the input terminals of the voltage comparator 235. The voltage comparator 235 receives the voltage FB and compares it with the reference voltage signal from the voltage reference unit 230, and generates a driving signal DRV for the gate terminal of the MOS transistor 240.

The driving signal DRV drives the gate terminal of the MOS transistor 240 according to the difference between the voltage FB and the reference voltage signal. The MOS transistor 240 adjusts the driving current of the light-emitting source 214 according to the driving signal DRV. For example, if the driving current in the light-emitting source 214 decreases due to certain operating and environmental factors, the difference between the voltage FB and the reference voltage signal will generate a The relatively strong driving signal DRV causes the driving current of the light-emitting source 214 to increase. Similarly, if the driving current flowing through the light-emitting source 214 increases, the voltage comparator 235 generates a relatively weak driving signal DRV, which causes the driving current of the light-emitting source 214 to decrease. The values of resistance RL and Rs can be selected according to the driving current required by the light source and the corresponding luminosity.

FIG. 2C shows a schematic diagram of a controller 270 that uses a current detector 237 to provide a light-emitting source 214 with a programmable driving current according to an embodiment of the present invention. The controller 270 includes a programmable interface unit 220, a register 226, and a digital-to-analog converter 222. The current reference unit 232 is connected to the digital-to-analog converter 222 and the current detector 237. The current reference unit 232 is used to provide the current detector 237 with a reference current signal. For illustration, the current reference unit 232 is shown as an independent unit, however, the current reference unit 232 can be incorporated into the digital-to-analog converter 222. For example, the digital-to-analog converter 222 can be used to convert digital reference data into a reference current signal.

The current detector 237 is used to detect the difference between the reference current and the driving current flowing through the light-emitting source 214 and generate the driving signal DRV of the rectifier 212. The function of the current detector 237 is known to those who are familiar with the art. In this embodiment, the inductor 216 includes a sensing resistor Rs and a pair of MOS transistors 252a and 252b. The gate terminals of MOS transistors 252a and 252b are grounded. The drain terminal of the MOS transistor 252b is connected to the gate terminal. The drain terminal of the MOS transistor 252a is connected to the current detector 237.

When the driving current flowing through the light-emitting source 214 changes, the voltage FB across the sensor resistance Rs will also change accordingly. The change of the voltage FB causes the gate bias voltage of the MOS transistors 252a and 252b to change, so that the current flowing through the drain terminal of the MOS transistor 252a changes. When the current detector 237 detects that the current flowing through the MOS transistor 252b is different from the reference current signal, the current detector 237 generates a driving signal DRV corresponding to the difference. The driving signal DRV adjusts the driving current of the rectifier 212 as described above.

FIG. 3A shows a two-bit serial bus interface controller 310 according to a specific embodiment of the present invention, which is used to provide a controller for a programmable driving current of a light source. The controller 310 is a two-bit interactive integrated circuit (I2C) programmable serial bus interface that complies with industry standards. The controller 310 includes two-way signal lines, Clock (SCL) and Data (SDA), for communication with integrated circuit components. The SCL signal line is used for serial clock counting, and the SDA signal line is used for serial data. The I2C programmable serial bus interface can be used for applications that need to reduce the number of controller pins. I2C-type controllers can provide bus speeds up to 400kHz.

FIG. 3B shows a specific embodiment of the present invention. The typical data row 315 format of the I2C two-bit serial bus interface controller shown in FIG. 3A is shown. The I2C controller operates according to the master/slave relationship between various integrated components. The master integrated device is a device that controls the SCL line, starts and stops data transfer, and controls the addressing of other devices connected to the I2C controller. A slave integrated device is a component selected by a master control component. A typical data row 315 includes a start bit S, seven address bits, one read/write bit, three confirmation bits A, two data bytes, and one stop bit P. Typically, the data receiving component sets the confirmation bit to indicate whether the data is received. Once the last bit of the 8-bit data has been transferred, a confirmation flag A is set to confirm that no error occurred during the data transfer. The I2C controller transfers the data from the largest bit to the smallest bit.

FIG. 3C shows a specific embodiment of a three-wire serial bus interface controller 350 of the present invention. The serial bus interface controller 350 can be used as a programmable current controller for providing the adjusted driving current of the light source. The controller 350 is a three-wire serial bus interface controller compliant with industry standards. The controller 350 includes three-tone two-way signal lines-Clock (SCLK), Data In/Out (I/O), and Chip Select (CS). The CS signal line is used to select specific components for lighting, the I/O signal line is used for data/address transfer, and the SCLK signal line is used to synchronize data transfer. The three-wire controller can provide bus speeds up to 5MHz.

FIG. 3D is a clock diagram of the unit tuple data transfer protocol of the three-wire serial bus interface controller 350 shown in FIG. 3C. The data transfer in the controller 350 is controlled by the CS signal. The CS signal must be at a high level during all data transfers. When starting any data transfer, the SCLK signal should be low level. Data is counted into the clock via the I/O signal line on the upper edge of the SCLK signal, and not counted into the clock on the lower edge of the SCLK signal. Similarly, a burst protocol can also be used by the controller 350 to transfer more than one byte in a single data processing. Compared with the I2C controller 310, the three-wire serial bus interface controller 350 transfers data from the smallest bit to the largest bit for data transfer. For the sake of explanation, two serial bus interfaces are described. However, those who are familiar with the art understand that any bus interface controller (serial connection, parallel connection or combination) can also be used to program various components to provide display The adjusted driving current of the light-emitting source in the device.

FIG. 4 is a flowchart of the execution steps of adjusting the driving current flowing through the light-emitting source. For the purpose of illustration, in this embodiment, the steps are executed in a specific order. However, if the steps are executed in an appropriate circuit, the above steps may be executed without limitation to the specific order, and may be performed simultaneously or sequentially in any order.

At the beginning, the reference electrical parameter (voltage or current) of the luminescence source is determined (step 410). The reference electrical parameter represents the predetermined reference driving current of the light source. The type of reference electrical parameters depends on whether the voltage comparator or current detector is used for a particular purpose. According to an embodiment of the present invention, the reference electrical parameter can be determined by simulating the amount of driving current flowing through the light-emitting source. The reference electrical parameter is then converted into a digital reference value using an analog-to-digital converter and programmed in the controller (step 420).

Then, a driving current is provided to the light-emitting source for normal operation (step 430). Then, the electrical parameters (current or voltage) across the light-emitting source are measured to determine the driving current flowing through the light-emitting source (step 440). Then, the measured electrical parameters are compared with the corresponding reference electrical parameters (step 450). The method then determines whether there is a difference between the measured electrical parameter and the reference electrical parameter (step 460). If there is a difference between the measured electrical parameter and the reference electrical parameter, the driving current flowing through the light-emitting source is adjusted according to the difference (step 470).

The driving current flowing through the light-emitting element can be set to almost a constant value by programming an appropriate reference value for parameter comparison. The dynamic current, which is almost constant, maintains the luminosity of the light source and compensates for changes in operation or environment, such as an increase in operating temperature and changes in characteristic bias caused by long-term use of circuit components. According to an embodiment of the present invention, the above-mentioned programmable current controller can be incorporated into a general integrated circuit to provide LCD system backlight module driving current control. In another embodiment, the programmable current controller can be incorporated into the source driver block of the LCD system.

FIG. 5A is a block diagram of a programmable drive current controller that operates the source driver block incorporated in the LCD system 500 according to an embodiment of the present invention. The LCD system 500 includes an LCD panel 505. The LCD panel 505 includes a gate driver 510 and a source driver 515. The gate driver 510 and the source driver 515 are used to provide driving signals to the row and column elements of the display panel 505. The source driver 515 includes a programmable drive current controller ("controller") 520. The controller 520 is connected to a rectifier 530 and a light source 540. In this embodiment, the controller 520 uses a voltage comparator (not shown), however. The controller 520 can also utilize a current detector, as described above. The sensor resistance Rs is used to measure the voltage representing the driving current flowing through the light-emitting element. For the sake of illustration, the light source 540 is used as the backlight module of the LCD panel 505 and includes two LEDs 542a and 542b. However, the light-emitting source 540 may include any number of LEDs, light sources, and other similar light-emitting elements. The rectifier 530 includes a MOS transistor 535 and a load resistor R_L, A protection diode D, a voltage source Vcc, and a bypass capacitor C. The function of the rectifier 530 is as described above.

FIG. 5B is a schematic diagram of the controller 520 in the source driver block 515 of the liquid crystal display system 500 according to a specific embodiment of the present invention. The controller 520 includes a programmable interface unit 522, a digital-to-analog converter 524, and a voltage comparator 526. In this embodiment, the digital-to-analog converter 524 provides the voltage comparator 526 with a reference voltage. The voltage comparator 526 compares the reference voltage from the digital-to-analog converter 524 with the voltage FB from the inductor resistor Rs. For comparison, the voltage comparator 526 provides the driving bias signal DRV to the rectifier 530. Any change in the driving current flowing through the light-emitting source 540 is reflected in the driving bias signal DRV, and is used to adjust the driving current of the light-emitting source 540.

Although this creation has been described with reference to the preferred embodiments, it will be understood by us that this creation is not limited to its detailed description. The replacement methods and modified styles have been suggested in the previous description, and other replacement methods and modified styles will be thought of by those who are familiar with this art. In particular, according to the device structure of this creation, all the components that have substantially the same combination of components that achieve the same result as this creation will not depart from the spirit of this creation. Therefore, all these alternatives and modifications are intended to fall within the scope of the present invention as defined by the scope of the attached patent application and its equivalents.

<p><u style="single">Known technology:</u></p><p>104Light source</p><p>100rectifier</p><p>102LED current control integrated circuit (controller)</p><p>106RC filter</p><p>108Transistor</p><p>110Load resistance</p><p>112Diode</p><p>114Bias resistor</p><p>116,118Capacitor</p><p><u style="single">this invention:</u></p><p>200controller</p><p>210Power Supply</p><p>212rectifier</p><p>214Light Source</p><p>216Current sensor</p><p>218Comparator</p><p>200, 260, 270controller</p><p>220Programmable Interface Unit</p><p>222Digital to Analog Converter</p><p>224Signal Reference Unit</p><p>226register</p><p>230Voltage Reference Unit</p><p>232Current Reference Unit</p><p>235Voltage Comparator</p><p>237Current Detector</p><p>DRVDrive signal</p><p>240Metal Oxide Semiconductor (MOS) Transistor</p><p>DDiode</p><p>242LED</p><p>Rs, RLInductor resistance</p><p>FBVoltage</p><p>252a, 252bMOS Transistor</p><p>237Current Detector</p><p>310Two-bit serial bus interface controller</p><p>315Data row</p><p>350Three-wire serial bus interface controller</p><p>500LCD System</p><p>505LCD Panel</p><p>510Gate Driver</p><p>515 to the source driver</p><p>520Programmable drive current controller ("controller")</p><p>522Programmable Interface Unit</p><p>524Digital to Analog Converter</p><p>526Voltage Comparator</p><p>530rectifier</p><p>540Light-emitting element</p><p>RsSensor resistance</p><p>542a, 542bLED</p><p>535MOS Transistor</p><p>RLLoad resistance</p><p>DProtection diode</p><p>VccVoltage source</p><p>CBypass capacitor</p><p>Step 410Measure the reference electrical parameters (voltage or current) of the luminous source</p><p>Step 420Refer to the electrical parameters and then use an analog-to-digital converter to convert to a digital reference value, and set it into the controller</p><p>Step 430Provide driving current to the light-emitting source for normal operation</p><p>Step 440Measure the electrical parameters (current or voltage) across the luminous source to determine the driving current flowing through the luminous source</p><p>Step 450Compare the measured electrical parameters with the corresponding reference electrical parameters</p><p>Step 460 Determine whether there is a difference between the measured electrical parameter and the reference electrical parameter</p><p>Step 470If there is a difference between the measured electrical parameter and the reference electrical parameter, adjust the driving current flowing through the light-emitting source according to the difference</p>

Fig. 1 is a schematic diagram of a conventional rectifier used for a light-emitting source; Fig. 2A is a block diagram of a controller for providing a programmable driving current for providing a light-emitting source according to an embodiment of the present invention; Fig. 2B is In accordance with an embodiment of the present invention, a schematic diagram of a controller that uses a voltage comparator to provide a light-emitting source with programmable driving current; FIG. 2C is a specific embodiment of the present invention, a current detector to provide light-emitting A schematic diagram of a controller with programmable source of driving current; FIG. 3A is a schematic diagram of a two-bit serial bus interface controller according to an embodiment of the present invention, in which the two-bit serial bus interface controller is constituted A controller for providing a luminous source that can be programmed to adjust the driving current; FIG. 3B shows a data row format of a binary serial bus interface controller shown in FIG. 3A according to an embodiment of the present invention; FIG. 3C It is a schematic diagram of a three-wire serial bus interface controller according to an embodiment of the present invention, wherein the three-wire serial bus interface controller constitutes a controller for providing a luminous source that can be programmed to adjust the driving current; Figure 3D Illustrates the timing diagram of the unit metadata transfer protocol of the three-wire serial bus interface controller shown in FIG. 3C; FIG. 4 is a flowchart of a method for adjusting the driving current flowing through the light-emitting source according to a specific embodiment of the present invention; 5A is a schematic diagram of a programmable drive current controller that can integrate a source driver block of a liquid crystal display system according to an embodiment of the present invention; and FIG. 5B is a source driver block that can integrate a liquid crystal display system shown in FIG. 5A Schematic diagram of the programmable controller.