LED driving circuit and driving method ot thereof.

Abstract

The present embodiment relates to an LED driving circuit for controlling the voltage of an LED backlight system, and more specifically, to a technology for controlling the magnitude of the driving voltage of an LED string formed at one end of the LED string through a digital counter by monitoring the output voltage of an LED string.

Description

Technology Field

[0001] The present embodiment relates to an LED driving circuit and a display device including the same. Background Technology

[0002] As the information age advances, various display devices capable of visualizing information are being developed. Liquid Crystal Displays (LCDs), Organic Light Emitting Diodes (OLEDs), and Plasma Display Panels (PDPs) are representative examples of display devices that have been developed or are currently being developed. These display devices are evolving to properly display high-resolution images.

[0003] In LED display technology, a single large panel can be constructed by arranging modularized LED pixels in the required number. Alternatively, in LED display technology, a large panel structure can be formed by arranging unit panels composed of multiple LED pixels in the required number. In this way, LED display technology makes it easy to implement large display devices by expanding and arranging LED pixels as needed.

[0004] LED displays offer advantages not only in terms of large size but also in diversifying panel sizes; LED display technology allows for various adjustments to the horizontal and vertical dimensions depending on the appropriate arrangement of LED pixels.

[0005] Meanwhile, the LED display device can control the output voltage (V_CH) of the LED string formed at one end of the LED and the LED current (I_LED) flowing through the LED by transmitting PWM (Pulse Width Modulation) driving control signals, PAM (Pulse Amplitude Modulation) driving control signals, etc., to the channel terminal of the LED.

[0006] To finely control the brightness of the LED, it is necessary to control the output voltage (V_CH) and LED current (I_LED) of the LED string, and at the same time, appropriately control the driving voltage (V_LED) of the LED string.

[0007] In particular, by directly turning on and off current sources, transistors, etc., connected to the channels of the LED string, noise that affects the current driving of adjacent channels may be generated, and it is necessary to appropriately reduce the flicker phenomenon caused by changes in the brightness of the LED according to frequency during the LED control process. The problem to be solved

[0008] Against this backdrop, the objective of the present embodiment is to provide an LED driving circuit that controls the output voltage (V_CH) of an LED string or / or controls the driving voltage (V_LED) of an LED string to improve the precision of LED brightness control during the LED driving process, and a display device including the same.

[0009] Another objective of the present embodiment is to provide an LED driving circuit and a display device including the same, which generates a feedback control signal using a digital logic circuit—e.g., a digital counter—when the channel terminal voltage of an LED string is monitored to be below a reference voltage, and controls the output voltage (V_CH) of the LED string or controls the driving voltage (V_LED) of the LED string.

[0010] Another objective of the present embodiment is to provide an LED driving circuit and a display device including the same, which can reduce noise that may affect other channels, such as adjacent LED strings, by controlling the driving voltage of an LED string by a booster converter without directly adjusting the output voltage of the LED string by counting an externally transmitted clock or an internally generated clock through a digital logic circuit to generate a feedback control signal. means of solving the problem

[0011] To achieve the aforementioned objective, in one aspect, the present embodiment comprises: a headroom sensing circuit for sensing the output voltage (V_CH) of an LED string; a digital logic circuit for generating a channel enable signal (CH_EN) of the LED string to control the output voltage (V_CH) of the LED string; and a channel control circuit for controlling the magnitude of the output voltage (V_CH) of the LED string in response to the timing of the channel enable signal (CH_EN) of the digital logic circuit. An LED driving circuit may be provided, comprising a feedback transistor that receives the output voltage of the LED string detected by the headroom sensing circuit, wherein the feedback transistor is electrically connected to a microcontroller unit to control the driving voltage (V_LED) of the LED string, and the microcontroller unit measures the current flowing through the feedback transistor and generates a feedback control signal to control the operation of the boost converter by controlling the magnitude of the driving voltage (V_LED) of the LED string.

[0012] To achieve the aforementioned objective, the present embodiment may provide a headroom sensing circuit that detects an output voltage (V_CH) of an LED string formed at one end of an LED string; a digital logic circuit that determines a feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the headroom sensing circuit determines that the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF); a feedback transistor that receives the output signal of the digital logic circuit at its gate terminal; and a feedback control circuit connected to a first terminal of the feedback transistor and determining whether to adjust the driving voltage (V_LED) of the LED string based on the current value flowing through the first terminal.

[0013] To achieve the aforementioned objective, the present embodiment may provide an LED driving method comprising: a step of monitoring an output voltage (V_CH) of an LED string formed at one end of an LED string and determining whether it is below a reference voltage (V_REF); a step of determining a feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the output voltage (V_CH) of the LED string is below the reference voltage (V_REF); and a step of adjusting the intensity of the driving voltage (V_LED) of the LED string during the feedback timing. Effects of the invention

[0014] As described above, according to the present embodiment, the LED driving circuit can finely adjust the brightness of the LED string by monitoring the output voltage or LED current of the LED string.

[0015] According to the present embodiment, the LED driving circuit can reduce noise such as current changes that may occur in adjacent channels by directly turning on and off the circuit connected to the channel terminal of the LED string, and can eliminate or reduce the flicker phenomenon of the display device.

[0016] According to the present embodiment, the LED driving circuit can implement a Pulse Wide Modulation (PWM) driving waveform by counting an external or internal clock through a digital counter circuit, and can achieve a flicker-free effect by driving at a high PWM frequency without being limited by the display frame rate. Brief explanation of the drawing

[0017] FIG. 1 is a configuration diagram of a display device according to the present embodiment. FIG. 2 is a diagram illustrating a driving method of a display device according to the present embodiment. FIG. 3 is a diagram illustrating a method of supplying power to each channel of a light-emitting diode according to the present embodiment. FIG. 4 is a diagram illustrating the switch operation of the LED driving circuit according to the present embodiment. FIG. 5 is a configuration diagram of a switch circuit according to the present embodiment. FIG. 6 is a method for explaining the control method of the LED driving current according to the present embodiment. FIG. 7 is a first example configuration diagram of an LED driving circuit according to the present embodiment. FIG. 8 is a second example configuration diagram of an LED driving circuit according to the present embodiment. FIG. 9 is a first example timing diagram of signals processed in an LED driving circuit according to the present embodiment. FIG. 10 is a second example timing diagram of signals processed in an LED driving circuit according to the present embodiment. FIG. 11 is a flowchart of an LED driving method according to the present embodiment. Specific details for implementing the invention

[0018] FIG. 1 is a configuration diagram of a display device according to the present embodiment.

[0019] Referring to FIG. 1, the display device (100) may include a System On Chip (SOC) (110), a Timing Controller (T-CON) (120), a data driving circuit (130), a display panel (140), a Micro Controller Unit (MCU) (150), an LED driving circuit (160), a backlight (170), etc.

[0020] The system-on-chip (SOC) (110) may be a circuit that performs the function of a central processing unit (CPU), such as an application processor (AP) of a mobile device, and may also be a semiconductor chip that performs computational and control operations to control the operation of internal electronic circuits of a display device. The system-on-chip (110) may control a timing controller (120), a microcontroller unit (150), etc., or define internal operations by transmitting signals to each circuit.

[0021] The timing controller (T-CON) (120) may be a circuit that controls the operation timing of a data driving circuit (130), an LED driving circuit (160), etc., or performs digital calculations. Additionally, the timing controller (120) may control the data driving circuit (130) to convert image data received from an external source and generate a data voltage corresponding to the grayscale value of a pixel of the display panel (140).

[0022] The data driving circuit (130) can control the operation of the pixel (141) through the data line (DL) by changing the magnitude, waveform, etc. of the data voltage in response to the control signal transmitted by the timing controller (120). For example, the data driving circuit (130) can control the operation of the polarizer placed in the pixel (141).

[0023] The display panel (140) may be an organic light-emitting diode (OLED), a liquid crystal display (LCD), etc., but may have a structure capable of receiving light from a backlight (170). Mini-LED is a miniaturized version of the LED used in the LCD backlight to reduce the disadvantages of conventional LCDs, and requires a chip smaller than the LED driving circuit for conventional LCD operation, and a large number of chips can be used.

[0024] One pixel (P) of the panel (140) forms subpixels such as red (R), green (G), and blue (B), and can determine or change the wavelength of light transmitted through a color filter (not shown).

[0025] A microcontroller unit (MCU) (150) may be a device that transmits control signals to an LED driving circuit (160) to control the driving timing, driving current, driving voltage, etc. of an LED. The timing controller (120) and the microcontroller unit (150) may share some functions and may be implemented in an integrated form for effective data processing as needed, but are not limited thereto.

[0026] The LED driving circuit (160) may be a device for controlling the operation of a plurality of LEDs placed in the backlight. The LED driving circuit (160) may control the operation of a current source or a channel control circuit (not shown) placed inside, and may control the timing of the driving current delivered to the LED or the intensity of the driving current. The LED driving circuit (160) may change the operation of the LED based on a control signal received from the microcontroller unit (150) or may change the operation of the LED based on a signal received from another LED driving circuit. If necessary, the LED driving circuit (160) may change the operation of the LED based on an algorithm or information pre-stored by an internal register (not shown).

[0027] The backlight (170) may be configured such that a plurality of LEDs are arranged on a substrate, and may be formed integrally with the display panel (140) or separately as needed. The LEDs arranged in the backlight (170) may be individually controlled by each LED channel defined as an LED string according to the LED driving circuit (160).

[0028] As used in this specification, the term light-emitting diode (LED) is used interchangeably with LED, and their meanings may be the same.

[0029] FIG. 2 is a diagram illustrating a driving method of a display device according to the present embodiment.

[0030] Referring to FIG. 2, the system-on-chip (SOC) (110) can control the driving of the display panel (140) or the driving of the light-emitting diode (LED) by the timing controller (120) or the microcontroller unit (150).

[0031] The timing controller (120) can determine the operation timing of the gate driving circuit (not shown), the data driving circuit (130), and the LED driving circuit (160), and the operation timing of each circuit can be defined in correspondence with all or part of the rising edge or falling edge of the synchronization signal (SYNC) or the serial clock signal (SCLK).

[0032] The timing controller (120) can control the operation of the pixel (P) by means of a gate control signal (GCS) transmitted to a gate driving circuit (not shown) and a data control signal (DCS) transmitted to a data driving circuit (130). The operation of the liquid crystal polarizer is changed in response to a voltage change of the transistor placed on the display panel (140), and thereby the ratio of transmitted light can be appropriately controlled.

[0033] The microcontroller unit (150) can change the state of the driving voltage or driving current transmitted to the light-emitting diode (LED) by means of the LED control signal (LCS) transmitted to the LED driving circuit (160).

[0034] The timing controller (120) and the microcontroller unit (150) can be implemented with an integrated circuit configuration, or can be defined as functionally separated individual circuit configurations as needed.

[0035] FIG. 3 is a diagram illustrating a method of supplying power to each channel of a light-emitting diode according to the present embodiment.

[0036] Referring to FIG. 3, the backlight (170) can receive a driving voltage (V_LED) to one end of the LED string by a switching mode power supply (SMPS) (180), and can determine the brightness of the light-emitting diode (LED) by allowing a driving current (I_LED) to flow through a current channel (CH1-12).

[0037] The switching mode power supply (180) can supply the same driving voltage (V_LED) or different driving voltages (V_LED1 to V_LED12) to the first LED group (171-1) to the twelfth LED group (171-12), and the LED driving circuit (not shown) can control the driving current (I_LED) flowing through each LED string by adjusting the voltage at the other end of each channel. The LEDs of the LED string can irradiate light to a display panel in response to the driving current (I_LED) to display an image of a desired brightness.

[0038] The switching mode power supply (180) can adjust the magnitude of the driving voltage (V_LED) of the LED string using a boost converter, etc., and can determine the timing and intensity of the driving voltage (V_LED) of the LED string according to a control signal transmitted from the microcontroller unit (150).

[0039] The same driving current (I_LED) may flow through each channel, but different driving currents (I_LED1 to I_LED12) may flow.

[0040] The microcontroller unit (150) can control the timing, size, etc. of the LED driving voltage (V_LED) supplied by the switching mode power supply (180).

[0041] The number and shape of the LEDs and channels formed in the backlight (170) of FIG. 3 are intended to exemplify the driving voltage and driving current of the LEDs, and may include various numbers and shapes of LEDs that are not limited thereto.

[0042] FIG. 4 is a diagram illustrating the switch operation of the LED driving circuit according to the present embodiment.

[0043] Referring to FIG. 4, the LED driving circuit (160) receives an LED driving control signal (CS_LED)—e.g., a PWM driving control signal (CS_PWM), a PAM driving control signal (CS_PAM), etc.—transmitted by the microcontroller unit (150), and can control the brightness of the light transmitted to the display panel by adjusting the timing or intensity of the driving current of the light-emitting diode (LED). The LED driving circuit (160) can also control the brightness of the light-emitting diode (LED) by controlling the timing or intensity of the voltage applied to one or both ends of the channel.

[0044] The LED driving control signal (CS_LED) can define the operation timing of the internal circuit of the LED driving circuit (160), and can individually control the driving current (I_LED) of the light-emitting diode flowing in the channel (CH1, CH2, etc.) by changing the state of the internal transistor of the LED driving circuit (160).

[0045] For example, the LED driving control signal (CS_LED) can control the turn-on and turn-off of a switch placed inside the LED driving circuit (160), or control the strength or direction of the current flowing through the transistor.

[0046] Referring to FIG. 4, the LED driving circuit (160) may further include a channel control circuit (162), and the channel control circuit (162) may further include a first switch circuit (162-1) and a second switch circuit (162-2).

[0047] The LED driving circuit (160) may include one or more current channels (CH) that are electrically connected to a light-emitting diode (LED) and transmit a driving current to the light-emitting diode. For example, a first driving current (I_LED1) can be generated and controlled individually through a first channel (CH1) and a second driving current (I_LED2) through a second channel (CH2).

[0048] The current channel (CH) can be connected in series with a light-emitting diode (LED), a first switch circuit (162-1), and a second switch circuit (162-2). The output voltage (V_CH) or driving current (I_LED) of the light-emitting diode (LED) can be changed by the operation of the first and second switch circuits (162-1, 162-2).

[0049] The dimming control circuit (163) receives a PWM operation control signal (CS_PWM) or a PAM operation control signal (CS_PAM) from the microcontroller unit (150) and can define the operation timing or operation state of the first switch circuit (162-1) and the second switch circuit (162-2). The current channel (CH) may include a plurality of channels, and the dimming control circuit (163) can individually control the light-emitting diode driving current (I_LED1, I_LED2, etc.) of the plurality of channels or the output voltage of the LED string (V_CH1, V_CH2, etc.) in response to the PWM operation control signal or the PAM operation control signal.

[0050] The dimming control circuit (163) can set the operating range of the first switch circuit (162-1) and the operating range of the second switch circuit (162-2) based on the driving current value of the light-emitting diode (LED) or the output current value of the digital-to-analog converter (DAC).

[0051] The first switch circuit (162-1) can adjust the magnitude of the driving current of the light-emitting diode according to the duty ratio of the PWM (Pulse Width Modulation) operation control signal. For example, as the duty ratio of the PWM operation control signal decreases, the time interval of the current passing through the first switch circuit (162-1) decreases, and as a result, the driving current (I_LED) of the light-emitting diode can be reduced. Depending on the turn-on timing and turn-off timing of the first switch circuit (162-1), the driving current (I_LED) of the light-emitting diode can increase or decrease at a constant period, and the average intensity of the driving current of the light-emitting diode can be defined by averaging this.

[0052] The second switch circuit (162-2) can receive a Pulse Amplitude Modulation (PAM) drive control signal and adjust the magnitude of the driving current of the light-emitting diode. The second switch circuit (165) can receive a PAM drive control signal having an analog signal waveform or receive a code value having a digital signal waveform.

[0053] The LED driving circuit (160) individually controls the PWM driving control signal and the PAM driving control signal transmitted to a plurality of current channels, and can receive PWM control data controlling the PWM driving control signal and PAM control data controlling the PAM driving control signal in the same time interval. In this case, the communication protocol can be simplified by receiving the PWM control data and PAM control data simultaneously.

[0054] The microcontroller unit (150) can determine the PWM driving timing and PAM driving timing by time-dividing the LED driving control signal of N bits (N is a natural number greater than or equal to 2). The LED driving control signal may be a control signal for selecting one of a PWM driving mode that performs PWM driving exclusively, a PAM driving mode that performs PAM driving exclusively, and a hybrid driving mode that performs a combination of PWM driving and PAM driving.

[0055] The LED driving circuit (160) monitors the output voltage (V_CH1, V_CH2, etc.) or LED current (I_LED1, I_LED2, etc.) of the LED string detected by the headroom detection circuit (161) in real time or periodically, and transmits it to the microcontroller unit (150) or to a digital logic operation circuit (not shown) inside the LED driving circuit (160) for operation of the LED driving circuit (160).

[0056] The LED driving circuit (160) includes a plurality of integrated circuits electrically connected to a plurality of current channels, and the plurality of integrated circuits are connected in a serial structure to perform serial peripheral interface (SPI) communication so that the driving mode can be updated sequentially. The driving mode of the plurality of integrated circuits or the plurality of current channels is individually defined, and the driving mode can change according to one frame or some frames.

[0057] The LED driving circuit (160) includes a plurality of current channels, and the LED driving control signal can transmit a signal that compensates for current deviation by individually adjusting the driving current of each current channel.

[0058] FIG. 5 is a configuration diagram of a switch circuit according to the present embodiment.

[0059] Referring to FIG. 5, the channel control circuit (162) may include a first switch circuit (162-1) and a second switch circuit (162-2), etc.

[0060] The first switch circuit (162-1) may include a field-effect transistor (T1) having one terminal electrically connected to a current channel, and the transistor (T1) may receive a PWM driving control signal (CS_PWM) through its gate terminal. One terminal of the transistor (T1) is connected to the current channel of an LED string, and the other terminal may be connected to a transistor (T2).

[0061] The first switch circuit (162-1) can change the state of the supply current (I_LED) of the light-emitting diode (LED) by repeating the turn-on state or turn-off state in response to the duty ratio of the PWM driving control signal.

[0062] The second switch circuit (162-2) may include an operational amplifier (AMP) that receives a PAM drive control signal through a first input terminal—e.g., a positive input terminal—a field-effect transistor (T2) that receives an output signal of the operational amplifier through a gate terminal, and a resistor (R) connected to the drain terminal of the transistor (T2).

[0063] Additionally, the operational amplifier of the second switch circuit (162-2) can receive the drain terminal voltage of the transistor (T2) as a feedback voltage through the second input terminal—e.g., a negative input terminal—and can determine an output signal by comparing the voltage difference between the positive input terminal and the negative input terminal.

[0064] FIG. 6 is a method for explaining the control method of the LED driving current according to the present embodiment.

[0065] Referring to FIG. 6, the method for controlling the LED current or the output voltage of the LED string of the LED driving circuit can be such that, as in the first case (CASE 1), the period (S1) of the turn-on state corresponding to a constant period (S2) is defined as the duty cycle and a PWM driving control signal is generated to perform on / off of the current source, or the brightness of the LED can be controlled by changing the LED current (I_LED) or the output voltage (V_CH) of the LED string by adjusting the time interval of the current passing through the transistor.

[0066] As in the second case (CASE 2), the current strength of the LED current can be increased by increasing the current strength of the current source or the current strength passing through the transistor from the first strength (H1) to the second strength (H2). In this case, the brightness of the LED can be changed to be brighter by increasing the signal strength while maintaining the same duty cycle compared to the first case (CASE 1).

[0067] In the third case (CASE 3), the brightness of the LED can be changed by changing the duty cycle while maintaining the first intensity (H1). The magnitude of the LED current of the LED can be increased according to the duration (S1') of the changed turn-on state. By supplying current to the LED for a long time within one cycle, the LED brightness can be increased by increasing the average value of the LED current formed in the LED.

[0068] In addition to the LED current (I_LED), the LED driving circuit may apply the aforementioned method to control the output voltage (V_CH) of the LED string or the driving voltage (V_LED) of the LED string.

[0069] FIG. 7 is a first example configuration diagram of an LED driving circuit according to the present embodiment.

[0070] Referring to FIG. 7, the display device (200) may include a microcontroller unit (250), an LED driving circuit (260), an LED string (270), a boost converter (290), etc.

[0071] The LED driving circuit (260) may include a headroom detection circuit (261), a channel control circuit (263), a digital logic circuit (263), a feedback transistor (264), etc.

[0072] The headroom detection circuit (261) can detect and monitor the output voltage (V_CH) of the LED string formed at one end of the LED string (270). The LED string (270) can be defined as a set including one or more LEDs, and the output voltage (V_CH) of the LED string is formed at the bottom of the LED string (270), the driving voltage (V_LED) of the LED string is formed at the top, and an LED current (I_LED) can flow through the LED.

[0073] The headroom detection circuit (261) can monitor whether the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF), and can transmit the magnitude value of the detected output voltage (V_CH) of the LED string or the deviation value of the difference between the reference voltage (V_REF) and the output voltage (V_CH) of the LED string to a microcontroller (250), etc.

[0074] The headroom detection circuit (261) can control the output voltage (V_CH) of the LED string to change—for example, increase the voltage—by controlling the digital logic circuit (263) to transmit the channel enable signal (CH_EN) to the channel control circuit (262) when the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF).

[0075] The headroom sensing circuit (261) can transmit the output voltage (V_CH) of the LED string to one terminal of the feedback transistor (264)—e.g., the gate terminal. The feedback transistor (264) can transmit information regarding the output voltage (V_CH) of the LED string measured by the headroom sensing circuit (261) to the microcontroller unit (250) while electrically isolating the LED driving circuit (260) and the microcontroller unit (250).

[0076] The channel control circuit (263) may be a circuit including a current source or a set of one or more transistors. The channel control circuit (263) may adjust the magnitude and timing of the output voltage (V_CH) of the LED string formed at the channel terminal, or adjust the magnitude and timing of the LED current (I_LED).

[0077] The channel control circuit (253) can control the magnitude of the output voltage (V_CH) or LED current (I_LED) of the LED string in response to the timing of the channel enable signal (CH_EN) generated and transmitted by the digital logic circuit (263). For example, when the channel enable signal (CH_EN) is in a high state, the output voltage (V_CH) of the LED string formed in the channel can be increased, and when the channel enable signal (CH_EN) is in a low state, the output voltage (V_CH) of the LED string formed in the channel can be decreased. In this case, the timing of the voltage increase and decrease may be the same, but there may be a certain time delay or deviation.

[0078] The channel control circuit (253) may include a switch circuit as shown in FIGS. 4 and 5. The channel control circuit (253) may include a first switch circuit that controls the state of the output voltage (V_CH) and the magnitude of the LED current (I_LED) of the light-emitting diode according to the duty ratio of the PWM (Pulse Width Modulation) operation control signal generated by the digital logic circuit (263). Additionally, the channel control circuit (253) may include a second switch circuit that receives the PAM (Pulse Amplitude Modulation) operation control signal generated by the digital logic circuit (263) and controls the state of the output voltage (V_CH) and the magnitude of the LED current (I_LED).

[0079] The digital logic circuit (263) can generate and transmit a channel enable signal (CH_EN) of the LED string to control the output voltage (V_CH) of the LED string. The digital logic circuit (263) can control the output voltage (V_CH) of one end of the LED string (270), but can also control the driving voltage (V_LED) of the LED string at the other end of the LED string (270).

[0080] The digital logic circuit can control the operation of the channel control circuit to increase the output voltage (V_CH) of the LED string by transmitting a high-state channel enable signal (CH_EN) to the channel control circuit when the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF), and to decrease the output voltage (V_CH) of the LED string by transmitting a low-state channel enable signal (CH_EN) to the channel control circuit when the output voltage (V_CH) of the LED string exceeds the preset reference voltage (V_REF). The output voltage (V_CH) of the LED string may be the same as the timing of the high and low states of the channel enable signal (CH_EN), but the increase and decrease may occur with a certain time delay.

[0081] Additionally, the digital logic circuit can control the operation of the channel control circuit to increase the driving current (I_LED) of the LED string by transmitting a high-state channel enable signal (CH_EN) to the channel control circuit when the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF), and to decrease the driving current (I_LED) of the LED string by transmitting a low-state channel enable signal (CH_EN) to the channel control circuit when the output voltage (V_CH) of the LED string exceeds the preset reference voltage (V_REF). The driving current (I_LED) of the LED string may be the same as the timing of the high and low states of the channel enable signal (CH_EN), but may increase and decrease with a certain time delay.

[0082] The output voltage (V_CH) of the LED string or the driving current (I_LED) of the LED string can be defined as corresponding to the timing of the channel enable signal (CH_EN).

[0083] The digital logic circuit (263) can count the number of clocks of the vertical synchronization signal (VSYNC) transmitted from outside the LED driving circuit (260) or count the number of clocks of the PWM clock signal generated by the internal oscillator.

[0084] For example, the digital logic circuit (263) can count the number of clocks transmitted during a certain time interval or measure the time taken to count a preset number of clocks. The digital logic circuit (263) can generate a control signal to adjust the output voltage (V_CH) of the LED string until a standard corresponding to a preset operating condition is satisfied, or generate a feedback signal to adjust the driving voltage (V_LED) of the LED string.

[0085] The feedback transistor (T3) (264) receives the voltage value of the output voltage (V_CH) of the LED string delivered to the gate terminal or the deviation value between the reference voltage (V_REF) and the output voltage (V_CH) of the LED string, and can change the current intensity based on the voltage formed at other terminals—e.g., source terminal, drain terminal. For example, the feedback transistor (264) can allow current to flow only when the voltage value of the output voltage (V_CH) of the LED string is less than or equal to the voltage value of the reference voltage (V_REF), and the intensity of the current flowing through the feedback transistor (264) can increase as the deviation increases.

[0086] The microcontroller unit (250) can receive voltage information formed at the first terminal—e.g., source or drain terminal—or the second terminal—e.g., drain or source terminal—of the feedback transistor (264) or current information flowing through the feedback transistor (264) to determine whether to adjust the driving voltage (V_LED) of the LED string (270). For example, the microcontroller unit (250) is electrically connected to the feedback transistor (264), measures the terminal current flowing through one terminal of the feedback transistor (264), and can generate a feedback control signal to adjust the magnitude of the driving voltage (V_LED) of the LED string.

[0087] The microcontroller unit (250) may further include a feedback control circuit (251), a digital-to-analog converter (252), etc. The feedback control circuit (251) can obtain information regarding the terminal current or terminal voltage of the feedback transistor (251), and can generate a feedback control signal and whether to provide feedback for the driving voltage (V_LED) of the LED string.

[0088] The microcontroller unit (250) obtains information regarding the rise or fall of the output voltage (V_CH) of the LED string through the current value flowing through one terminal of the feedback transistor (264)—for example, a terminal connected to the feedback port of the communication chip—and generates a feedback control signal to adjust the magnitude of the driving voltage (V_LED) of the LED string when the output voltage (V_CH) of the LED string is below the reference voltage (V_REF), thereby being able to adjust the output voltage of the boost converter—for example, the LED voltage (V_LED).

[0089] The feedback control circuit (251) can appropriately control the voltage rise of the booster converter (290) by changing the booster voltage (V_B) formed by the digital-analog converter (252) by considering the driving voltage (VCC), the first resistor (R1), the second resistor (R2), and the third resistor (R3).

[0090] The feedback control signal may be a control signal for operating a digital-to-analog converter (252) or a control signal for operating a booster converter (290). The feedback control signal may include a control value for controlling the driving voltage (V_LED) of an LED string or a corresponding code value.

[0091] If the LED driving circuit (260) does not perform a feedback operation to change the driving voltage (V_LED) of the LED string by monitoring the output voltage (V_CH) of the LED string by the headroom detection circuit (261) and feeding it back, or if it simply controls the on / off of the channel control circuit (262), then it will not be able to properly control the display brightness change through the repeated rising and falling of the output voltage (V_CH) of the LED string, or through the flicker phenomenon.

[0092] FIG. 8 is a second example configuration diagram of an LED driving circuit according to the present embodiment.

[0093] Referring to FIG. 8, the display device (300) may include an LED driving circuit (360), an LED string (370), a boost converter (390), etc.

[0094] The LED driving circuit (360) may include a headroom detection circuit (361), a channel control circuit (not shown), a digital logic circuit (363), a feedback transistor (364), a feedback control circuit (365), a digital-to-analog converter (366), a multiplexer (367), an oscillator (368), a horizontal synchronization port (369), etc.

[0095] The headroom detection circuit (361) can detect an output voltage (V_CH) or LED current (I_LED) formed at one end of the LED string (370)—for example, a current channel port of an LED driver chip. Here, the bottom end of the LED string (370) or the point connected to the current channel (CH) can be defined as the headroom.

[0096] The headroom detection circuit (361) can repeatedly measure the output voltage (V_CH) or LED current (I_LED) of the LED string for a preset time and compare it with the reference voltage (V_REF). Here, the preset time can be changed by a microcontroller unit (not shown) or internal operation control.

[0097] The digital logic circuit (363) can transmit a feedback signal (CS_FB1) to a feedback transistor (364) without directly controlling the channel on / off through a channel control circuit (not shown).

[0098] The digital logic circuit (363) can determine the feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the headroom detection circuit (361) determines that the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF).

[0099] In this case, the feedback timing may be a timing for counting the number of clocks by a preset counting number in the digital logic circuit (363), or a timing for resetting and updating frame by frame.

[0100] The digital logic circuit (363) can count the rising edge or falling edge of the vertical synchronization signal (VSYNC) for each frame, or count the number of clocks of the PWM clock signal generated by the internal oscillator (368).

[0101] The digital logic circuit (363) may set the number of clocks to be counted based on an arbitrary fixed value, such as 16 or 32, but may adjust the number of clocks to be counted after each frame or after a set feedback timing has elapsed. For example, the digital logic circuit (363) may adjust the number of clocks to be counted in proportion to the absolute value of the difference between the reference voltage (V_REF) obtained from the headroom detection circuit (361) and the output voltage (V_CH) of the LED string, and may increase the voltage change amount of the boost converter (390) in proportion to the number of clocks to be counted, but is not limited thereto.

[0102] The feedback transistor (364) can receive the output signal (CS_FB1) of the digital logic circuit (363) at its gate terminal.

[0103] The feedback control circuit (365) is connected to the first terminal of the feedback transistor (364) and can determine whether to adjust the driving voltage (V_LED) of the LED string based on the current value or voltage value (V_FB) flowing through the first terminal.

[0104] The digital-to-analog converter (366) can adjust the output signal based on the driving voltage control signal of the LED string transmitted by the feedback control circuit (365). For example, the digital-to-analog converter (366) can receive different digital code values ​​from the feedback control circuit (365) that determine the output analog signal.

[0105] The boost converter (390) can adjust the magnitude of the driving voltage (V_LED) of the LED string according to the booster voltage (V_B) determined by the output signal of the digital-analog converter. The boost converter (390) may be a type of DC-DC converter.

[0106] The multiplexer (367) can receive a PWM clock signal generated by an oscillator (368) inside the LED driving circuit (360) or receive an external horizontal synchronization signal (VSYNC) transmitted from a horizontal synchronization port (369), select one signal, and output it to a digital logic circuit (363). Through this configuration, the LED driving circuit (360) can control the operation by transmitting a feedback signal (CS_FB1) by pull-down to internal circuits (364, 365, 366, 390), etc., by the operation of the digital logic circuit (363).

[0107] The digital logic circuit (363) can count the rising edge or falling edge of the vertical synchronization signal (VSYNC) for every frame or every preset frame.

[0108] Additionally, the digital logic circuit (363) can count the number of clocks of the PWM clock signal generated by the internal oscillator (368).

[0109] The digital logic circuit (363) can adjust the clock counting count based on the output voltage (V_CH) of the LED string of the headroom detection circuit (361). In this case, by internally adjusting the counting method of the digital logic circuit (363) through digital calculation without adjusting the output voltage of the LED string formed in the channel, the noise phenomenon occurring in the channel and the flicker phenomenon of the display device can be improved.

[0110] That is, the digital logic circuit (363) can generate a feedback signal (CS_FB1) using an internal counter, without generating a feedback signal through the output voltage (V_CH) or LED current (I_LED) of the LED string. The digital logic circuit (363) can transmit a signal to the feedback transistor (364) that feeds back the voltage rise of the driving voltage (V_LED) of the LED string during the clock counting period.

[0111] The feedback control circuit (365) can determine the operating time of the digital-to-analog converter based on the counting count of the digital logic circuit (363).

[0112] The boost converter (390) can increase the driving voltage (V_LED) of the LED string in stages in response to the time interval of the driving voltage control signal of the LED string generated by the feedback control circuit (365).

[0113] The configuration of each circuit described in FIG. 8 can be understood as being physically separated or functionally separated within a single integrated circuit. For example, the booster converter (390) may be a separate circuit configuration from the LED driving circuit (360), but may also be a circuit configuration integrated within the LED driving circuit (360).

[0114] FIG. 9 is a first example timing diagram of signals processed in an LED driving circuit according to the present embodiment.

[0115] Referring to FIG. 9, the timing showing the change over time of the horizontal synchronization signal (VSYNC), PWM clock signal (FPWM), output voltage of the LED string (V_CH), channel enabling signal (CH_EN), feedback signal (FB), LED control signal (input signal of DAC), and driving voltage of the LED string (V_LED) of the LED driving circuit (200) of FIG. 7 can be compared.

[0116] The output voltage (V_CH) of the LED string of the channel detected by the headroom detection circuit (261) can repeatedly rise and fall over time, and this can correspond to the timing of the channel enabling signal (CH_EN).

[0117] An LED control signal (input signal of the DAC) can be output in response to the timing of a feedback signal (FB) formed at one end of a feedback transistor, and accordingly, the driving voltage (V_LED) of the LED string can change.

[0118] FIG. 10 is a second example timing diagram of signals processed in an LED driving circuit according to the present embodiment.

[0119] Referring to FIG. 10, the timing showing the change over time of the horizontal synchronization signal (VSYNC), PWM clock signal (FPWM), output voltage (V_CH) of the LED string, feedback signal (CS_FB1), and driving voltage (V_LED) of the LED string of FIG. 8 can be compared.

[0120] The headroom detection circuit (361) monitors the output voltage (V_CH) of the LED string, and the digital logic circuit (363) can continuously maintain the low state of the feedback signal (CS_FB1) by counting the external horizontal synchronization signal (V_SYNC) or the internal PWM clock signal (FPWM). In this case, the feedback control circuit (365) can continuously transmit the driving voltage control signal of the LED string for voltage increase, and the boost converter (390) can continuously control the increase of the driving voltage (V_LED) of the LED string.

[0121] The digital logic circuit (363) can terminate counting according to the termination of counting or reset of the external horizontal synchronization signal (V_SYNC) or the internal PWM clock signal (FPWM), and change the low state of the feedback signal (CS_FB1) to a high state.

[0122] The digital logic circuit (363) can adjust the number of times the digital logic circuit (363) counts the clock during a set time based on the difference value between the reference voltage (V_REF) and the output voltage (V_CH) of the LED string or the difference value between the reference current (I_REF) and the LED current (I_LED), or perform a counting operation that varies according to the counting time that satisfies the reference counting number.

[0123] In this way, by monitoring the output voltage (V_CH) of the LED string and generating a feedback signal (CS_FB1) for a set period of time, noise that may affect adjacent channels can be reduced. PWM driving is implemented through a counting circuit using external or internal clock counting, and by driving at a high PWM frequency without being limited by the display frame rate, a flicker-free effect can be achieved.

[0124] FIG. 11 is a flowchart of an LED driving method according to the present embodiment.

[0125] Referring to FIG. 11, the LED driving method (600) may include the steps of monitoring the output voltage of the LED string (S601), performing clock counting (S602), generating a feedback control signal (S603), controlling the output signal of the digital-to-analog converter (S604), and changing the driving voltage of the LED string (S605).

[0126] The step of monitoring the output voltage of the LED string (S601) may be a step of monitoring the output voltage (V_CH) of the LED string and determining whether it is below a reference voltage (V_REF). This operation may be performed in a headroom detection circuit, etc., and may involve monitoring the LED current (I_LED), etc., in addition to the output voltage (V_CH) of the LED string.

[0127] The step of performing clock counting (S602) may be a step of determining feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the output voltage (V_CH) of the LED string is less than or equal to the reference voltage (V_REF). This operation may be performed in a digital logic circuit, and the waveform and pulse width of the signal transmitted to the feedback transistor may vary depending on the number of rising edges or falling edges of the vertical synchronization signal or PWM clock signal transmitted by the multiplexer.

[0128] In addition, the digital logic circuit performs a clock counting operation when the output voltage (V_CH) of the LED string is less than or equal to the reference voltage (V_REF), and can stop the clock counting operation when the output voltage (V_CH) of the LED string exceeds the reference voltage (V_REF).

[0129] An external vertical synchronization signal (VSYNC) or an internal PWM clock signal is transmitted to a multiplexer, and only one selected signal among the vertical synchronization signal and the PWM clock signal can be transmitted to a digital logic circuit.

[0130] The step of generating a feedback control signal (S603) may be a step of changing the code value transmitted to the digital-to-analog converter according to the number and timing of clocks obtained from the feedback transistor.

[0131] The step of controlling the output signal of the digital-to-analog converter (S604) may be a step of changing the output analog signal according to the feedback control signal. Accordingly, the booster voltage (V_B), etc. formed on the signal line connected to the booster converter, may be changed, and the driving voltage (V_LED) of the LED string may change.

[0132] The step of changing the driving voltage of the LED string (S605) may be a step in which the driving voltage (V_LED) of the LED string is boosted by a boost converter. The boost operation time of the boost converter may be determined according to a counting criterion that varies according to the state of the output voltage (V_CH) of the LED string.

[0133] If necessary, a circuit for voltage boosting other than a boost converter may be used.

[0134] Figure 11 described above is an example of an LED control method, and the order of some steps may be changed or omitted, and the target of the circuit performing the aforementioned operation may be defined differently.

Claims

Claim 1 An LED driving circuit comprising: a headroom sensing circuit for sensing the output voltage (V_CH) of an LED string; a digital logic circuit for generating a channel enable signal (CH_EN) of the LED string to control the output voltage (V_CH) of the LED string; a channel control circuit for controlling the magnitude of the output voltage (V_CH) of the LED string in response to the timing of the channel enable signal (CH_EN) of the digital logic circuit; and a feedback transistor for receiving the output voltage of the LED string detected by the headroom sensing circuit, wherein the feedback transistor is electrically connected to a microcontroller unit to control the driving voltage (V_LED) of the LED string, and the microcontroller unit measures the current flowing through the feedback transistor and generates a feedback control signal to control the magnitude of the driving voltage (V_LED) of the LED string to control the operation of a boost converter. Claim 2 In claim 1, the headroom detection circuit is an LED driving circuit that monitors whether the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF). Claim 3 In claim 2, the digital logic circuit controls the operation of the channel control circuit such that when the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF), it transmits a high-state channel enable signal (CH_EN) to the channel control circuit to raise the output voltage (V_CH) of the LED string, and when the output voltage (V_CH) of the LED string exceeds the preset reference voltage (V_REF), it transmits a low-state channel enable signal (CH_EN) to the channel control circuit to lower the output voltage (V_CH) of the LED string. Claim 4 In claim 1, the digital logic circuit counts the clock of a vertical synchronization signal (VSYNC) transmitted from the outside or counts the clock of a PWM clock signal generated by an internal oscillator, an LED driving circuit. Claim 5 In claim 1, the channel control circuit comprises: a first switch circuit that adjusts the magnitude of the output voltage (V_CH) of the LED string of the light-emitting diode according to the duty ratio of a PWM (Pulse Width Modulation) operation control signal generated by the digital logic circuit; and a second switch circuit that receives a PAM (Pulse Amplitude Modulation) operation control signal generated by the digital logic circuit and adjusts the magnitude of the output voltage (V_CH) of the LED string of the light-emitting diode. Claim 6 In claim 1, the microcontroller unit obtains information regarding the rise or fall of the output voltage (V_CH) of the LED string through the current value flowing through the feedback transistor, and when the output voltage (V_CH) of the LED string is less than or equal to the reference voltage (V_REF), generates the feedback control signal to adjust the magnitude of the driving voltage (V_LED) of the LED string and adjusts the output voltage of the boost converter. Claim 7 An LED driving circuit comprising: a headroom sensing circuit for detecting an output voltage (V_CH) of an LED string formed at one end of an LED string; a digital logic circuit for determining a feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the headroom sensing circuit determines that the output voltage (V_CH) of the LED string is below a preset reference voltage (V_REF); a feedback transistor for receiving an output signal of the digital logic circuit; and a feedback control circuit connected to a first terminal of the feedback transistor and determining whether to adjust the driving voltage (V_LED) of the LED string based on the current value flowing through the first terminal. Claim 8 In claim 7, the LED driving circuit further comprises: a digital-to-analog converter that adjusts an output signal based on a driving voltage control signal of an LED string transmitted by the feedback control circuit; and a boost converter that adjusts the magnitude of the driving voltage (V_LED) of the LED string according to the output signal of the digital-to-analog converter. Claim 9 In claim 7, the headroom sensing circuit is an LED driving circuit that repeatedly measures the output voltage (V_CH) of the LED string for a preset time and compares it with a reference voltage (V_REF). Claim 10 In claim 7, the digital logic circuit counts the rising edge or falling edge of the vertical synchronization signal (VSYNC) for every frame, or the digital logic circuit counts the number of clocks of the PWM clock signal generated by an internal oscillator, and the LED driving circuit adjusts the number of clock counts based on the output voltage (V_CH) of the LED string of the headroom sensing circuit. Claim 11 An LED driving circuit according to claim 7, further comprising a multiplexer that selects the external vertical synchronization signal (VSYNC) or the internal PWM clock signal and outputs it to the digital logic circuit. Claim 12 In claim 7, the digital logic circuit is an LED driving circuit that transmits a signal to the feedback transistor for feedbacking a voltage rise of the driving voltage (V_LED) of the LED string during the period of performing clock counting. Claim 13 In claim 8, the feedback control circuit determines the operating time of the digital-to-analog converter based on the counting count of the digital logic circuit, an LED driving circuit. Claim 14 In claim 8, the boost converter is an LED driving circuit that increases the driving voltage (V_LED) of the LED string in steps in response to the time interval of the driving voltage control signal of the LED string generated by the feedback control circuit. Claim 15 In claim 7, the LED driving circuit is an LED driving circuit that drives an LED in response to the timing of a vertical synchronization signal (VSYNC) transmitted from the outside or the timing of a PWM signal transmitted from the inside, regardless of the display frame rate. Claim 16 In claim 7, the LED driving circuit is an LED driving circuit that does not perform on / off control of the output voltage (V_CH) of the LED driving circuit. Claim 17 An LED driving method comprising: a step of monitoring the output voltage (V_CH) of an LED string and determining whether it is below a reference voltage (V_REF); a step of determining a feedback timing by counting the clock of an external vertical synchronization signal (VSYNC) or an internal PWM clock signal when the output voltage (V_CH) of the LED string is below the reference voltage (V_REF); and a step of adjusting the intensity of the driving voltage (V_LED) of the LED string during the feedback timing. Claim 18 In claim 17, the monitoring of the output voltage (V_CH) of the LED string is performed by a headroom sensing circuit disposed at one end of the LED string, and when the output voltage (V_CH) of the LED string is less than or equal to a reference voltage (V_REF), a clock counting operation of a digital logic circuit is performed. Claim 19 In claim 17, the external vertical synchronization signal (VSYNC) or the internal PWM clock signal is transmitted to a multiplexer, and only one selected signal among the vertical synchronization signal and the PWM clock signal is transmitted to a digital logic circuit, an LED driving method. Claim 20 In claim 17, the driving voltage (V_LED) of the LED string is boosted by a boost converter, and the boosting operation time of the boost converter is determined according to a counting criterion that varies according to the state of the output voltage (V_CH) of the LED string, an LED driving method.

Images