LED backlight driving circuit and pre-charge circuit thereof

Abstract

The application discloses an LED backlight drive chip, which comprises an LED pin, a high-voltage MOS switch tube M1, a low-voltage drive current MOS switch tube M2, an operational amplifier, a drive resistor and a pre-charge module; the pre-charge module comprises a pre-charge MOS switch tube M3, a pre-charge power supply and a pre-charge control unit. The LED backlight drive chip utilizes the body diode characteristics of the high-voltage MOS tube, sets the control MOS tube in the pre-charge circuit as a low-voltage device, thereby reducing the layout area of the semiconductor integrated circuit. And the fast response characteristics of the low-voltage MOS device are utilized to improve the pre-charge efficiency.

Description

Technical Field

[0001] This invention relates to the field of LED backlight technology, and in particular to an LED backlight driving circuit and its pre-charging circuit. Background Technology

[0002] Liquid crystal displays (LCDs) are the most prevalent type of display panel in modern applications. The liquid crystal material used in LCD panels is not self-emissive and requires a backlight to provide illumination. LED backlights, with their advantages of energy saving, environmental friendliness, and high performance, are widely used in LCD display panels. The performance of the LED backlight driver chip is crucial to the LCD display panel's performance.

[0003] like Figure 1-2 The diagram shown illustrates the existing LED backlight driving circuit and pre-charging circuit structure. A traditional matrix scanning LED backlight driving circuit structure is shown below. Figure 1 The current source at the low potential end is continuously reused by the switch HS_SW at the high potential end. When the cathode voltage of the LED string is relatively low and the PWM control terminal of the high-voltage MOS switch M1 is 0 at the same time, once the high-side switch HS_SW switches, it can cause the corresponding LED string to be affected by the parasitic capacitance C. p The LED flickers under the influence of the switch, and the LED cathode needs to be pre-charged with voltage during the dead time of the switch switching.

[0004] Pre-charge circuits in the prior art, such as Figure 2 When PWM = 0, the high-voltage MOS switch M1 is turned off, and the pre-charge MOS switch M3 is turned on. The drive voltage provided by the pre-charge power supply will flow through the pre-charge MOS switch M3 to the parasitic capacitance C of the LED pin. p The pre-charge circuit is designed to ensure that the LED pin voltage remains at the required system voltage when PWM=0. Since the LED pins need to withstand high voltage operation (e.g., the cathode voltage of an LED string reaches 40V when forward-biased), M3 also requires a high-voltage switching transistor. To ensure the LED port can be charged quickly, the on-resistance of the pre-charge MOS switch M3 needs to be relatively small, and the driving capability of the pre-charge control unit needs to be relatively strong to guarantee a rapid charging of the LED port voltage. These performance requirements for the pre-charge circuit result in the need for a relatively large chip area and high power consumption in existing technologies. Furthermore, in integrated circuit design, large semiconductor layouts and the use of high-voltage devices significantly increase chip manufacturing costs.

[0005] Therefore, there is a need in the existing technology for an LED backlight driving circuit and pre-charging circuit with lower chip manufacturing costs. Summary of the Invention

[0006] This invention proposes an LED backlight driving circuit. This circuit utilizes the body diode characteristics of a high-voltage MOSFET to configure the control MOSFET in the pre-charge circuit as a low-voltage device, thereby reducing the layout area of ​​the semiconductor integrated circuit. Furthermore, the fast response characteristics of the low-voltage MOSFET improve the pre-charge efficiency.

[0007] Based on the above technical objectives, the present invention provides an LED backlight driving circuit, the LED backlight driving circuit comprising: LED pins, a high-voltage MOS switch M1, a low-voltage drive current MOS switch M2, an operational amplifier, a drive resistor, and a pre-charge module; the pre-charge module comprises a pre-charge MOS switch M3, a pre-charge power supply, and a pre-charge control unit.

[0008] The LED pin is used to connect to the cathode of the LED string. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2.

[0009] The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is grounded. The inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2.

[0010] The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit.

[0011] In one embodiment, the high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are NMOS switches.

[0012] In one embodiment, the pre-charge MOS switch M3 is an NMOS switch.

[0013] In one embodiment, when the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on, and the pre-charge power supply at the drain terminal of the pre-charge MOS switch M3 applies a voltage to the source terminal of the high-voltage MOS switch M1.

[0014] In one embodiment, the parasitic capacitance C on the LED pinp The charging speed is controlled by the voltage provided by the pre-charging power supply.

[0015] The present invention also provides another LED backlight driving circuit, the LED backlight driving circuit comprising: LED pins, high voltage MOS switch M1, low voltage drive current MOS switch M2, operational amplifier, drive resistor and pre-charge module; the pre-charge module comprises pre-charge MOS switch M3, pre-charge power supply and pre-charge control unit;

[0016] The LED pin is used to connect to the cathode of the LED string. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2.

[0017] The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is connected to an external drive power supply. The inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2.

[0018] The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit.

[0019] In one embodiment, the high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are PMOS switches.

[0020] In one embodiment, the pre-charge MOS switch M3 is a PMOS switch.

[0021] In one embodiment, when the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on, and the pre-charge power supply at the drain terminal of the pre-charge MOS switch M3 applies a voltage to the source terminal of the high-voltage MOS switch M1.

[0022] Compared with the prior art, one or more embodiments of the present invention may have the following advantages:

[0023] The LED backlight driver of this invention utilizes the body diode characteristics of a high-voltage MOSFET to set the control MOSFET in the pre-charge circuit as a low-voltage device, thereby reducing the layout area of ​​the semiconductor integrated circuit. Furthermore, the fast response characteristics of the low-voltage MOSFET improve the pre-charge efficiency.

[0024] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 This is a schematic diagram of a matrix LED backlight driving circuit in the prior art;

[0027] Figure 2 This is a schematic diagram of a pre-charging circuit structure in the prior art;

[0028] Figure 3 This is a schematic diagram of the LED backlight driving circuit structure according to the first embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the LED backlight driving circuit structure according to the second embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this invention, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And when a second element, component, area, layer, or portion is discussed, it does not imply that the first element, component, area, layer, or portion necessarily exists in this invention.

[0032] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0034] Example 1

[0035] like Figure 3As shown, the LED backlight driving circuit of the present invention includes: LED pins, high-voltage MOS switch M1, low-voltage drive current MOS switch M2, operational amplifier, drive resistor, and pre-charge module; the pre-charge module includes pre-charge MOS switch M3, pre-charge power supply, and pre-charge control unit.

[0036] The LED pin is used to connect to the cathode of the LED string. The high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are NMOS switches. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal, that is, the PWM signal controls the conduction or cutoff of the high-voltage MOS switch M1. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2.

[0037] The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is grounded. The inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2. The external reference voltage V... ref The driving current of the LED string is determined by the driving resistor.

[0038] The pre-charge MOS switch M3 is an NMOS switch. The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit. In this embodiment, when the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on. Then, the pre-charge power supply at the drain of the pre-charge MOS switch M3 applies a voltage to the source of the high-voltage MOS switch M1. Since the high-voltage MOS switch M1 has an equivalent body diode between its source and drain when it is in the off state, when the pre-charge power supply provides a certain voltage value, this can achieve source-to-drain conduction of the high-voltage MOS switch M1, thereby charging the parasitic capacitance Cp on the LED pin. Furthermore, the charging speed can be controlled by the voltage provided by the pre-charge power supply.

[0039] On the other hand, since the source of the pre-charge MOS switch M3 in this embodiment is connected to the source of the high-voltage MOS switch M1, the source voltage of the pre-charge MOS switch M3 is in the low-voltage range. Therefore, the pre-charge MOS switch M3 does not need to use a high-voltage device, which saves a lot of chip area in integrated circuit design. Furthermore, as a low-voltage device, the pre-charge MOS switch M3 has a faster response speed than the high-voltage charging MOS transistors in the prior art, enabling it to complete the charging operation of parasitic capacitance within a short time interval.

[0040] Example 2

[0041] like Figure 4 As shown, the LED backlight driving circuit of the present invention includes: LED pins, a high-voltage MOS switch M1, a low-voltage drive current MOS switch M2, an operational amplifier, a drive resistor, and a pre-charge module; the pre-charge module includes a pre-charge MOS switch M3, a pre-charge power supply, and a pre-charge control unit.

[0042] The LED pin is used to connect to the anode of the LED string. The high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are PMOS switches. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal, that is, the PWM signal controls the conduction or cutoff of the high-voltage MOS switch M1. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2.

[0043] The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is connected to an external drive power supply. The external drive power supply is a negative voltage power supply. The inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2. The external reference voltage V... ref The driving current of the LED string is determined by the driving resistor.

[0044] The pre-charge MOS switch M3 is a PMOS switch. The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit. In this embodiment, when the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on. Then, the pre-charge power supply at the drain of the pre-charge MOS switch M3 applies a voltage to the source of the high-voltage MOS switch M1. Since the high-voltage MOS switch M1 has an equivalent body diode between its source and drain when it is in the off state, when the pre-charge power supply provides a certain voltage value, this can achieve source-to-drain conduction of the high-voltage MOS switch M1, thereby charging the parasitic capacitance Cp on the LED pin. Furthermore, the charging speed can be controlled by the voltage provided by the pre-charge power supply.

[0045] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An LED backlight drive circuit, characterized by, The LED backlight driving circuit includes: LED pins, high-voltage MOS switch M1, low-voltage drive current MOS switch M2, operational amplifier, drive resistor, and pre-charge module; the pre-charge module includes pre-charge MOS switch M3, pre-charge power supply, and pre-charge control unit. The LED pin is used to connect to the cathode of the LED string. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2. The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is grounded; the inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2. The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit.

2. The LED backlight drive circuit of claim 1, wherein, The high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are NMOS switches.

3. The LED backlight drive circuit of claim 1, wherein, The pre-charge MOS switch M3 is an NMOS switch.

4. The LED backlight drive circuit of claim 1, wherein, When the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on, and the pre-charge power supply at the drain terminal of the pre-charge MOS switch M3 applies a voltage to the source terminal of the high-voltage MOS switch M1.

5. The LED backlight drive circuit of claim 1, wherein, The parasitic capacitance C on the LED pin p The charging speed at which the LED is charged is controlled by the voltage provided by the pre-charge power supply.

6. An LED backlight drive circuit, characterized by, The LED backlight driving circuit includes: LED pins, high-voltage MOS switch M1, low-voltage drive current MOS switch M2, operational amplifier, drive resistor, and pre-charge module; the pre-charge module includes pre-charge MOS switch M3, pre-charge power supply, and pre-charge control unit. The LED pin is used to connect to the cathode of the LED string. The drain of the high-voltage MOS switch M1 is connected to the LED pin. The gate of the high-voltage MOS switch M1 is controlled by a PWM signal. The source of the high-voltage MOS switch M1 is connected to the drain of the low-voltage drive current MOS switch M2. The gate of the low-voltage drive current MOS switch M2 is connected to the output terminal of the operational amplifier, and the non-inverting input terminal of the operational amplifier receives an external reference voltage V. ref The source of the low-voltage drive current MOS switch M2 is connected to one end of the drive resistor, and the other end of the drive resistor is connected to an external drive power supply; the inverting input of the operational amplifier is connected to the source of the low-voltage drive current MOS switch M2. The source of the pre-charge MOS switch M3 is connected to the source of the high-voltage MOS switch M1, the drain of the pre-charge MOS switch M3 is connected to the pre-charge power supply, and the gate of the pre-charge MOS switch M3 is connected to the pre-charge control unit.

7. The LED backlight drive circuit of claim 6, wherein, The high-voltage MOS switch M1 and the low-voltage drive current MOS switch M2 are PMOS switches.

8. The LED backlight drive circuit of claim 6, wherein, The pre-charge MOS switch M3 is a PMOS switch.

9. The LED backlight drive circuit of claim 6, wherein, When the PWM signal controlling the gate of the high-voltage MOS switch M1 is low, the pre-charge control unit controls the pre-charge MOS switch M3 to turn on, and the pre-charge power supply at the drain terminal of the pre-charge MOS switch M3 applies a voltage to the source terminal of the high-voltage MOS switch M1.

10. An LED backlight panel, wherein the LED backlight panel uses an LED backlight driving circuit as described in any one of claims 1-9 to drive LED light-emitting elements to emit light.

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