Step-down liquid crystal screen LED constant current drive circuit

Abstract

The utility model discloses a step-down liquid crystal screen LED constant-current drive circuit, which belongs to the technical field of metal hose performance testing, and comprises a step-down LED constant-current drive chip and an LED, when the step-down LED constant-current drive chip acts, voltage division is carried out by configuring different resistance values, so that different working modes are selected, and the LED constant-current drive chip is used for driving the LED to work. A capacitor is additionally arranged at the input end to guarantee the stability of an input power supply, the GND pin end of the step-down LED constant-current driving chip is connected with the Vin input end of the power supply through the capacitor, and the SEN current detection pin of the step-down LED constant-current driving chip is connected with the positive electrode of the LED. When the size of the LED backlight is lower than the actual power supply input voltage, the DC / DC power supply chip is firstly used for reducing the voltage, and then the LED is used for boosting the voltage, so that the material cost can be greatly saved; in addition, the step-down liquid crystal screen LED constant current driving circuit is lower in power consumption and higher in power supply conversion efficiency.

Description

Technical Field

[0001] This utility model relates to the field of driving circuit technology, and more specifically, to a step-down LED constant current driving circuit for LCD screens. Background Technology

[0002] The display principle of an LCD screen mainly consists of an LED backlight driver circuit, a TCON circuit, and a signal control circuit. Among these, LED backlight is a prerequisite for the LCD screen to light up. Only by designing a good LED backlight driver circuit can the LCD screen meet the required brightness and power consumption requirements.

[0003] Currently, the LED backlight driver circuits we use are often boost-type circuits, such as a power input of DC24V. However, the LED backlight voltage of LCD screens usually far exceeds DC24V, such as DC36V, DC48V, or even higher. Therefore, conventional LCD screen backlight LED driver circuits are boost-type circuits to meet the usage requirements.

[0004] However, with the diversification of our products, the size and power consumption requirements of the LCD screen have become particularly important. When the LCD screen size is small and the power consumption and voltage of the LED backlight are relatively low, using a boost-type LED backlight driver circuit is not the optimal choice. For example, when the external input voltage is DC24V and the LCD screen LEDs require DC10V power, the conventional approach is to use a DC / DC power supply chip to convert the external DC24V voltage to approximately DC5V, and then use a boost-type LED backlight driver chip to convert the DC5V to the 10V required by the LEDs. This not only wastes a DC / DC power supply chip, increasing costs, but also reduces the efficiency of the power supply, as DC / DC converters themselves only have a conversion efficiency of 80%-90%. Therefore, this solution proposes a buck-type LCD screen LED constant current driver circuit. Utility Model Content

[0005] 1. Technical problem to be solved:

[0006] To address the problems existing in the prior art, the purpose of this utility model is to provide a step-down LED constant current drive circuit for LCD screens. This circuit solves the problem in existing LED boost constant current drives where the LED backlight size is lower than the actual power input voltage. This process involves first using a DC / DC power chip to step down the voltage and then using the LED to boost it, which can greatly save on material costs. Furthermore, the step-down LED constant current drive circuit for LCD screens has lower power consumption and higher power conversion efficiency, thereby effectively solving the problem of limited power input capability of the circuit.

[0007] 2. Technical Solution:

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] A step-down LED constant current driving circuit for a liquid crystal display includes a step-down LED constant current driving chip and an LED light-emitting diode. The step-down LED constant current driving chip performs voltage division by configuring different resistance values, thereby selecting different operating modes. A capacitor is added to the input terminal to ensure the stability of the input power supply. The GND pin of the step-down LED constant current driving chip is connected to the Vin input terminal of the power supply through a capacitor. The SEN current detection pin of the step-down LED constant current driving chip is connected to the positive terminal of the LED light-emitting diode.

[0010] A further improvement is that a Cin10μf capacitor is connected in parallel between the GND pin and the Vin input pin of the step-down LED constant current driver chip.

[0011] A further improvement is that a set of REN resistors is connected in parallel between the GND pin and the Vin input of the buck LED constant current driver chip. The set of REN resistors includes two resistors, REN1 and REN2. The REN1 and REN2 resistors are connected in series and then in parallel between the GND pin and the Vin input. One end of the REN1 resistor is connected to the EN pin of the buck LED constant current driver chip.

[0012] A further improvement is that a Cf10nF capacitor is connected to ground at the CF pin of the step-down LED constant current driver chip.

[0013] A further improvement is that the IN pin of the step-down LED constant current driver chip is the positive input terminal of the current detection pin, and an Rsen current-limiting resistor is connected in parallel between the IN pin and the negative input terminal of the SEN current detection pin.

[0014] A further improvement is that a Cout capacitor is connected in parallel between the positive and negative terminals of the LED.

[0015] A further improvement is that: one end of the LX pin of the step-down LED constant current driver chip is connected to the negative terminal of the LED light-emitting diode, and the other end is connected to the circuit of the Vin input terminal through a diode.

[0016] The input voltage VIN is DC 24V. After passing through the XC8612 step-down LED constant current driver chip, the LED+ and LED- at the back end are connected to the LED+ and LED- of the LCD screen respectively to drive the LED backlight. Capacitors can be added to the front and back ends to control the backlight temperature and prevent backlight flickering. The peripheral circuit is simple, and the current is adjusted via RSEN, making it easy to operate.

[0017] 3. Beneficial effects:

[0018] Compared with the prior art, the technical solution provided by this utility model has the following advantages:

[0019] (1) Low cost: It can save the traditional process of first stepping down the voltage with a DC / DC power chip and then stepping up the voltage, thus reducing the cost of use for enterprises;

[0020] (2) Low power consumption and high power efficiency: The step-down LCD screen LED only requires one step-down chip and a small number of external resistors and capacitors, generating less heat during use, which is more in line with energy conservation and emission reduction;

[0021] (3) It has two dimming modes: analog dimming and PWM dimming;

[0022] (4) Simple design: meets the needs of miniaturized or low-voltage LED screens.

[0023] It should be noted that the structures not described in this utility model are the same as or can be implemented using existing technology, and will not be elaborated here, as they do not involve the design points and improvement directions of this utility model. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the LED constant current drive circuit for the step-down LCD screen of this utility model;

[0025] Figure 2 This is a schematic diagram illustrating the principle of adjusting LED brightness by adjusting the duty cycle.

[0026] Figure 3 This is a schematic diagram illustrating the principle of adjusting the LED brightness by adjusting the voltage of the CF circuit.

[0027] Figure 4 This is the layout diagram of the step-down LCD screen LED constant current drive circuit of this utility model. Detailed Implementation

[0028] To facilitate understanding of this utility model, a more comprehensive description of the utility model will be given below with reference to the accompanying drawings, which show several embodiments of the utility model. However, the utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the utility model will be more thorough and complete.

[0029] Please see Figure 1-4A step-down LED constant current driving circuit for a liquid crystal display includes a step-down LED constant current driving chip and an LED light-emitting diode. The step-down LED constant current driving chip performs voltage division by configuring different resistance values, thereby selecting different operating modes. A capacitor is added to the input terminal to ensure the stability of the input power supply. The GND pin of the step-down LED constant current driving chip is connected to the Vin input terminal of the power supply through a capacitor. The SEN current detection pin of the step-down LED constant current driving chip is connected to the positive terminal of the LED light-emitting diode.

[0030] In this solution, a buck-type LED constant current drive circuit for LCD screens solves the problem of using a DC / DC power chip to step down the voltage and then using the LED to boost the voltage when the backlight size of the LED is lower than the actual power input voltage in traditional LED boost constant current drive, which can greatly save material costs. On the other hand, the buck-type LED constant current drive circuit for LCD screens has lower power consumption and higher power conversion efficiency, thus effectively solving the problem of limited power input capability of the circuit.

[0031] In this embodiment, the buck LED constant current driver chip is model XC8612. It is an LED driver chip with an input voltage range of 12V to 60V, which integrates a low-impedance MOSFET and a compensation circuit, resulting in a very simplified peripheral circuit. The chip also supports analog dimming and PWM dimming functions, with a smooth dimming curve; it supports a switching frequency of 500kHz, and the maximum output current can reach over 2A.

[0032] More specifically, a Cin10μf capacitor is connected in parallel between the GND pin and the Vin input pin of the buck LED constant current driver chip.

[0033] More specifically: A set of REN resistors is connected in parallel between the GND pin and the Vin input of the buck LED constant current driver chip. The set of REN resistors includes two resistors, REN1 and REN2. The REN1 and REN2 resistors are connected in series and then in parallel between the GND pin and the Vin input. One end of the REN1 resistor is connected to the EN pin of the buck LED constant current driver chip.

[0034] More specifically, the CF pin of the step-down LED constant current driver chip is connected to ground via a Cf10nF capacitor.

[0035] More specifically: the IN pin of the step-down LED constant current driver chip is the positive input terminal of the current detection pin, and an Rsen current-limiting resistor is connected in parallel between it and the negative input terminal of the SEN current detection pin.

[0036] More specifically, a Cout capacitor is connected in parallel between the positive and negative terminals of the LED.

[0037] More specifically: one end of the LX pin of the step-down LED constant current driver chip is connected to the negative terminal of the LED light-emitting diode through a 22UH inductor, and the other end is connected to the Vin input circuit through a diode.

[0038] In this solution, the input voltage is DC24V and the current at the VIN terminal is passed through the XC8612 step-down LED constant current driver chip. The LED+ and LED- at the back end are connected to the LED+ and LED- of the LCD screen respectively to drive the LED backlight. Capacitors can be added to the front and back ends to heat the backlight and prevent backlight jitter. The current can be adjusted in the external circuit through RSEN, which is easy to operate.

[0039] In this embodiment, the dimming mode is divided into analog dimming and PWM dimming. When the voltage of the CF pin is greater than 1.6V, it enters the PWM dimming mode. At this time, CF can be connected to 3.3V, and the EN pin can be connected to the timer pin of a common microcontroller. The brightness of the LED can be adjusted by adjusting the duty cycle.

[0040] When the voltage at the EN pin is greater than 8.5V, it enters the analog dimming mode. In analog dimming, the brightness of the LED can be adjusted by adjusting the voltage of the CF pin (above 1.6V).

[0041] In this embodiment, the names of the corresponding circuits are represented as follows:

[0042] REN stands for "Control Data Receive Bits";

[0043] GND stands for "grounding terminal of the wire";

[0044] EN foot indicates "enabling foot";

[0045] LX stands for "external inductor";

[0046] Rsen stands for "current limiting resistor".

[0047] The specific installation steps are as follows: The input terminal Vin is the input voltage of the power supply, with an input range of 12V to 60V DC voltage. A Cin capacitor is connected in parallel between the Vin input terminal and the GND pin of the XC8612 chip for filtering. Usually, a capacitor of 10μF or higher is selected to ensure the stability of the input power supply. Resistors REN1 and REN2 are connected in series and then in parallel between the input and GND. One end of REN1 is connected to the EN pin of the chip. By configuring different resistor values, voltage division is performed to adjust the voltage of the EN pin for analog dimming or PWM dimming. When performing analog dimming, a Cf10nF capacitor is added to the CF pin to ensure the stability of analog dimming.

[0048] The output chip LX is connected to an inductor. One end uses a 22uH inductor connected to LED-, and the other end uses a diode connected to Vin to prevent backflow and chip damage. IN is the positive input of the current sensing pin, and an Rsen current-limiting resistor is connected in parallel between IN and the negative input of the SEN current sensing pin. The LED output current can be calculated by 0.1 / Rsen. A Cout capacitor, usually >10uF, can be connected in parallel to the output LED- and LED+ pins to filter the output voltage. The LEDs shown in the figure are the backlight strips that actually require power, and they can be connected in parallel to the chip output pins LED+ and LED-.

[0049] The above-described embodiments are merely illustrative of certain implementations of this utility model, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of this utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these modifications and improvements all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A step-down LED constant current driving circuit for a liquid crystal display screen, comprising a step-down LED constant current driving chip and an LED light-emitting diode, wherein the step-down LED constant current driving chip functions to perform voltage division by configuring different resistance values, thereby selecting different operating modes, characterized in that: The GND pin of the buck LED constant current driver chip is electrically connected to the Vin input of the power supply, and the SEN current detection pin of the buck LED constant current driver chip is connected to the positive terminal of the LED light-emitting diode.

2. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: A 10μF capacitor (Cin) is connected in parallel between the GND pin and the Vin input pin of the buck LED constant current driver chip.

3. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: A set of REN resistors is also connected in parallel between the GND pin and the Vin input of the buck LED constant current driver chip. The set of REN resistors includes two resistors, REN1 and REN2. The REN1 and REN2 resistors are connected in series and then in parallel between the GND pin and the Vin input. One end of the REN1 resistor is connected to the EN pin of the buck LED constant current driver chip.

4. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: The CF pin of the step-down LED constant current driver chip is connected to ground via a Cf10nF capacitor.

5. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: The IN pin of the step-down LED constant current driver chip is the positive input terminal of the current detection pin, and an Rsen current-limiting resistor is connected in parallel between it and the negative input terminal of the SEN current detection pin.

6. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: A Cout capacitor is connected in parallel between the positive and negative terminals of the LED.

7. The step-down LED constant current driving circuit for a liquid crystal display screen according to claim 1, characterized in that: One end of the LX pin of the step-down LED constant current driver chip is connected to the negative terminal of the LED light-emitting diode through a 22UH inductor, and the other end is connected to the Vin input circuit through a diode.

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