Overcurrent protection circuit for LCD backlight module

Abstract

This application relates to an overcurrent protection circuit for an LCD backlight module, comprising: an input terminal, a control module, a sampling module, and a load module. The control module is electrically connected to the input terminal. The sampling module includes a MOSFET QT1, resistors RV1 and R2, a capacitor C1, and a diode DT1. The gate of MOSFET QT1 is electrically connected to the control module, the source of MOSFET QT1 is electrically connected to the first terminal of resistor RV1, the second terminal of resistor RV1 is grounded, the first terminal of resistor R2 is electrically connected to the control module, the second terminal of resistor R2 is electrically connected to the first terminal of diode DT1 and the first terminal of capacitor C1, the second terminal of diode DT1 is electrically connected to the first terminal of resistor RV1, and the second terminal of capacitor C1 is electrically connected to the drain of MOSFET QT1. The load module is electrically connected to the input terminal and the drain of MOSFET QT1. This application can prevent the compensation current from causing overload to the backlight module.

Description

Technical Field

[0001] This invention relates to the field of LCD backlight module circuit technology, and in particular to an overcurrent protection circuit for an LCD backlight module. Background Technology

[0002] In related technologies, the poor heat dissipation of LCD backlight modules leads to a sharp increase in LED junction temperature, causing overheating. As the operating temperature rises, luminous efficacy decreases, and the chip circuit automatically compensates for this by increasing the output current, creating a positive feedback loop of thermal runaway. However, when the backlight module carries a large current, it can cause overcurrent breakdown and burnout of the LED chips. Furthermore, the generated Joule heat can melt the solder or copper foil circuitry of the LED chips on the LED strip, resulting in an open circuit in the LED strip and causing uneven brightness distribution in the backlight module. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide an overcurrent protection circuit for an LCD backlight module, which can prevent the compensation current from causing overload to the backlight module and avoid burning out the backlight module.

[0004] The objective of this invention is achieved through the following technical solution: This application provides an overcurrent protection circuit for an LCD backlight module, comprising: an input terminal; a control module electrically connected to the input terminal; a sampling module including a MOSFET QT1, a resistor RV1, a resistor R2, a capacitor C1, and a diode DT1, wherein the gate of the MOSFET QT1 is electrically connected to the control module, the source of the MOSFET QT1 is electrically connected to a first terminal of the resistor RV1, the second terminal of the resistor RV1 is grounded, the first terminal of the resistor R2 is electrically connected to the control module, the second terminal of the resistor R2 is electrically connected to both the first terminal of the diode DT1 and the first terminal of the capacitor C1, the second terminal of the diode DT1 is electrically connected to the first terminal of the resistor RV1, and the second terminal of the capacitor C1 is electrically connected to the drain of the MOSFET QT1; and a load module electrically connected to both the input terminal and the drain of the MOSFET QT1.

[0005] The control module includes a resistor R1, with its first end electrically connected to the input terminal and its second end electrically connected to the gate of the MOS transistor QT1.

[0006] The control module also includes a transistor QT2, the collector of which is electrically connected to the second end of the resistor R1, the base of which is electrically connected to the first end of the resistor R2, and the emitter of which is grounded.

[0007] The load module includes several LED groups, with the first end of each LED group electrically connected to the input terminal and the second end of each LED group electrically connected to the drain of the MOSFET QT1.

[0008] Compared with the prior art, the present invention has at least the following advantages: While the LED chip monitors brightness decay and continuously injects drive current, the MOSFET QT1 constantly switches on and off, playing an overcurrent protection role. This prevents the backlight load from burning out due to current overload and also avoids overcurrent breakdown of the LED chip. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0010] Figure 1 This is a functional block diagram of the overcurrent protection circuit of the LCD backlight module in one embodiment of the present invention; Figure 2 This is a circuit diagram of an overcurrent protection circuit for an LCD backlight module according to an embodiment of the present invention. Detailed Implementation

[0011] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0012] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0013] Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0014] The poor heat dissipation of LCD backlight modules leads to a rapid increase in LED junction temperature, causing overheating. As the operating temperature rises, luminous efficacy decreases, and the chip circuitry automatically compensates for this by increasing the output current, creating a thermal runaway positive feedback loop. However, when the backlight module carries a large current, it can cause overcurrent breakdown and burnout of the LED chips. Furthermore, the generated Joule heat can melt the solder or copper foil circuitry of the LED chips on the LED strip, resulting in an open circuit and uneven brightness distribution in the backlight module.

[0015] To address the aforementioned issues, this application provides an overcurrent protection circuit for an LCD backlight module, which can prevent the compensation current from causing an overload on the backlight module and avoid burning out the backlight module.

[0016] The technical solutions of the embodiments of this application are described in detail below with reference to the accompanying drawings.

[0017] See Figure 1 and Figure 2 An overcurrent protection circuit for an LCD backlight module includes: an input terminal 100, a control module 200, a sampling module 300, and a load module 400. The control module 200 is electrically connected to the input terminal 100. The sampling module 300 includes a MOSFET QT1, a resistor RV1, a resistor R2, a capacitor C1, and a diode DT1. The gate of the MOSFET QT1 is electrically connected to the control module 200, the source of the MOSFET QT1 is electrically connected to the first terminal of the resistor RV1, the second terminal of the resistor RV1 is grounded, the first terminal of the resistor R2 is electrically connected to the control module 200, the second terminal of the resistor R2 is electrically connected to the first terminal of the diode DT1 and the first terminal of the capacitor C1, the second terminal of the diode DT1 is electrically connected to the first terminal of the resistor RV1, and the second terminal of the capacitor C1 is electrically connected to the drain of the MOSFET QT1. The load module 400 is electrically connected to the input terminal and the drain of the MOSFET QT1.

[0018] It should be noted that input 100 is BL_VCC. When the LED chip monitors brightness decay and continuously injects drive current, MOSFET QT1 constantly switches on and off, which plays an overcurrent protection role, preventing the backlight load from burning out due to current overload, and also preventing the LED chip from breaking down due to overcurrent.

[0019] See Figure 2 In one embodiment, the control module 200 includes a resistor R1, with its first end electrically connected to the input terminal and its second end electrically connected to the gate of a MOSFET QT1. Specifically, the control module 200 also includes a transistor QT2, with its collector electrically connected to the second end of resistor R1, its base electrically connected to the first end of resistor R2, and its emitter grounded.

[0020] It should be noted that the BL_VCC voltage input protection circuit has two branches: one is connected to one end of resistor R1, and the other is connected to the LED backlight load. The other end of resistor R1 is connected to the gate of MOSFET QT1 and the collector of transistor QT2. The BL_VCC voltage is applied to the gate of MOSFET QT1 after passing through resistor R1. For the conduction condition of an N-channel MOSFET, the gate voltage must be greater than the drain voltage to turn it on. However, the voltage difference output after the BL_VCC voltage drives the LED backlight load is lower than the gate voltage, so MOSFET QT1 enters the conducting state. At the same time, the BL_VCC voltage provides a driving voltage for the LED backlight load, which is grounded through MOSFET QT1 and the acquisition resistor RV1, forming a complete current loop.

[0021] When the LED backlight load is operating normally, MOSFET QT1 is normally turned on. The backlight load current flows back through the voltage drop Vr formed on the acquisition resistor RV1, and after being unidirectionally conducted by diode DT1, it connects to one end of resistor R2 and one end of capacitor C1. This provides a bias voltage to the base of transistor QT2 while charging capacitor C1 in preparation for subsequent freewheeling operation. Because of the presence of resistor R2, the charging time of capacitor C1 is short. When the LED backlight load current is small, the voltage drop Vr on resistor R1 is also small. Therefore, the base voltage is less than the forward bias turn-on voltage R2V < QT2Ube, and transistor QT2 is in the cut-off state. The BL_VCC voltage cannot be grounded through the collector and can only be transmitted to the gate of MOSFET QT1, making its gate-drain forward conduction. The LED backlight load returns to ground normally, and the overcurrent protection circuit is temporarily in a dormant state.

[0022] When an LCD monitor operates for an extended period, the LED backlight load dissipates its power consumption as heat, and the backlight module has poor heat dissipation. As a result, the junction temperature of the LED backlight load rises sharply. This increase in operating temperature leads to a decrease in the luminous efficiency of the LEDs, a non-linear decay in the luminous flux of the backlight module, and a reduction in the forward conduction voltage Vf of the LED strip. When the LED chip detects the decrease in backlight brightness, it continuously increases the output drive current while maintaining the set backlight brightness, thereby increasing the intensity of the LED backlight load and autonomously enhancing the backlight brightness. As the current of the backlight load increases, the current flowing back through the sampling resistor RV1 will increase, which also reflects the increase in voltage drop Vr. The voltage drop Vr of the sampling resistor RV1 is connected to the resistor R2 after passing through the diode DT1, providing a bias voltage to the base of the transistor QT2. When the voltage drop Vr of the sampling resistor RV1 is greater than or equal to the turn-on voltage between the base and emitter of the transistor QT2 Ube + the conduction voltage of the diode DT1, the transistor QT2 turns on, and the BL_VCC voltage flows from the collector to the emitter ground through the resistor R1. Meanwhile, the voltage at the collector of the transistor QT2 connected to the gate of the MOSFET QT1 is pulled low, and the MOSFET QT1 enters the cut-off state. To maintain the sustaining current of transistor QT2, capacitor C1 discharges and freewheels into resistor R2, providing a conduction buffer for the base of transistor QT2. When the base voltage is lower than the turn-on voltage, transistor QT2 returns to the cut-off state, the collector voltage interrupts the conduction of BL_VCC voltage to ground, and provides voltage to the gate of MOSFET QT1, turning on MOSFET QT1.

[0023] See Figure 2 In one embodiment, the load module 400 includes a plurality of LED groups, the first end of each LED group being electrically connected to the input terminal 100, and the second end of each LED group being electrically connected to the drain of the MOSFET QT1.

[0024] It's understandable that there are multiple LED light groups.

[0025] The solution of this application has been described in detail above with reference to the accompanying drawings. In the above embodiments, the descriptions of each embodiment have different focuses; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. Those skilled in the art should also understand that the actions and modules involved in the specification are not necessarily essential to this application. Furthermore, it is understood that the steps in the method of this application embodiment can be adjusted, combined, and deleted according to actual needs, and the modules in the device of this application embodiment can be combined, divided, and deleted according to actual needs.

[0026] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An overcurrent protection circuit for an LCD backlight module, characterized in that, include: Input terminal; The control module is electrically connected to the input terminal; The sampling module includes a MOSFET QT1, a resistor RV1, a resistor R2, a capacitor C1, and a diode DT1. The gate of the MOSFET QT1 is electrically connected to the control module. The source of the MOSFET QT1 is electrically connected to the first terminal of the resistor RV1, and the second terminal of the resistor RV1 is grounded. The first terminal of the resistor R2 is electrically connected to the control module. The second terminal of the resistor R2 is electrically connected to the first terminal of the diode DT1 and the first terminal of the capacitor C1. The second terminal of the diode DT1 is electrically connected to the first terminal of the resistor RV1. The second terminal of the capacitor C1 is electrically connected to the drain of the MOSFET QT1. The load module is electrically connected to the input terminal and the drain of the MOSFET QT1, respectively.

2. The overcurrent protection circuit for the LCD backlight module according to claim 1, characterized in that, The control module includes a resistor R1, with its first end electrically connected to the input terminal and its second end electrically connected to the gate of the MOS transistor QT1.

3. The overcurrent protection circuit for the LCD backlight module according to claim 2, characterized in that, The control module also includes a transistor QT2, the collector of which is electrically connected to the second end of the resistor R1, the base of which is electrically connected to the first end of the resistor R2, and the emitter of which is grounded.

4. The overcurrent protection circuit for the LCD backlight module according to claim 2, characterized in that, The load module includes several LED groups, with the first end of each LED group electrically connected to the input terminal and the second end of each LED group electrically connected to the drain of the MOSFET QT1.

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