Backlight circuit of display screen

Abstract

The utility model relates to the technical field of display circuits, and discloses a backlight circuit of a display screen, which aims to solve the technical problem of poor display effect caused by insufficient stability of the backlight circuit of the existing display screen, and is characterized in that the output end of a driver U4 is connected with a power switch tube Q10, a current limiter U5 is an operational amplifier, and the power switch tube Q10 is connected with the current limiter U5; the output end of the driver U4 is connected with the base electrode of the power switch tube Q10, the emitting electrode of the power switch tube Q10 is grounded through the current detection resistor R15, and the upper end and the lower end of the current detection resistor R15 are connected with the inverted input end and the in-phase output end of the current limiter U5 respectively. And an inductor L2 and a diode D8 are arranged, one end of the inductor L2 is used for inputting an external power supply VCC, the other end of the inductor L2 is connected with a collector electrode of the power switch tube Q10 and an anode of the diode D8, and a cathode of the diode D8 is used as an anode output end of the backlight power supply. The stability and safety of the circuit are improved, and the brightness uniformity of the display screen and the visual experience of a user are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of display circuits, in particular to a backlight circuit of a display screen. Background Art

[0002] With the continuous development of display technology, the performance and image quality requirements of display screens are gradually increasing. Among them, the backlight system, as a key component of the display, has a significant impact on the display effect. Currently, backlight circuits generally use pulse width modulation (PWM) control to adjust the brightness. By controlling the switching frequency and brightness of the LED backlight, the stability of the display at different brightness levels is ensured. However, traditional PWM control backlight circuits may face the following problems:

[0003] Insufficient overcurrent protection: When the load current exceeds the preset value, traditional circuits cannot effectively limit the current in a timely manner, which may cause damage to power devices and affect the overall safety and reliability of the circuit.

[0004] Lack of overvoltage protection: When the input voltage is too high, circuits without overvoltage protection may experience transient voltage surges, causing overheating or damage to components.

[0005] Poor output voltage stability: When facing load fluctuations, the output voltage stability of traditional circuits is poor, resulting in uneven backlight brightness and affecting the display effect of the display.

[0006] Current ripple impact: Excessive LED current ripple may cause brightness fluctuations and affect the visual experience.

[0007] In summary, the existing display backlight circuit has technical defects in terms of safety and output stability, and an improved backlight circuit is needed to achieve an efficient and stable backlight driving effect. Utility Model Content

[0008] The purpose of the utility model is to provide a backlight circuit for a display screen, so as to solve the technical problem that the existing backlight circuit for a display screen is not stable enough and thus causes poor display effects.

[0009] To achieve the above objectives, the specific technical solution of a backlight circuit of a display screen of the present invention is as follows:

[0010] A backlight circuit for a display screen includes a PFM controller U2, which is connected to an oscillator U6, an error amplifier U1, a driver U4, and a current limiter U5. The output end of the driver U4 is connected to a power switch tube Q10. The current limiter U5 is an operational amplifier. The output end of the driver U4 is connected to the base of the power switch tube Q10. The emitter of the power switch tube Q10 is grounded via a current-sense resistor R15. The first end of the current-sense resistor R15 is connected to the emitter of the power switch tube Q10. The second end of the current-sense resistor R15 is grounded. The upper and lower ends of the current-sense resistor R15 are respectively connected to the inverting input and non-inverting output of the current limiter U5. An inductor L2 and a diode D8 are provided. One end of the inductor L2 is used to input an external power supply VCC, and the other end of the inductor L2 is respectively connected to the collector of the power switch tube Q10 and the anode of the diode D8. The cathode of the diode D8 serves as the positive output end of the backlight power supply.

[0011] Current limiter U5 monitors the current flowing through power switch Q10 in real time. When the current exceeds a set safety threshold, current limiter U5 limits the output of driver U4, thereby controlling the conduction of power switch Q10 and suppressing excessive current. This design effectively prevents damage to power switch Q10 or other components caused by overcurrent, extending circuit life and ensuring stable backlight power supply output.

[0012] Traditional backlight circuits are prone to overcurrent and component damage when current fluctuates or exceeds limits. This current protection design effectively solves this problem and improves circuit reliability.

[0013] Through the feedback mechanism of error amplifier U1, PFM controller U2 adjusts the drive signal in real time based on changes in the output voltage, thereby controlling the on-time of power switch Q10 to achieve a regulated output voltage. The combination of inductor L2 and diode D8 further smooths voltage variations, allowing the backlight circuit to maintain a stable output despite input voltage fluctuations, thereby improving the brightness stability of the display.

[0014] Traditional backlight circuits are prone to uneven brightness or flickering when voltage fluctuates. This voltage-stabilizing control design effectively solves the output voltage stability issue, ensuring uniform brightness of the display backlight.

[0015] The design of inductor L2 and diode D8 effectively achieves voltage conversion and energy storage. Inductor L2 stores energy during the on-time of power switch Q10 and releases it during off-time. Together with diode D8, this energy conversion mechanism not only improves the backlight circuit's energy utilization but also reduces heat generation caused by power loss, thereby enhancing overall circuit efficiency.

[0016] Conventional backlight circuits are inefficient in energy conversion, resulting in high power consumption and heat generation. This design addresses this power loss issue by optimizing the energy conversion structure, enhancing the circuit's energy-saving performance.

[0017] The combination of diode D8 and inductor L2 effectively suppresses current ripple, ensuring a stable output current and preventing excessive current ripple from affecting the LED brightness. This not only improves the brightness stability of the LED backlight but also enables the display to maintain consistent visual effects even during extended periods of operation, improving the user's visual experience.

[0018] Excessive current ripple can cause unstable backlight brightness or display flicker, affecting visual quality. This design eliminates the flickering issue by suppressing current ripple, improving the user experience.

[0019] This backlight circuit's design comprehensively considers current protection, voltage regulation, efficient energy conversion, and ripple suppression, successfully resolving issues such as overcurrent, unstable output voltage, low energy efficiency, and current ripple interference found in traditional backlight circuits. This design not only enhances circuit stability and safety, but also improves the display's brightness uniformity and the user's visual experience.

[0020] Furthermore, the negative output terminal of the backlight power supply is grounded via a resistor R18, a resistor R19 and a capacitor C10 connected in parallel.

[0021] Furthermore, the resistance values ​​of the resistor R18 and the resistor R19 are both 10 ohms, and the capacitance value of the capacitor C10 is 0.1 uF.

[0022] Furthermore, the cathode of the diode D8 is connected to the backlight via the resistor R17 , and the cathode of the diode D8 is grounded via the capacitor C9 .

[0023] Furthermore, the resistance of the resistor R17 is 0 ohm, and the capacitance of the capacitor C9 is 4.7 uF.

[0024] Furthermore, the error amplifier U1 is grounded through the capacitor C5, and the inverting input terminal of the error amplifier U1 is connected to the negative output terminal of the backlight power supply through the current limiting resistor R12. The inverting input terminal of the error amplifier U1 is also provided with a Zener diode Z1, the anode of the Zener diode Z1 is connected to the inverting input terminal of the error amplifier U1, and the cathode of the Zener diode Z1 is connected to the external input power supply through the resistor R16.

[0025] A voltage regulator diode Z1 is placed at the inverting input of error amplifier U1 and connected to the negative output terminal via a current-limiting resistor R12. When the input voltage exceeds the set overvoltage threshold, voltage regulator diode Z1 activates the overvoltage protection mechanism, limiting the inverting input voltage of error amplifier U1. This reduces the output amplitude of the error amplifier and shuts down the PFM controller U2, preventing circuit damage due to excessive voltage. This design effectively ensures circuit safety, preventing component damage caused by excessive input voltage, and improves output voltage reliability through stable voltage feedback.

[0026] The backlight circuit of a display screen provided by the utility model has the following advantages:

[0027] The backlight circuit for a display screen provided by the present invention achieves multiple beneficial effects by integrating a PFM controller, oscillator, error amplifier, driver, and current limiter, combined with the optimized design of inductors and diodes. The current limiter can monitor and limit the current of the power switch tube in real time, preventing damage to components caused by overcurrent, thereby improving the reliability and service life of the circuit. The feedback mechanism of the error amplifier and PFM controller effectively controls the output voltage, ensuring the stability of the backlight brightness when the input voltage fluctuates, avoiding the brightness flickering problem caused by voltage instability in traditional circuits. The combination of inductors and diodes not only improves voltage conversion efficiency, reduces power loss and heat generation, thereby improving the energy utilization and energy-saving performance of the circuit, but also effectively suppresses current ripple, ensuring a stable output current, avoiding problems such as unstable brightness or display screen flickering, and improving the user's visual experience. The overall design has improved current protection, stable output voltage, efficient energy conversion, and ripple suppression, successfully solving the problems of overcurrent, unstable output voltage, low energy efficiency, and current ripple in traditional backlight circuits, significantly improving the stability and safety of the circuit, the brightness uniformity of the display screen, and the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The backlight circuit diagram of the display screen provided by the utility model;

[0029] Figure 2 This is a basic circuit structure diagram of the backlight board provided by the utility model.

[0030] In the figure: U1, error amplifier; U2, PFM controller; U4, driver; U5, current limiter; U6, oscillator; Q10, power switch tube. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] See Figure 1 The utility model provides a backlight circuit for a display screen, including a PFM controller U2. The PFM controller U2 is respectively connected to an oscillator U6, an error amplifier U1, a driver U4 and a current limiter U5. The output end of the driver U4 is connected to a power switch tube Q10.

[0033] The power switch tube Q10 is a triode, the current limiter U5 is an operational amplifier, the output end of the driver U4 is connected to the base of the power switch tube Q10, the emitter of the power switch tube Q10 is grounded through the current sensing resistor R15, the first end of the current sensing resistor R15 is connected to the emitter of the power switch tube Q10, the second end of the current sensing resistor R15 is grounded, the first end of the current sensing resistor R15 is connected to the inverting output end of the current limiter U5, and the second end of the current sensing resistor R15 is connected to the non-inverting output end of the current limiter U5.

[0034] The external input power supply VCC is connected to the collector of the power switch Q10 through resistor R16 and inductor L2. The collector of the power switch Q10 is connected to diode D8, which serves as the positive output terminal of the backlight power supply. The negative output terminal of the backlight power supply is connected to ground through parallel resistors R18, R19, and capacitor C10. The resistance values ​​of resistors R18 and R19 are both 10 ohms, and the capacitance of capacitor C10 is 0.1uF.

[0035] Specifically, the anode of diode D8 is connected to the collector of power switch Q10, while the cathode of diode D8 is connected to the backlight via resistor R17. The cathode of diode D8 is grounded via capacitor C9. Resistor R17 is a 0 ohm resistor, and capacitor C9 is 4.7 uF. The smaller the value of capacitor C9, the greater the LED current ripple.

[0036] The error amplifier U1 is grounded through the capacitor C5, and the inverting input terminal of the error amplifier U1 is connected to the negative output terminal through the current limiting resistor R12. A voltage regulator Z1 is provided, and the anode of the voltage regulator Z1 is connected to the inverting input terminal of the error amplifier U1, and the cathode of the voltage regulator Z1 is connected to the external input power supply through the resistor R16.

[0037] Zener diode Z1 provides overvoltage protection. When the voltage exceeds the set overvoltage threshold, the protection mechanism is activated to prevent circuit damage due to excessive voltage. The specific principle is that excessive voltage is applied to the inverting output of the error amplifier, which reduces the output amplitude of the error amplifier, causing the PFM controller U2 to shut down.

[0038] At the same time, the inverting input of error amplifier U1 also serves as the feedback voltage input. Error amplifier U1 compares the feedback voltage at the inverting input with an internal 200mV reference voltage to generate an error signal. This error signal is used to control PFM (pulse width modulation) controller U2.

[0039] PFM controller U2 adjusts the duty cycle of the pulse-width modulation signal based on the signal output by the error amplifier to control the on and off of the power switch tube, achieving a regulated output voltage. PFM controller U2 is also connected to the oscillator module U6, providing a clock signal to control the switching frequency.

[0040] The current limiter U5, consisting of an operational amplifier, protects the entire circuit and load by detecting the current flowing through the power switch. When the current exceeds a preset limit, the current limiter U5 limits the output of the drive signal and feeds it back to the PFM controller U2, thereby limiting the current flowing through the power switch Q10 and preventing overcurrent.

[0041] Driver U4 amplifies the output signal of PFM controller U2 and drives power switch Q10. The emitter of the power switch is grounded, and the collector is connected to the common terminal of inductor L2 and diode D8, providing the primary path for the load current. By controlling the on / off state of power switch Q10, the output voltage is stabilized.

[0042] The overall operating principle is as follows: the input voltage is output through inductor L2 and diode D8. PFM controller U2 and driver U4 control the on / off state of power switch Q10 to stabilize the output voltage at the desired value. When the inverting input of error amplifier U1 detects changes in the output voltage, error amplifier U1 adjusts the output signal of PFM controller U2, thereby adjusting the on-time of power switch Q10 to maintain a stable output voltage. At the same time, overvoltage protection and current limiting modules ensure safe circuit operation.

[0043] Figure 2 It is a combination of light-emitting diodes in the backlight source. The light-emitting diodes are connected in series and parallel and connected to the positive output terminal and the negative output terminal of the backlight power supply to emit light.

[0044] The beneficial effects of implementing the backlight circuit of a display screen provided by the present invention are as follows:

[0045] This utility model provides an improved display screen backlight circuit. By adopting modules such as a PFM controller, a current limiter, and an error amplifier, it effectively solves the problems of overcurrent protection, overvoltage protection, and poor output voltage stability in traditional backlight circuits. The specific beneficial effects are as follows:

[0046] Current limiter U5 monitors the current of power switch Q10. When the current exceeds a preset limit, it limits the output of the drive signal and feeds it back to PFM controller U2, thereby limiting the current of power switch Q10. This overcurrent protection mechanism effectively prevents circuit damage due to overcurrent, improving circuit safety and reliability.

[0047] This circuit uses a Zener diode Z1 as an overvoltage protection element. When the input voltage exceeds the set threshold, the Zener diode Z1 activates its protection mechanism, feeding the excessive voltage back to the error amplifier U1, thereby reducing the error amplifier's output amplitude and shutting down the PFM controller U2, thus preventing component damage caused by excessive voltage.

[0048] This circuit uses error amplifier U1 to monitor the output voltage in real time and compare the feedback voltage with an internal reference voltage to generate an error signal that controls the output of PFM controller U2. Based on this error signal, PFM controller U2 adjusts the on-time of power switch Q10 to maintain a stable output voltage, ensuring a uniform display across varying brightness levels.

[0049] This circuit controls the LED current ripple by adjusting the capacitance of capacitor C9, ensuring the stability of the output current and reducing the impact of current ripple on brightness uniformity, thereby improving the visual effect.

[0050] In summary, the backlight circuit provided by the present invention not only solves the shortcomings of traditional circuits in overcurrent, overvoltage protection and stability, but also ensures the stable lighting of the LED through precise current ripple control, thereby improving the brightness consistency and visual experience of the display screen.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A backlight circuit for a display screen, comprising a PFM controller U2, characterized in that: The PFM controller U2 is respectively connected to an oscillator U6, an error amplifier U1, a driver U4 and a current limiter U5. The output end of the driver U4 is connected to a power switch tube Q10. The current limiter U5 is an operational amplifier. The output end of the driver U4 is connected to the base of the power switch tube Q10. The emitter of the power switch tube Q10 is grounded through a current-sense resistor R15. The upper and lower ends of the current-sense resistor R15 are respectively connected to the inverting input end and the non-inverting output end of the current limiter U5; an inductor L2 and a diode D8 are provided. One end of the inductor L2 is used to input an external power supply VCC, and the other end of the inductor L2 is respectively connected to the collector of the power switch tube Q10 and the anode of the diode D8. The cathode of the diode D8 is used as the positive output end of the backlight power supply.

2. The backlight circuit of a display screen according to claim 1, characterized in that: The negative output terminal of the backlight power supply is grounded via a resistor R18, a resistor R19 and a capacitor C10 connected in parallel.

3. The backlight circuit of the display screen according to claim 2, characterized in that: The resistance values ​​of the resistor R18 and the resistor R19 are both 10 ohms, and the capacitance value of the capacitor C10 is 0.1 uF.

4. The backlight circuit of a display screen according to claim 2, characterized in that: The cathode of the diode D8 is connected to the backlight via the resistor R17 , and the cathode of the diode D8 is grounded via the capacitor C9 .

5. The backlight circuit of the display screen according to claim 4, characterized in that: The resistance of the resistor R17 is 0 ohm, and the capacitance of the capacitor C9 is 4.7 uF.

6. The backlight circuit of a display screen according to claim 1, characterized in that: The error amplifier U1 is grounded via a capacitor C5, and the inverting input terminal of the error amplifier U1 is connected to the negative output terminal of the backlight power supply via a current-limiting resistor R12. A voltage regulator Z1 is also provided at the inverting input terminal of the error amplifier U1, and the anode of the voltage regulator Z1 is connected to the inverting input terminal of the error amplifier U1, and the cathode of the voltage regulator Z1 is connected to the external input power supply via the resistor R16.

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