Backlight Module Detecting Abnormal Lamp Tubes
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Solution Overview
Problem
Current LCD backlight systems using Cold Cathode Fluorescent Lamps (CCFLs) face issues with uneven brightness and display quality due to increased current leakage with longer lamp lengths and higher operating voltages, and lack effective protection against malfunctioning lamp tubes or poorly soldered ballast capacitors.
Innovation Solution
A backlight module with a dual-transformer configuration and detecting circuits to apply differential driving voltages to CCFL ends, a comparator to generate a protection signal for abnormal conditions, and a voltage calculator to adjust the supply voltage based on detected anomalies, enabling real-time protection and improved brightness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single transformer with ballast capacitors is used to activate lamp tubes, then design costs are reduced and simplicity is achieved, but the protection circuit cannot perform its function when lamp tubes malfunction or ballast capacitors crack/poorly soldered
Solution Approach 1:
The patent divides the single transformer into two separate transformers, with each transformer dedicated to driving one lamp tube. This segmentation allows independent protection circuits for each lamp tube, enabling reliable detection and protection even when one lamp tube malfunctions or ballast capacitors fail, thus resolving the contradiction between manufacturing simplicity and protection reliability.
Solution Approach 2:
The patent introduces protection circuits as intermediary components between the transformers and lamp tubes. These protection circuits monitor the status of lamp tubes and ballast capacitors, and can disconnect the lamp tubes from the power supply when abnormalities are detected, thereby ensuring reliable protection while maintaining the cost-effective dual-transformer configuration.
2Power
If higher operating voltage is applied to longer CCFL, then the lamp tube can be activated, but current leakage increases non-linearly
Solution Approach 1:
The patent segments the CCFL into two parts by using two separate transformers, with each transformer driving one end of the lamp tube. This segmentation allows the use of lower operating voltages for each segment compared to driving the entire long CCFL with a single high voltage, thereby reducing current leakage while still enabling the lamp tube to function properly.
3Power
If high frequency driving voltage is applied to one end of CCFL, then the lamp tube can be activated, but current decreases with distance from the high voltage end causing uneven display quality
Solution Approach 1:
The patent applies segmentation by using two transformers to drive both ends of the CCFL with balanced voltages. This eliminates the current decrease with distance problem by ensuring both ends of the lamp tube receive adequate driving voltage, thereby achieving uniform current distribution and improved display quality consistency across the entire screen.
4Reliability
If dual transformer configuration is used, then current balance and protection are improved, but device complexity increases
Solution Approach 1:
The patent employs parameter changes by using two transformers with different turns ratios to drive the two ends of the CCFL. By adjusting the turns ratio parameters of the transformers, the system achieves current balance and proper voltage distribution without requiring complex control circuits, thus improving reliability while limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively detects and responds to abnormal lamp tube or ballast capacitor conditions, ensuring consistent display quality and safety by adjusting the supply voltage and activating protective functions, thereby reducing current leakage and enhancing operational reliability.
Implementation Method 1
a first transformer electrically connected to the first end of the lamp tube, for converting the supply voltage into a first driving voltage signal, and outputting the first driving voltage signal to the first end of the lamp tube
Implementation Method 2
a second transformer electrically connected to the second end of the lamp tube for converting the supply voltage into a second driving voltage signal, and outputting the second driving voltage signal to the second end of the lamp tube
Implementation Method 3
The CCFL can emit light when noble gas inside the lamp is driven by a high-frequency driving voltage
Data Source
AI summary
A backlight module detecting abnormal lamp tubes and an LCD employing such a backlight module are proposed. The LCD includes a voltage calculator for detecting voltage applied on ends of a lamp tube to monitor the lamp tube. Once the lamp tube becomes abnormal, the voltage varies accordingly. The voltage calculator calculates a voltage signal from a plurality of lamp tubes and produces a voltage value. A protection circuit regards the voltage value as a feedback signal to decide if there are any abnormalities. Once any of the lamp tubes is abnormal, the protection circuit transmits the voltage signal to a pulse-width modulated integrated circuit (PWM IC) to activate a protective function. The protection circuit of the present invention obtains the protection signal by sampling the voltage signal of the ends of the lamp tube and then gets the control signal by means of the calculation of the voltage calculator. Thus, voltage level retrieved from the protection signal are less easily affected by dimming and temperature.