Multi-string LED Backlight Current Balancing via PWM Control
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Solution Overview
Problem
Balancing current in multi-string LED circuits for backlighting in large displays is challenging due to variations in LED voltages and types, leading to inefficient power consumption and potential damage from excess current.
Innovation Solution
The solution involves selecting the string with the highest forward voltage as the lead string and maintaining it in continuous current mode, while switching other strings to pulse width modulation (PWM) mode to ensure only predetermined currents flow, thereby optimizing power supply and reducing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple LED strings are used to provide adequate backlight for large displays, then sufficient illumination is achieved, but current balancing becomes difficult due to voltage variations among strings
Solution Approach 1:
The patent divides the LED backlight system into multiple independent strings, each with its own current control circuit. This segmentation allows individual control of each string's current, enabling precise current balancing across all strings despite voltage variations, thereby maintaining uniform illumination across the large display.
Solution Approach 2:
The patent implements feedback control by measuring the actual current in each LED string and using this information to adjust the drive signal. The current sense resistor and control circuit continuously monitor and regulate current distribution, ensuring that each string receives the appropriate current to maintain balanced illumination across the display.
2Illumination intensity
If higher current is supplied to ensure sufficient brightness, then illumination intensity increases, but power consumption increases and potential damage from excess current occurs
Solution Approach 1:
The patent employs dynamic current control where the current supplied to each LED string is continuously adjusted based on real-time measurements and display brightness requirements. This dynamic regulation ensures that LEDs receive only the necessary current to achieve the desired brightness level, preventing excessive power consumption and potential damage from over-current conditions.
Solution Approach 2:
The patent changes the current parameter dynamically by using pulse width modulation (PWM) and analog dimming techniques to precisely control the average current through each LED string. This allows the system to optimize power consumption by supplying lower currents during normal operation while maintaining the capability to increase current when higher brightness is required.
3Stability of the object's composition
If analog current mode is used for continuous control, then current stability is improved, but power dissipation increases compared to switching modes
Solution Approach 1:
The patent uses periodic switching action in the form of pulse width modulation (PWM) to control LED current. By rapidly switching the current on and off at a frequency higher than the human eye can detect, the system achieves effective current control with reduced power dissipation compared to continuous analog control, while maintaining perceived current stability through the averaging effect of the PWM cycle.
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
This approach ensures stable and adjustable current distribution across LED strings, minimizing power consumption and preventing damage from excess current, while maintaining sufficient brightness and stability for display illumination.
Implementation Method 1
The display industry is enthusiastically perusing the use of LEDs as the light source in the backlight technology
Data Source
AI summary
The present invention relates to displays that use LED strings for backlighting. A lead string is provided with continuous drive voltage and the non-lead strings are provided with pulsed drive pulses. The string having the highest forward voltage is selected as the lead string. Feedback information indicative of the currents flowing through the non-lead strings is used to determine the duty cycles of the voltage pulses provided to drive the non-lead strings. The non-lead strings are controlled using pulsed drive voltages to minimize power dissipation in the circuit.