LED Driver Circuit for Backlight Luminance Uniformity and Power Consumption
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Solution Overview
Problem
Existing LED driving circuits face challenges in maintaining uniform luminance with low power consumption when driving a large number of LED elements, particularly in full-array local dimming methods used in backlight devices for display apparatuses.
Innovation Solution
A light-emitting diode (LED) driving circuit that includes a switch-capacitor amplifier circuit, a replica circuit, and an output circuit to sample and amplify input current, providing accurate output current and enabling dimming control through feedback loops and shared current sources, reducing power consumption by sequential sampling and time-division reference current provision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a full-array local dimming method with many LED elements is used, then the luminance uniformity and contrast ratio are improved, but the power consumption increases
Solution Approach 1:
The backlight unit is divided into multiple dimming groups with different luminance levels, allowing selective dimming of specific regions. The LED driving circuit is segmented into multiple pixel circuits, each controlling a dimming group independently, enabling localized brightness control without increasing overall power consumption.
Solution Approach 2:
The LED driving circuit uses periodic sampling of reference current in alternating periods (first period for sampling, second period for output). This time-division multiplexing approach allows the circuit to maintain accurate current control while reducing average power consumption by keeping circuits in low-power states during non-active periods.
2Illumination intensity
If many LED elements are driven simultaneously, then the luminance uniformity is improved, but the accuracy of output current control deteriorates
Solution Approach 1:
The circuit performs preliminary sampling of the reference current during the first period before generating the output current in the second period. This advance sampling allows the switch-capacitor amplifier to prepare accurate voltage levels in advance, ensuring precise current control when the output stage activates.
Solution Approach 2:
A feedback loop is implemented where the output current is monitored and fed back to the switch-capacitor amplifier circuit. This feedback mechanism compensates for variations in LED forward voltage and ensures accurate current control, maintaining luminance uniformity across all LED elements.
3Use of energy by moving object
If a simple LED driving circuit is used, then the power consumption is reduced, but the accuracy of output current and uniformity of brightness deteriorates
Solution Approach 1:
Multiple functions are merged into a single integrated pixel circuit: the switch-capacitor amplifier, replica circuit for offset compensation, and output driver are combined in one circuit block. This integration reduces the number of separate components and power domains while maintaining high current control accuracy through shared reference current sampling.
Solution Approach 2:
The circuit dynamically changes operating parameters between periods: during the first period, the switch-capacitor amplifier samples and stores voltage parameters; during the second period, these parameters are converted to precise current output. The replica circuit adjusts compensation parameters based on sampled offset values, maintaining accuracy across varying operating conditions.
Data Source
AI summary
A light-emitting diode (LED) driving circuit for driving an LED channel including a plurality of LED elements includes a switch-capacitor amplifier circuit configured to sample received input current and amplify an input voltage corresponding to the input current, a replica circuit configured to connect to the switch-capacitor amplifier circuit in a first period to define a first feedback loop, and an output circuit configured to connect to the switch-capacitor amplifier in a second period to define a second feedback loop. The second period is after the first period, and the output circuit is configured to generate output current according to an output voltage of the switch-capacitor amplifier circuit and provide the output current to the LED.