Backlight PWM Phase Shifting Reduces Peak Current
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Solution Overview
Problem
The increasing demand for high brightness in display devices with backlight units, particularly during short light-on times, leads to excessive load on light source units and higher current capacity requirements, increasing costs and power supply unit loads.
Innovation Solution
A display device with a backlight unit comprising two light source units and a control unit that outputs PWM signals with shifted phases to manage the overlapped drive periods, reducing the peak current requirement by 30% and preventing simultaneous on-states, thus decreasing the necessary current capacity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If light emitting diodes are driven at the same timing with predetermined brightness during one frame period, then noise can be reduced, but the current capacity required for driving increases due to overlapped periods
Solution Approach 1:
The patent applies periodic action by sequentially driving different groups of light emitting diodes in alternating periods within one frame period. First light emitting diodes are driven in a first period, then second light emitting diodes are driven in a second period, creating a periodic driving pattern that eliminates simultaneous operation and reduces current capacity requirements while maintaining noise reduction benefits
Solution Approach 2:
The patent segments the light emitting diodes into multiple groups (first light emitting diodes and second light emitting diodes) that are driven at different times. This segmentation allows the total current load to be distributed across different time periods rather than all diodes drawing current simultaneously, thereby reducing the required current capacity
2Measurement precision
If high brightness in short light on time is demanded for each light source unit, then display resolution improves, but the load on light source units becomes excessive
Solution Approach 1:
The patent uses periodic action by providing black insertion periods within the frame period where light source units are turned off. This creates alternating periods of high brightness operation and rest, allowing the display to achieve high resolution through precise timing while reducing the cumulative load on light source units over time
Solution Approach 2:
The patent applies partial action by not continuously operating light source units at maximum capacity. Instead, high brightness is provided only during necessary display periods, with black insertion periods providing rest, thereby achieving the required display resolution without subjecting light source units to excessive continuous load
3Illumination intensity
If a power supply unit with current capacity matching the overlapped period is provided, then brightness requirements are met, but the cost increases
Solution Approach 1:
The patent applies periodic action by sequentially operating different light source units in different periods rather than all units operating simultaneously. This time-division approach allows the use of a power supply unit with lower current capacity since the maximum current draw at any given moment corresponds to only one group of light source units, thereby reducing manufacturing cost while maintaining required brightness levels
Solution Approach 2:
The patent segments light source units into multiple groups that operate at different times. This segmentation allows the power supply unit to be sized for the peak current of a single group rather than the sum of all groups, reducing the required current capacity and associated manufacturing cost while still meeting brightness requirements during active periods
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 configuration effectively reduces the current capacity and manufacturing costs for the power supply unit while maintaining brightness levels, alleviating load fluctuations and enabling high video resolution.
Implementation Method 1
outputs a PWM signal as the drive signal to the first light source unit in the overlapped period, and a PWM signal as the drive signal to the second light source unit in the overlapped period, each of the PWM signals turning the first light source unit and the second light source unit on and off with a predetermined pulse width
Data Source
AI summary
A display device has a display panel and a backlight unit. The backlight unit includes first and second light source units, and a control unit that outputs a drive signal to the light source units to drive the first and second light source units during first and second drive periods in one frame period respectively. The control unit drives the light source units so that the one frame period has an overlapped period, in which the first and second drive periods overlap. The control unit outputs PWM signals to turn the light source units on and off to the light source units respectively. The control unit shifts a phase of the PWM signal to be outputted to the first light source unit and a phase of the PWM signal to be outputted to the second light source unit from each other.