Backlight Device Staggered LED Drive Timing
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Solution Overview
Problem
In backlight devices for liquid crystal display apparatuses, simultaneous changes in LED drive current by multiple LED drive circuits can lead to increased inrush current and power supply voltage drops, causing LED elements to turn off and potentially destabilizing the operation of FETs in the drive circuits.
Innovation Solution
The implementation of a control circuit and time constant circuits that delay the vertical synchronization signal by a predetermined time, allowing each LED drive circuit to adjust its current independently and reducing the likelihood of simultaneous changes in LED drive current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If multiple LED drive circuits simultaneously change LED drive current in synchronization with vertical synchronization signal, then local dimming control is achieved, but inrush current increases and power supply voltage drops
Solution Approach 1:
The patent applies periodic action by sequentially controlling different LED drive circuits in different horizontal scanning periods instead of simultaneously changing all LED drive currents. The control circuit divides the display region into multiple regions and controls LED drive circuits corresponding to different regions in different horizontal scanning periods, thereby periodicallly distributing the current changes and avoiding simultaneous inrush current accumulation.
2Reliability
If power supply voltage of LED is set high to avoid turning off, then LED operation stability is improved, but power consumption increases and FET heat generation worsens
Solution Approach 1:
The patent applies preliminary action by sequentially enabling different LED drive circuits in different horizontal scanning periods before the liquid crystal display panel completes a full vertical scanning period. This timing arrangement ensures that LED current changes are distributed over time, allowing the power supply voltage to remain stable at normal levels without requiring excessively high voltage settings, thus avoiding increased power consumption and FET heat generation.
3Reliability
If DCDC circuit is designed with good transient response characteristics to stabilize power supply voltage, then power supply voltage stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies segmentation by dividing the display region into multiple regions and controlling LED drive circuits corresponding to different regions in different horizontal scanning periods. This segmentation of control timing distributes the load changes over time, reducing the transient response requirements for the DCDC circuit and allowing for simpler, lower-cost circuit designs while maintaining power supply voltage stability.
Data Source
AI summary
A backlight device includes: a plurality of LED elements arranged in a plurality of regions including a first region and a second region; a plurality of LED drive circuits configured to generate LED drive signals configured to drive the LED elements; a control circuit configured to outputs a vertical synchronization signal and current setting data configured to set luminance of the LED elements; and a time constant circuit that delays the vertical synchronization signal by a predetermined time. The LED drive circuits includes a first LED drive circuit associated with the LED elements in the first region. The time constant circuit includes a first time constant circuit connected to the first LED drive circuit. The first LED drive circuit is configured to receive the current setting data output from the control circuit and receive the first vertical synchronization signal delayed by the first time constant circuit.