Backlight Driving Device Headroom Voltage Control
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Solution Overview
Problem
The variability in forward voltage across semiconductor light-emitting strings in backlight devices leads to uneven headroom voltages, causing heat generation and altering circuit characteristics, which reduces reliability and increases power consumption.
Innovation Solution
A light-emitting driving device with a sensing circuit, PWM signal generation circuit, and controller that adjusts the intensity of the driving current and duty ratio of the PWM signal based on sensed channel terminal voltages to maintain a consistent headroom voltage near the minimum value, preventing heat generation and ensuring reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the forward voltage of semiconductor light-emitting elements varies across light-emitting strings, then the headroom voltage at channel terminals becomes distributed in various ways, but this causes heat generation and changes in circuit characteristics
Solution Approach 1:
The patent implements a feedback mechanism where the sensing circuit continuously monitors the headroom voltage at channel terminals and feeds this information back to the controller. The controller then adjusts the driving current intensity and PWM duty ratio based on the sensed voltage, creating a closed-loop control system that maintains stable circuit characteristics and prevents excessive heat generation.
Solution Approach 2:
The patent makes the driving current intensity and PWM duty ratio dynamic rather than fixed. The controller continuously adjusts these parameters based on real-time headroom voltage measurements, allowing the system to adapt to variations in forward voltage across different light-emitting strings and maintain optimal operating conditions.
2Temperature
If the headroom voltage is reduced to prevent heat generation, then circuit characteristics remain stable, but the driving current must be precisely controlled to maintain constant luminance
Solution Approach 1:
The patent combines multiple control functions into a single integrated controller that simultaneously manages driving current intensity and PWM duty ratio based on headroom voltage feedback. This unified control approach manages the complexity by coordinating multiple control actions through one control unit rather than requiring separate control circuits for each parameter.
Solution Approach 2:
The patent changes the control parameters from fixed values to dynamically adjustable parameters. The controller modifies driving current intensity and PWM duty ratio based on real-time headroom voltage measurements, allowing the system to maintain stable operation with reduced heat generation while adapting to variations in light-emitting string characteristics.
3Illumination intensity
If the driving current intensity is increased to compensate for high forward voltage, then light emission is maintained, but power consumption increases
Solution Approach 1:
The patent employs dynamic control of driving current intensity and PWM duty ratio based on real-time headroom voltage measurements. Rather than using a fixed high current to compensate for all forward voltage variations, the system dynamically adjusts current levels to match actual needs, maintaining light emission while minimizing power consumption.
Solution Approach 2:
The patent uses PWM (Pulse Width Modulation) to control light emission, where the driving current is applied in periodic pulses rather than continuously. By adjusting the duty ratio of these pulses, the system maintains average luminance while reducing overall power consumption, as the current is only applied when needed for light emission.
Data Source
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Figure 5A~6B
AI summary
The light-emitting driving device includes a driving current generation circuit, a sensing circuit, a PWM signal generation circuit, and a controller. The driving current generation circuit can be connected to a channel terminal of a light-emitting string including a plurality of semiconductor light-emitting elements to generate a driving current supplied to the channel terminal. The sensing circuit is connected to the channel terminal to sense a voltage of the channel terminal. The PWM signal generation circuit can generate a PWM signal that controls the supply of driving current. The controller is connected to the sensing circuit to control at least one or more of the intensity of the driving current and the duty ratio of the PWM signal based on the sensed voltage of the channel terminal.