LCD Power Supply Circuit Spread Spectrum EMI Reduction
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Solution Overview
Problem
Conventional liquid crystal display devices experience severe electromagnetic interference (EMI) and unstable image display due to fixed phases of charging and loading control signals used in power supply circuits for generating gate voltages, leading to concentrated spectral bands and frame instability.
Innovation Solution
The power supply circuit periodically or irregularly changes the durations of charging and loading control signals, ensuring they have the same phase at the start of each frame, utilizing capacitors and switches to manage charge distribution and output control signals in a spread spectrum pattern, thereby reducing EMI and stabilizing image display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charging control signals and loading control signals are output with fixed phases, then the power supply circuit can generate stable gate voltages, but electromagnetic interference becomes severe and spectral energy concentrates at specific frequencies
Solution Approach 1:
The patent applies dynamics by making the charging and loading control signals variable rather than fixed. Specifically, the durations of these control signals are dynamically adjusted using a duty cycle adjustment unit that modifies the on-time of switching elements based on feedback from a spectrum analyzer. This dynamic adjustment spreads the spectral energy across a wider frequency range, reducing electromagnetic interference while maintaining stable gate voltage generation through closed-loop control.
Solution Approach 2:
The patent changes the temporal parameters of the control signals by adjusting their durations and duty cycles. The duty cycle adjustment unit modifies the proportion of time switching elements remain in the on-state, thereby changing the effective duration of charging and loading phases. This parameter modification spreads spectral energy density and reduces concentration at specific frequencies, mitigating electromagnetic interference while preserving voltage stability.
2Adaptability or versatility
If charging control signals and loading control signals are output with different phases during frame transitions, then the power supply can adapt to varying load conditions, but image display becomes unstable
Solution Approach 1:
The patent employs feedback control to monitor and adjust the phases of charging and loading control signals during frame transitions. A phase detection unit monitors the timing relationships between control signals and frame synchronization signals, and a phase adjustment unit modifies the phases accordingly. This feedback mechanism ensures that control signals are properly synchronized at frame boundaries, maintaining stable image display while still allowing phase variation during steady-state operation to adapt to different load conditions.
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 effectively suppresses electromagnetic interference and ensures stable image display by spreading the spectral energy, preventing power waste and maintaining consistent driving voltages across frames.
Implementation Method 1
a first capacitor having both ends connected to a positive power terminal and a negative power terminal through first and second switches, thereby charging a charge
Data Source
AI summary
A power supply circuit of a liquid crystal display device includes a first positive polarity charge charging unit including a first capacitor connected to positive and negative power terminals through switches to charge a charge, a second positive polarity charge charging unit including a second capacitor connected to the positive power terminal and a ground terminal through switches to charge a charge, a first positive polarity charge loading unit loading the charge supplied through the positive power terminal to a negative polarity terminal, a second positive polarity charge loading unit loading the charge charged in the first capacitor to a negative polarity terminal, a third positive polarity charge loading unit loading the charge charged in the second capacitor, and a positive polarity charge charging/loading control unit outputting charging control signals with a same phase to the switches, and periodically or irregularly changing durations of the charging and loading control signals.