TFT-LCD Switching Power Supply EMI Reduction via Dynamic Frequency
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Solution Overview
Problem
TFT-LCD circuits face significant issues with electromagnetic interference (EMI) radiation and conduction problems due to the fixed switching frequency in switching power supplies, leading to inefficiencies in power board isolation.
Innovation Solution
A switching power supply design incorporating a pulse width modulation (PWM) controller, electronic signal generator, and field effect transistor (FET), where voltage signals with varying frequencies are used to periodically change the switching signal frequency, reducing EMI radiation and conduction issues by preventing the use of a single switching frequency for extended periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed switching frequency is used in the switching power supply, then the circuit design is simple and easy to implement, but the electromagnetic interference (EMI) radiation increases and conduction problems occur
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The PWM controller dynamically adjusts the switching frequency based on feedback signals, allowing the system to adapt to different operating conditions and reduce EMI radiation while maintaining stable power conversion.
Solution Approach 2:
The patent implements periodic action through the use of frequency modulation where the switching frequency varies periodically according to the feedback signal. This periodic variation in frequency prevents continuous operation at a single frequency, thereby reducing cumulative EMI radiation and conduction issues.
2Stability of the object's composition
If a fixed switching frequency is used in the switching power supply, then the power conversion is stable, but the conduction influence increases when power board isolation is insufficient
Solution Approach 1:
The system maintains stability through dynamic frequency adjustment rather than fixed frequency. The feedback mechanism ensures that while the frequency varies, the power conversion remains stable by continuously adapting to load conditions and maintaining proper isolation.
Solution Approach 2:
The patent changes the frequency parameter dynamically based on operating conditions. By varying the switching frequency according to feedback, the system reduces conduction influence while maintaining stable power conversion, avoiding the problems associated with fixed frequency operation.
3Object-affected harmful factors
If the switching frequency is reduced to lower EMI, then the conduction problems improve, but the power conversion efficiency decreases
Solution Approach 1:
The system uses periodic frequency modulation to alternate between different switching frequencies. This allows the system to operate at higher frequencies when efficiency is critical and at lower frequencies when EMI reduction is prioritized, optimizing both performance and interference reduction.
Solution Approach 2:
The patent dynamically changes the frequency parameter based on real-time conditions. When EMI levels are high, the frequency is reduced; when efficiency is paramount, the frequency is increased. This adaptive parameter change optimizes both EMI reduction and power conversion efficiency.
Data Source
AI summary
The present disclosure relates to a TFT-LCD and the driving circuit and the switching power supply thereof. The switching power supply includes a PWM controller, an electronic signal generator, and a field effect transistor. The output pins of the electronic signal generator being configured to output voltage signals that vary periodically between multiple voltage ranges. The frequency selection pins of the PWM controller and the output pins of the electronic signal generator are connected to receive the voltage signals from the electronic signal generator, and the PWM controller outputs switching signals of a predetermined frequency through at least one output pin according to a voltage range of the voltage signals received by the frequency selection pins. A gate pin of the FET connects to output pins of the PWM controller, and a source pin of the FET is grounded.