Boost Converter PFM Switching Frequency Control for LED Backlight Noise Reduction
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Solution Overview
Problem
Power converting devices in computing devices generate audible noise and electromagnetic interference (EMI) when operating in low power modes, negatively impacting user experience by affecting subsystems and reducing power efficiency in display devices.
Innovation Solution
A boost converter that switches between pulse width modulation (PWM) and pulse frequency modulation (PFM) modes based on load thresholds, maintaining a switching frequency above an audible frequency threshold to minimize noise and EMI, using a logic circuit to monitor current and voltage limits and adjust pulse output accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power converting devices operate in low power modes to improve energy efficiency, then power efficiency is improved, but audible noise and electromagnetic interference increase
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable rather than fixed. The controller dynamically changes the switching frequency based on operating conditions, specifically increasing it when in audio frequency range to reduce audible noise while maintaining power efficiency benefits of low power modes.
Solution Approach 2:
The patent changes the switching frequency parameter to resolve the contradiction. By monitoring when the switching frequency falls within the audio frequency range and automatically increasing it, the system eliminates audible noise and EMI while continuing to operate in power-saving modes.
2Object-generated harmful factors
If switching frequency is increased above audible frequency threshold to reduce audible noise, then audible noise is reduced, but power consumption increases
Solution Approach 1:
The system dynamically adjusts switching frequency only when necessary (when detected to be in audio frequency range) rather than maintaining a constantly high frequency. This selective adjustment reduces audible noise while minimizing the impact on power consumption by returning to lower frequencies when safe to do so.
Solution Approach 2:
The controller periodically monitors the switching frequency and makes adjustments as needed. This periodic action allows the system to maintain low power consumption during normal operation while temporarily increasing frequency only when audible noise becomes an issue, rather than continuously operating at high frequency.
3Power
If PWM mode is used for high load operation to maintain performance, then power output is improved, but audible noise may occur when load decreases
Solution Approach 1:
The system dynamically switches between PWM and PFM modes based on load conditions. During high load operation, PWM provides full power output. When load decreases and switching frequency enters the audio range, the system transitions to PFM mode and adjusts frequency to eliminate audible noise while maintaining adequate power output for the reduced load.
Solution Approach 2:
The power converting device incorporates multiple operating modes (PWM and PFM) within a single controller, allowing it to universally handle different operating conditions. This multi-functionality enables the system to optimize for power output during high load while eliminating audible noise during low load, rather than being limited to a single mode.
Data Source
AI summary
This application relates to systems, methods, and apparatus for controlling a switching frequency of a boost or flyback converter to be above an audible frequency range when operating the boost or flyback converter in a pulse frequency modulation (PFM) mode. The boost or flyback converter uses one or more switches for converting power for a display panel. In order to boost the switching frequency when operating in the PFM mode, the boost or flyback converter can selectively implement certain current and/or voltage limits for pulses that are generated as a result of the switching. The current and/or voltage limits can be set according to a load of the boost or flyback converter, and a correspondence between the current and/or voltage limits and the loads can be stored in a lookup table accessible to the boost or flyback converter.