Auto-Selectable Frequency Locking Buck Converter
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Solution Overview
Problem
Conventional buck converters experience inefficiency at light loads due to switching loss and variable switching frequency, which complicates EMI filter design and reduces power efficiency.
Innovation Solution
An auto-selectable frequency locking buck converter with a frequency locking unit that adjusts the switching frequency based on load conditions by modifying the resistance value of an RC network, ensuring constant switching frequency across different load sections, thereby improving efficiency and simplifying EMI filter design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the buck converter uses current mode hysteretic control with variable switching frequency, then power efficiency is improved at light loads, but EMI filter design becomes difficult and switching frequency stability deteriorates
Solution Approach 1:
The patent implements a dynamic frequency locking mechanism that automatically adjusts the switching frequency based on load conditions. The frequency locking unit compares the actual switching frequency with a reference frequency and dynamically adjusts the PWM duty cycle to maintain a locked frequency at full load while allowing variable frequency at light loads, thus resolving the contradiction between efficiency and EMI filter design complexity
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on load conditions. At full load, the frequency is locked to a predetermined value to simplify EMI filter design. At light loads, the frequency varies to maintain high efficiency by reducing switching losses. This parameter change strategy resolves the technical contradiction
2Device complexity
If the switching frequency is locked to a constant value, then EMI filter design is simplified, but power efficiency at light loads deteriorates due to increased switching loss
Solution Approach 1:
The patent segments the operating range into two regions: full load region where frequency locking is applied to simplify EMI filter design, and light load region where variable frequency operation maintains efficiency. The frequency locking unit selectively activates based on load detection, applying frequency locking only when necessary for EMI compliance while allowing efficiency-optimized variable operation at light loads
Solution Approach 2:
The system dynamically switches between frequency locking mode and variable frequency mode based on load conditions. At full load, frequency locking is enabled to simplify EMI filter design. At light loads, the locking is released to allow frequency variation that reduces switching losses, thus resolving the contradiction
3Loss of energy
If the switching frequency varies with load, then power efficiency is maintained across load ranges, but frequency stability and EMI compliance deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the frequency locking unit continuously monitors the switching frequency and compares it with a reference frequency. When the frequency deviates from the reference (at full load), the feedback loop adjusts the PWM duty cycle to restore the locked frequency, thus maintaining frequency stability and EMI compliance while preserving the ability to vary frequency for efficiency at light loads
Solution Approach 2:
The patent changes the frequency control strategy based on load parameters. At full load, the frequency parameter is locked to a stable reference value to ensure EMI compliance. At light loads, the frequency parameter is allowed to change dynamically to maintain efficiency. This conditional parameter change resolves the contradiction between efficiency and stability
Data Source
AI summary
A current mode hysteretic buck converter employing an auto-selectable frequency locking circuit is disclosed. The auto-selectable frequency locking type buck converter include a current mode hysteretic buck converter for converting an input DC voltage into a lower DC voltage, and a frequency locking unit for locking a switching frequency of the current mode hysteretic buck converter wherein the switching frequency is locked through adjusting a locking value of the switching frequency to be a predetermined value according to a size of a load. The buck converter is, based on the current mode hysteretic control, related to a circuit that locks the switching frequency of the converter to reduce the difficulty of designing electromagnetic interference (EMI) filters in the converter. In addition, the buck converter can improve the efficiency at light load by adjusting the switching frequency which is locked according to the load current.