Switching Frequency Control for Constant On-Time Voltage Converters
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Solution Overview
Problem
Existing dc-dc synchronous voltage converters controlled by constant on-time methodology face challenges in maintaining a constant switching frequency, leading to electromagnetic interference (EMI) and potential degradation of circuit performance due to varying load currents.
Innovation Solution
A switching frequency controller comprising a frequency divider, a frequency detector, an accumulation counter, and an on-time controller is used to adjust the on-time length of the switching control signal, ensuring the switching frequency remains close to the target frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If constant on-time methodology is used to control voltage converter, then transient response time is shortened and structure is simplified, but switching frequency cannot be maintained constant leading to EMI and performance degradation
Solution Approach 1:
The patent implements a feedback mechanism where the actual switching frequency is detected and compared with the target frequency, and the on-time is dynamically adjusted based on the frequency deviation. This closed-loop control ensures that while maintaining fast transient response through responsive control, the switching frequency remains stable and does not cause EMI or performance degradation.
Solution Approach 2:
The patent transitions from a static constant on-time control to a dynamic control scheme where the on-time can be adjusted in real-time based on frequency feedback. This allows the system to maintain the simplicity and fast response of constant on-time methodology while adding the capability to adapt and maintain constant switching frequency under varying conditions.
2Device complexity
If on-time is fixed in constant on-time control, then control structure is simplified, but switching frequency deviates from target frequency under varying load conditions
Solution Approach 1:
The patent changes the control parameter from a fixed constant on-time to a variable on-time that can be adjusted based on frequency deviation. The control structure monitors the switching frequency and modifies the on-time parameter dynamically to maintain the target frequency, thus improving frequency accuracy while keeping the control structure relatively simple through incremental adjustments.
3Adaptability or versatility
If switching frequency is allowed to vary with load current, then adaptability to different operating modes is improved, but electromagnetic interference and circuit performance degradation occur
Solution Approach 1:
The patent uses frequency detection and feedback control to monitor and adjust the switching frequency, ensuring it remains at the target frequency regardless of load current variations. This prevents electromagnetic interference while maintaining adaptability to different operating modes through the responsive feedback mechanism that adjusts on-time based on actual frequency measurement.
Data Source
AI summary
A switching frequency controller, a voltage converter, and a method are used for controlling switching frequency. The switching frequency controller includes a frequency divider, a frequency detector, an accumulation counter, and an on-time controller. The frequency divider generates a divisional signal having a divisional frequency according to an input signal having a target frequency. The target frequency is 2N times of the divisional frequency. The frequency detector receives the divisional frequency and a switching control signal, and calculate a number of periods that pass by during each cycle of the divisional signal. The number of periods is represented by (N+1) bits. The accumulation counter increases or decreases a control indication value by a predetermined value according to a most significant bit of the number of periods. The on-time controller adjusts an on-time length of the switching control signal according to the control indication value.