Edge Comparator Control Circuit for Constant Switching Frequency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Buck circuits operating under Continuous Conduction Mode (CCM) in constant on-time or constant off-time control modes cannot maintain a constant switching frequency, limiting their application scope and performance.
Innovation Solution
A control method and circuit that measures the start time of a turn-on or turn-off signal and adjusts the switch's on-time or off-time to fix the frequency by reducing or increasing the switching time based on the arrival of the next signal edge, allowing for a constant switching frequency without requiring specific conditions between input and output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constant on-time or constant off-time control mode is used in CCM switching circuit, then load transient performance is improved and control structure is simplified, but switching frequency cannot be kept constant
Solution Approach 1:
The patent uses feedback by measuring the actual switching cycle duration and comparing it with the target cycle duration. The edge comparator detects whether the next switching edge arrives before or after the expected time, and the control circuit adjusts the on-time or off-time of the switch accordingly to maintain constant switching frequency while preserving excellent load transient response.
Solution Approach 2:
The control circuit dynamically adjusts the switching parameters (on-time or off-time) based on real-time feedback from the edge comparator. This dynamic adjustment allows the system to maintain constant switching frequency under varying load conditions while preserving the fast transient response characteristics of constant on-time/off-time control modes.
2Stability of the object's composition
If voltage sampling is used to control switching frequency, then frequency can be regulated, but errors are introduced due to voltage sampling delays
Solution Approach 1:
The patent replaces voltage sampling (an electrical measurement method prone to delays) with edge detection using an edge comparator. This substitution detects the actual switching edges directly without voltage sampling delays, providing more accurate timing information for frequency control while eliminating the measurement errors associated with voltage sampling.
Solution Approach 2:
The edge comparator continuously monitors and detects switching edges in advance, allowing the control circuit to predict whether the next edge will arrive early or late relative to the target cycle duration. This preliminary detection enables proactive adjustment of switching parameters before the frequency deviation occurs, improving both frequency stability and measurement accuracy.
3Device complexity
If constant on-time control mode is used, then control structure is simplified, but the method cannot be applied when specific voltage relationships are not met
Solution Approach 1:
The patent creates a universal frequency control method that can be applied to both constant on-time and constant off-time control modes, as well as to different switching circuit topologies (buck, boost, buck-boost). The edge comparator-based approach provides a unified solution that maintains constant switching frequency across various operating conditions and circuit configurations without requiring specific voltage relationships, thereby extending the application scope while keeping the control structure relatively simple.
Data Source
AI summary
A control method, a control circuit and a device for a switching circuit are disclosed, for fixing a frequency of the switching circuit when the switching circuit is operated under CCM. The present disclosure is suitable to various switching circuits, and an application scope of the control method of the switching circuit can be extended. The control method comprises: starting measuring time at a rising edge of a turn-on signal of the first switch; reducing a turn-on time or a turn-off time of the first switch when a first measured time is reached, and the rising edge in a next cycle of the turn-on signal has not arrived; increasing the turn-on time or the turn-off time of the first switch when the rising edge in the next cycle of the turn-on signal arrives but the first measured time is not reached.