SMPS Adaptive COT Control for Frequency Stability
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Solution Overview
Problem
Constant ON time (COT) control in switching mode power supplies (SMPS) leads to large variations in switching frequency with input and output voltage variations, causing interference and increased switching loss, necessitating improved control methods to stabilize the system.
Innovation Solution
A SMPS with a controller that generates a switching control signal based on input and output voltages, using a ramp signal and reference signal to regulate ON time, allowing both switching frequency and inductor ripple current to vary with input and output voltages, thereby optimizing system stability and reducing switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If constant ON time control is used to achieve quick transient response, then transient response speed is improved, but switching frequency varies greatly with input and output voltage changes
Solution Approach 1:
The patent applies dynamics by making the ON time variable instead of fixed. The ON time control circuit adjusts the ON time duration based on real-time feedback from the output voltage, allowing the system to adapt to changing load conditions while maintaining stable switching frequency. This dynamic adjustment resolves the contradiction by enabling both quick transient response and frequency stability.
Solution Approach 2:
The patent implements feedback through an output regulation circuit that continuously monitors the output voltage and feeds this information back to the ON time control circuit. This closed-loop feedback mechanism allows the system to automatically adjust the ON time to maintain stable switching frequency while responding quickly to transient changes in load or input voltage.
2Loss of energy
If switching frequency is limited to minimize switching loss, then energy efficiency is improved, but interference to the rest of the system increases
Solution Approach 1:
The patent changes the parameter of switching frequency from a fixed value to a dynamically adjustable parameter. By varying the switching frequency within an optimized range based on operating conditions, the system minimizes switching loss while avoiding frequency ranges that cause interference. This is achieved through the ON time control circuit that adjusts the duty cycle to keep switching frequency within optimal bounds.
3Device complexity
If ON time is fixed for simple control, then device complexity is reduced, but inductor ripple current varies greatly with voltage changes
Solution Approach 1:
The patent applies dynamics by transitioning from fixed ON time to variable ON time control. The ON time control circuit dynamically adjusts the ON time duration based on feedback signals, which stabilizes the inductor ripple current across varying voltage and load conditions. This dynamic approach maintains relatively simple circuitry while achieving stable ripple current.
Data Source
AI summary
A SMPS has a switching circuit and a controller. The switching circuit has an input terminal and an output terminal, and also includes a switch and an inductor, wherein the switching circuit regulates an output voltage at the output terminal based on an input voltage at the input terminal by controlling a switching action of the switch. The controller generates a switching control signal to control the switch, where the switching control signal transits from a first state to a second state when an output signal at the output terminal satisfies a predetermined condition, and the switching control signal transits from the second state to the first state after a period of time. And a switching frequency of the switch and an inductor ripple current of the inductor both vary with the input voltage.