Cot Converter Frequency Control via Variable On-Time
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Constant-on-time (COT) converters experience increased switching frequency with load increases, leading to higher power loss due to quicker output voltage decreases, which results in inefficiency.
Innovation Solution
A switching mode power supply (SMPS) with an on-time generator and pulse width modulation (PWM) generator that adjusts the on-time period based on load levels, maintaining switching frequency within a predetermined range by extending the on-time period as load increases, thereby reducing power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switch is turned off quickly after the predetermined time period to maintain fast response to load changes, then the output voltage regulation speed is improved, but the switching frequency increases leading to higher power loss
Solution Approach 1:
The patent applies dynamics by making the on-time period variable rather than fixed. The on-time generator dynamically adjusts the on-time period based on the detected output voltage level and load conditions. When output voltage drops quickly (indicating heavy load), the on-time period is extended to prevent excessive frequency increase. When output voltage is stable (light load), the on-time period returns to the predetermined value for fast response. This dynamic adjustment resolves the contradiction between fast regulation speed and power loss.
Solution Approach 2:
The patent changes the parameter of on-time period based on operating conditions. The control circuit monitors output voltage and adjusts the on-time period parameter accordingly - extending it when voltage drops quickly to limit frequency increase, and reducing it when voltage is stable to maintain fast response. This parameter change strategy directly addresses the contradiction by adapting the timing parameter to balance regulation speed and power loss.
2Loss of energy
If the on-time period is extended to reduce switching frequency and power loss, then energy efficiency is improved, but the response time to load changes increases
Solution Approach 1:
The system dynamically adjusts the on-time period based on real-time load detection. When a load increase is detected (output voltage drops quickly), the on-time period is extended only for that specific cycle to handle the transient condition, then returns to the shorter predetermined period. This dynamic behavior allows the system to reduce power loss during heavy load while maintaining fast response during light load conditions, effectively resolving the time-loss versus energy-loss contradiction.
Solution Approach 2:
The control circuit changes the on-time period parameter adaptively - extending it when voltage drop rate indicates heavy load to reduce switching frequency and power loss, and maintaining it at the predetermined shorter value when voltage is stable to ensure fast response. This conditional parameter change resolves the contradiction by applying different timing parameters for different operating conditions.
3Measurement precision
If the switching frequency is allowed to increase with load to maintain output voltage regulation, then voltage control accuracy is improved, but power loss increases
Solution Approach 1:
The patent uses dynamic on-time adjustment to decouple voltage control accuracy from switching frequency. The control circuit maintains accurate voltage regulation by detecting output voltage level and adjusting on-time accordingly, but limits the resulting switching frequency by extending on-time only when necessary for voltage recovery, not proportionally with load. This dynamic control achieves voltage accuracy without the direct frequency-load relationship that causes power loss.
Solution Approach 2:
The system changes the on-time period parameter based on voltage feedback rather than load feedback. By monitoring output voltage and adjusting on-time to maintain voltage within tolerance, the system achieves voltage control accuracy. However, it limits power loss by not allowing on-time (and thus frequency) to increase proportionally with load - instead, on-time is extended only enough to recover voltage, then returns to baseline.
Data Source
AI summary
A SMPS having a switch; an output port coupled to a load, configured to provide a voltage feedback signal and a current feedback signal; an on-time generator, having an input end coupled to the current feedback signal, and having an output end providing a time signal indicating a time period; and a PWM generator, having a first input end coupled to the voltage feedback signal, a second input end coupled to the time signal, and an output end providing a PWM signal that is coupled to the control end of the switch, and wherein the PWM signal is configured to turn ON the switch when the voltage feedback signal is lower than a threshold voltage, and the PWM signal is configured to turn OFF the switch after the time period.