SMPS Controller Switching Between CCM and DCM via Average Current
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Solution Overview
Problem
Switched mode power supplies face challenges in efficiently transitioning between continuous conduction mode (CCM) and discontinuous conduction mode (DCM) without direct measurement of inductor current, which affects energy efficiency and battery charging processes.
Innovation Solution
A controller with an average current comparator and switch signal generation circuit that determines and switches between CCM and DCM based on average current thresholds, predicting inductor current zero crossings to optimize switching patterns and prevent negative currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of inductor current is used to transition between CCM and DCM, then mode transition accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses an intermediary approach by measuring the voltage across the switch instead of directly measuring the inductor current. The switch voltage waveform contains embedded information about the inductor current status (continuous or discontinuous conduction mode), allowing the controller to determine the appropriate operating mode without requiring direct current sensing circuits.
2Loss of energy
If DCM is used near the end of battery charging, then energy efficiency is improved, but control complexity increases
Solution Approach 1:
The patent implements dynamic switching between CCM and DCM based on real-time operating conditions. The controller dynamically adjusts the switching pattern by detecting whether the inductor current reaches zero during the off-time, allowing the system to transition between continuous and discontinuous conduction modes to optimize efficiency while managing control complexity through adaptive rather than static control.
3Device complexity
If switch voltage measurement is used to determine conduction mode, then device complexity is reduced, but measurement precision may be insufficient
Solution Approach 1:
The patent employs feedback by continuously monitoring the switch voltage waveform and using this information to determine conduction mode. The controller uses the measured switch voltage to infer inductor current behavior, creating a feedback loop that allows accurate mode detection without complex direct current measurement circuits.
Data Source
AI summary
In accordance with an embodiment, a controller for a switched mode power supply includes an average current comparator that determines whether an average current within the switched mode power supply is below a current threshold, and a switch signal generation circuit coupled to the average current comparator having switch signal outputs configured to be coupled to a switching circuit of the switched mode power supply. The switch signal generation circuit produces a first switching pattern in a first mode of operation and produces a second switching pattern a second mode of operation. When the average current comparator determines that the average current is below the current threshold, the switch signal generation circuit is operated in a first mode, and when the average current comparator determines that the average current is not below the current threshold, the switch signal generation circuit is operated in a second mode.