Constant On-Time Control for Buck-Boost Converters
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Solution Overview
Problem
Traditional buck-boost converters experience significant power loss and complex logic for determining working modes, leading to abrupt mode transitions and output voltage spikes.
Innovation Solution
A novel constant on-time control scheme is implemented, which senses output voltage and inductor current to generate feedback and compensation signals, comparing them to control the switching of transistors and manage on-time thresholds for smooth mode transitions, thereby reducing power loss and eliminating output voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional fixed frequency peak current control scheme is used in BUCK or BOOST mode, then power loss is reduced, but mode transition logic becomes complicated and output voltage spikes occur
Solution Approach 1:
The patent changes the control parameter from fixed frequency to variable frequency constant on-time control. By maintaining a constant on-time for the main switch regardless of operating mode, the system automatically adapts between BUCK and BOOST modes without complex transition logic, while still achieving reduced power loss through optimized switching characteristics
Solution Approach 2:
The constant on-time control scheme serves multiple functions simultaneously: it controls both BUCK and BOOST modes with the same control mechanism, handles mode transitions automatically, and eliminates the need for separate control logic for different operating conditions, thereby simplifying the overall system complexity
2Loss of energy
If traditional fixed frequency peak current control scheme is used, then power loss is reduced, but output voltage stability deteriorates during mode transitions
Solution Approach 1:
By changing from fixed frequency to constant on-time control, the switching frequency automatically adjusts based on the load and input voltage conditions. This dynamic parameter adjustment ensures smooth mode transitions without abrupt changes in output voltage, maintaining stability while still achieving reduced power loss through optimized duty cycles
Data Source
AI summary
A control method used in a four-switch buck-boost converter includes: sensing the output voltage and generating a feedback signal; generating a compensation signal based on a reference signal and the feedback signal; sensing the current flowing through the inductor and generating a current sensing signal; comparing the current sensing signal with the compensation signal; turning on the first and third transistors and turning off the second and fourth transistors when the current sensing signal reduces to be lower than the compensation signal; turning off the first transistor and turning on the second transistor when the on-time of the first transistor in one switching period reaches a first time threshold; and turning off the third transistor and turning on the fourth transistor when the on-time of the third transistor reaches a second time threshold.