Switch-Mode Converter Control Circuit for Inductor Current Detection
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Solution Overview
Problem
In switch-type converters, high switching frequencies and large duty cycles can result in inaccurate control due to difficulties in detecting inductor current during the on time of the second switch, leading to oscillations and limited minimum on time for the second switch, especially when the on time is less than the current detection blanking time.
Innovation Solution
A control circuit that includes a current detection circuit to monitor inductor current thresholds and a logic circuit to deactivate the first switch and activate the second switch during a regulation time, using PWM and zero-crossing detection signals, ensuring accurate control by extending the regulation time beyond the current detection blanking time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency is increased and the duty cycle is increased, then the power conversion efficiency is improved, but the inductor current detection accuracy deteriorates due to the on time being less than the current detection blanking time
Solution Approach 1:
The control circuit proactively extends the second switch on-time to ensure it exceeds the current detection blanking time before detection is attempted. This preliminary timing adjustment guarantees that the current detection circuit can accurately measure the inductor current at the appropriate moment, preventing detection failures that would occur with high-frequency switching and large duty cycles
2Speed
If the current detection blanking time is reduced to enable detection during high frequency operation, then the switching frequency is improved, but the control stability deteriorates leading to oscillations
Solution Approach 1:
The control circuit dynamically adjusts the second switch on-time based on the relationship between switching frequency, duty cycle, and current detection blanking time. By making the timing parameters adaptive rather than fixed, the circuit maintains stable operation across varying conditions without requiring reduction of the blanking time, thus preventing oscillations while supporting high-frequency operation
3Measurement precision
If the second switch on-time is extended beyond the current detection blanking time, then the inductor current detection accuracy is improved, but the minimum on-time requirement limits the switching frequency
Solution Approach 1:
The control circuit changes the timing parameters by extending the second switch on-time to be greater than the current detection blanking time. This parameter adjustment ensures accurate current detection while the overall switching frequency is maintained through coordinated control of both switch timing, effectively decoupling the detection timing requirement from the switching frequency limitation
Data Source
AI summary
A control circuit configured to control a power stage circuit of a switch-type converter can include: a current detection circuit configured to detect whether an inductor current rises to a first threshold value during an on time of a first switch, and to detect whether the inductor current is greater than a second threshold value when an on time of a second switch is greater than or equal to a current detection blanking time, where the power stage circuit includes the first and second switches and the inductor; and a logic circuit configured to deactivate a first switch control signal and to activate a second switch control signal when the inductor current rises to the first threshold value such that the first switch remains off and the second switch remains on during a regulation time.