Current Detecting Circuit for Constant On-Time Power Converter
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Solution Overview
Problem
Conventional current detecting circuits in constant on-time power converters face challenges in accurately calculating the on-time of the lower bridge switch, leading to discrepancies between calculated and actual average current values.
Innovation Solution
A current detecting circuit and method that includes a time detecting circuit and a sample and hold circuit, where the time detecting circuit detects the on-time of a previous cycle's lower bridge conduction signal and the sample and hold circuit samples the inductor current at a detection time point in the next cycle, half the on-time after the rising edge of the waveform, to obtain an average current value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current detecting circuit detects current at each time point during lower bridge switch on-time and calculates average, then current measurement is performed continuously, but the calculated average current value differs from actual average current value due to valley value at last time point
Solution Approach 1:
The patent applies preliminary action by detecting the on-time of the lower bridge switch in advance during the previous cycle, then using this pre-detected on-time information to determine the exact detection time point in the next cycle. This ensures the detection occurs at the correct moment (half the on-time after rising edge) rather than at arbitrary time points, eliminating the valley value error and accurately capturing the average current value.
2Measurement precision
If current detecting circuit uses multiple detection time points to calculate average, then more data points are obtained, but calculation complexity increases and accuracy still deviates from actual average
Solution Approach 1:
The patent extracts only the essential information needed for accurate current measurement by detecting the on-time of the lower bridge switch and using it to determine a single critical detection time point. Instead of continuously sampling at multiple time points and performing complex averaging calculations, the invention extracts the on-time parameter and uses it to pinpoint the exact moment when current sampling will yield the accurate average value, thereby simplifying the circuit and calculation while maintaining or improving precision.
3Ease of operation
If detection time point is set at arbitrary moment during on-time, then detection is simplified, but the obtained current value is valley value which does not represent actual average
Solution Approach 1:
The patent employs feedback by using the detected on-time information from the previous cycle to determine the detection time point in the next cycle. The on-time detection result feeds back into the timing control mechanism, creating a closed-loop system where the detection moment is dynamically adjusted based on actual switch behavior. This feedback mechanism ensures the detection always occurs at the correct relative position (half the on-time after rising edge) regardless of variations in the switching waveform, thereby maintaining high measurement precision without complicating the detection process.
Data Source
AI summary
A current detecting circuit of a constant on-time power converter and a method thereof are provided. The current detecting circuit includes a time detecting circuit and a sample and hold circuit. A control circuit of the constant on-time power converter outputs a lower bridge conduction signal to turn on a lower bridge switch during an on-time of each cycle of the lower bridge conduction signal. The time detecting circuit detects the on-time of a cycle of the lower bridge conduction signal. The sample and hold circuit samples and holds a current of an inductor at a detection time point of a next cycle of the lower bridge conduction signal. A time between a rising edge of a waveform of the next cycle of the lower bridge conduction signal and the detection time point is equal to half the on-time.