Isolated Switching Converter Dual-Sampling Feedback Control
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Solution Overview
Problem
Traditional isolated switching converters face inaccuracies in feedback control due to oscillation signals during rectifier startup and prolonged blanking times, which affect the sampling of output voltage, leading to inaccurate reflection of real output voltage.
Innovation Solution
The implementation of a dual-sampling circuit system, where a first sampling circuit generates an alternating current feedback signal and a second sampling circuit generates a direct current feedback signal, both based on the auxiliary winding voltage, with a compensation circuit adjusting control signals based on multiple thresholds to accurately reflect output voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a blanking time is set to avoid oscillation signals during rectifier startup, then the feedback sampling accuracy is improved, but the response time and productivity are reduced
Solution Approach 1:
The feedback sampling process is segmented into two distinct phases: AC signal sampling during rectifier conduction and DC signal sampling during rectifier off-state. This segmentation allows each sampling circuit to capture voltage information at optimal moments without interference from oscillation signals, thereby maintaining high accuracy without requiring prolonged blanking times.
Solution Approach 2:
The AC feedback signal is sampled during the rectifier conduction period before the oscillation issue occurs, and the DC feedback signal is sampled during the off-state. This preliminary action ensures that voltage information is captured at the most appropriate moments in the switching cycle, eliminating the need for extended blanking periods.
2Measurement precision
If the blanking time is extended to ensure stable sampling, then the feedback accuracy is improved, but the control response speed deteriorates
Solution Approach 1:
The feedback system dynamically switches between AC and DC sampling modes based on the rectifier conduction state. During conduction, AC sampling captures instantaneous voltage; during off-state, DC sampling provides averaged voltage information. This dynamic approach ensures accurate voltage reflection without requiring fixed extended blanking times, maintaining fast response speed.
Solution Approach 2:
The feedback sampling operates periodically in sync with the rectifier switching cycle, with AC sampling occurring during conduction phases and DC sampling during off-phases. This periodic action ensures that sampling always occurs at optimal moments, achieving high accuracy without prolonging the overall control cycle.
3Measurement precision
If dual-sampling circuits are used to improve feedback accuracy, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The auxiliary winding serves multiple functions: it provides both the AC feedback signal during rectifier conduction and the DC feedback signal during off-state. This multi-functionality eliminates the need for separate sensing windings, reducing overall circuit complexity while enabling dual-sampling for improved accuracy.
Solution Approach 2:
The first rectifier acts as an intermediary element that directs the auxiliary winding voltage to the second sampling circuit during appropriate phases. This intermediary approach enables the system to extract both AC and DC feedback signals from a single auxiliary winding without requiring complex additional circuitry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of feedback control by distinguishing between different voltage states, ensuring precise output voltage regulation and reducing electromagnetic interference, thereby improving the efficiency and reliability of isolated switching converters.
Implementation Method 1
a primary switch MP, a first sampling circuit 11, a second sampling circuit 12, a compensation circuit 14 and a feedback control circuit 15. The isolated switching converter converts an input voltage into an output voltage. The primary switch is coupled to a transformer.
Implementation Method 2
when a rectifier D1 is turned ON, a voltage Vf developed on the auxiliary winding of a transformer T1 is proportional to an output voltage Vout. So feedback information can be obtained by sensing the voltage Vf.
Implementation Method 3
The second sampling circuit is coupled to the auxiliary winding through a first rectifier, wherein the first rectifier has a positive terminal coupled to receive the voltage on the auxiliary winding and a negative terminal coupled to the second sampling circuit. The second sampling circuit is configured to generate a second feedback signal, wherein the second feedback signal comprises a direct current signal indicative of the output voltage.
Data Source
AI summary
An isolated switching converter has a primary switch and a control circuit. The control circuit has a first sampling circuit, a second sampling circuit, a compensation circuit and a feedback control circuit. The first sampling circuit is coupled to an auxiliary winding of a transformer to receive a voltage on the auxiliary winding and is configured to generate a first feedback signal having an alternating current signal indicative of an output voltage. The second sampling circuit is coupled to the auxiliary winding through a first rectifier and is configured to generate a second feedback signal having a direct current signal indicative of the output voltage. The compensation circuit is configured to generate a compensation signal based on the first feedback signal, the second feedback signal and a reference threshold. The feedback control circuit is configured to generate a primary control signal of the primary switch based on the compensation signal.