Auxiliary-Winding Voltage Sampling for Isolated Flyback Converters
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Solution Overview
Problem
Conventional switching power supply converters face challenges in accurately sampling the output voltage across the auxiliary winding due to high complexity and cost, especially when using optocouplers for electrical isolation, leading to errors in voltage feedback.
Innovation Solution
A method for a switching power supply converter that actively tracks the sampling position by measuring the time duration after the power switch is turned off until a preset condition is met, allowing for accurate voltage sampling with reduced complexity by using a control circuit with driving, timing, and sample-and-hold units to acquire the effective voltage sample.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional primary side sensing technique is used to indirectly detect output voltage through auxiliary winding sampling, then electrical isolation between input and output is achieved, but voltage sampling accuracy deteriorates due to errors from output rectifier voltage drop and secondary current variations
Solution Approach 1:
The patent applies dynamics by making the sampling timing adaptive rather than fixed. The control circuit dynamically adjusts the sampling moment based on real-time detection of secondary current status (when current drops to zero or near-zero). This dynamic timing adjustment ensures sampling occurs at the optimal moment when error terms are minimized, resolving the contradiction between maintaining electrical isolation and achieving high voltage sampling accuracy.
2Device complexity
If fixed time delay sampling method is used after main switch turn-off, then device complexity is reduced, but voltage sampling accuracy deteriorates under different working conditions due to varying secondary currents at sampling point
Solution Approach 1:
The patent implements feedback by having the control circuit continuously monitor the secondary current status through the auxiliary winding and use this information to determine the optimal sampling timing. The feedback loop detects when secondary current reaches zero or near-zero condition and triggers the voltage sampling at that precise moment. This feedback mechanism maintains high sampling accuracy across different working conditions without significantly increasing device complexity.
3Measurement precision
If active tracking of sampling position is implemented to minimize errors, then voltage sampling accuracy is improved, but device complexity increases due to additional control circuit requirements
Solution Approach 1:
The patent applies universality by designing the control circuit to perform multiple functions: it controls the main switch, monitors auxiliary winding voltage, detects secondary current status, determines optimal sampling timing, and executes the voltage sampling operation. By making the control circuit multi-functional rather than adding separate dedicated circuits for each function, the patent achieves high sampling accuracy through active tracking while minimizing the increase in overall device complexity.
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 enables accurate voltage sampling with reduced complexity and cost, actively tracking the sampling point to minimize errors caused by secondary side current variations.
Implementation Method 1
By magnetic coupling e of the transformer, the voltage on the auxiliary winding is proportional to the voltage on the secondary winding through the coupling between the auxiliary winding and the secondary winding
Data Source
AI summary
The invention relates to a switching power supply converter, which comprising a transformer including a primary winding and a secondary winding, a power switch circuit and a voltage input circuit, a voltage output circuit, an auxiliary winding, a control circuit, and a voltage sensing circuit; the control circuit performs that in a first turn-off period of the power switch circuit, acquiring a first time duration from a preset delay after the power switch circuit turning off until the sensed voltage corresponding to a preset condition, and acquiring a difference between the first time duration and a preset time duration as a second time duration; in a second turn-off period of the power switch circuit, acquiring the sensed voltage at the time point corresponding to the end of the second time duration starting from the preset delay after the power switch circuit turning off as an effective sample.