Synchronous Rectifier Gain Tuning via Integrator Error Detection
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Solution Overview
Problem
Existing synchronous rectifier systems face challenges in maintaining transconductance matching between the transformer secondary winding voltage and output voltage, leading to inefficiencies and potential system failures due to mismatched gain, which is difficult to monitor and adjust over the component's lifetime.
Innovation Solution
A method and circuit for gain tuning in synchronous rectifiers that integrates voltage across the transformer secondary winding, detects body diode conduction, and adjusts channel gain based on integration errors to match transconductance, using an integrator, comparator, and digital circuit to perform autotuning and minimize gain mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external resistor ladder is used for transconductance matching, then transconductance matching is improved, but device complexity and manufacturing cost increase due to additional pins and external components
Solution Approach 1:
The patent extracts the transconductance matching function from external components (resistor ladder) and implements it within the integrated SR controller using an internal resistor divider network. This eliminates the need for external tuning components and additional pins, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The output voltage sensing pin is designed to serve multiple functions: it is used for both output voltage sensing and transconductance matching detection. The same pin and circuitry are utilized for different purposes, eliminating the need for separate external components and reducing device complexity while maintaining matching precision.
2Measurement precision
If external tuning is required for transconductance matching, then transconductance matching is improved, but productivity decreases due to increased test time and resistor trimming requirements
Solution Approach 1:
The system performs self-testing and self-adjustment of transconductance matching through integrated circuitry that automatically detects and compensates for mismatches without requiring external trimming components or manual adjustment during manufacturing testing.
Solution Approach 2:
The transconductance matching is built into the controller design from the beginning, with internal resistor dividers pre-configured to provide the necessary voltage division ratios. This preliminary integration eliminates the need for post-manufacturing trimming and reduces test time.
3Measurement precision
If resistor trimming is performed to eliminate process mismatch, then transconductance matching is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent changes the approach from trimming discrete external resistors to using integrated resistor dividers with fixed, precisely-controlled resistance ratios manufactured directly in the semiconductor fabrication process. This parameter change eliminates the need for time-consuming post-manufacturing trimming operations.
4Ease of operation
If fixed transconductance matching is implemented, then initial operation is improved, but reliability decreases over SR lifetime due to component degradation and mismatch
Solution Approach 1:
The patent implements continuous feedback monitoring of the output voltage through the integrated sensing circuitry. The controller continuously compares the divided output voltage against the expected demagnetization timing, detecting any drift caused by component degradation and adjusting the SR turn-off timing accordingly to maintain optimal operation throughout the SR lifetime.
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 ensures stable and efficient operation by automatically tuning transconductance at power-up, maintaining Volt-second balancing across a range of external resistor values, reducing power loss and output ripple, and enhancing system reliability by continuously monitoring and adjusting for gain mismatch.
Implementation Method 1
integrating a voltage across the secondary side winding of the transformer
Implementation Method 2
detecting when a body diode of the synchronous rectifier begins to conduct current
Data Source
AI summary
A synchronous rectifier includes: an integrator configured to integrate a voltage across a secondary side winding of a transformer over an integral period having an expected zero integral value; a first comparator configured to detect an end of a demagnetization phase of the secondary side winding based on diode detection; and a digital circuit configured to adjust a channel gain of the synchronous rectifier based on an integration error at the end of the integral period, the integration error corresponding to the difference between the integrated voltage at the end of the integral period and the expected zero integral. Corresponding methods of gain tuning and a power converter are also described.