Flyback Converter Load-Transient Detection via Secondary Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Flyback converters face excessive latency in responding to load transients due to indirect and inaccurate output voltage sensing, leading to output voltage regulation issues, particularly in secondary-side regulation (SSR) converters where the detection delay causes output voltage to fall below acceptable minimums during sudden load applications.
Innovation Solution
A secondary-side controller with a sense resistor and output current detection circuit that detects load transients by monitoring the secondary-side sense resistor voltage, allowing for immediate response through increased gain in the compensation circuit and under-voltage threshold adjustments, enabling faster load transient detection and response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indirect output voltage sensing through auxiliary winding is used in PSR flyback converter, then the output voltage regulation can be achieved on primary side, but the sensing accuracy deteriorates and response time increases
Solution Approach 1:
The patent uses the auxiliary winding voltage as an intermediary to sense the output voltage on the primary side. The auxiliary winding is magnetically coupled to the transformer, allowing indirect measurement of output voltage without direct electrical connection across isolation barrier. This resolves the contradiction by providing a timing-synchronized measurement path that maintains both accuracy and fast response.
Solution Approach 2:
The patent measures the auxiliary winding voltage at the precise moment when the primary switch turns off and the secondary diode conducts. This preliminary action captures the reflected output voltage at the optimal timing point before any potential droop occurs, ensuring accurate sensing without delay while maintaining primary-side regulation capability.
2Measurement precision
If secondary-side regulation with ADC digitization is used, then output voltage regulation accuracy is improved, but detection delay increases due to ADC sampling and comparator processing
Solution Approach 1:
The patent replaces the conventional ADC digitization and software processing mechanism with an analog comparator-based detection system. The comparator directly compares the auxiliary winding voltage (proportional to output voltage) against a reference threshold and immediately generates a digital under-voltage indication. This substitution eliminates ADC sampling delays and processor overhead, achieving fast detection while maintaining regulation accuracy through proper comparator design.
3Use of energy by moving object
If output capacitor supports output voltage during light load, then power switch cycling is reduced to slow rate, but output voltage falls below minimum upon sudden load application
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the auxiliary winding voltage and compares it to a minimum threshold. When the output voltage (reflected through auxiliary winding) approaches the under-voltage threshold, the feedback immediately triggers increased power switch cycling duty cycle or frequency. This closed-loop feedback ensures the output voltage is maintained above the minimum threshold even during sudden load transients, while allowing reduced cycling during light-load conditions to minimize power consumption.
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 solution significantly reduces the detection and response time for load transients, ensuring the output voltage remains within acceptable limits without significant delay, improving both secondary-side and primary-side regulation flyback converters.
Implementation Method 1
a secondary-side sense resistor for producing a secondary-side sense resistor voltage in response to an output current
Implementation Method 2
a compensation circuit for multiplying an error signal by a gain to produce a control signal
Data Source
AI summary
A flyback converter is provided that detects a load-transient-produced increase in the output current to more quickly detect and respond to the load transient.