Flyback Converter Light-Load Efficiency via Dynamic Clamping
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Solution Overview
Problem
Flyback converters experience efficiency drops during light-load conditions due to dominant switching losses and undervoltage issues, leading to hiccup mode and inefficiencies when the load reduces to no load, as conventional green mode strategies fail to maintain supply voltage effectively.
Innovation Solution
A light-load efficiency improving apparatus for flyback converters, comprising a first detecting circuit for load detection, a second detecting circuit for supply voltage detection, and a circuit for selectively clamping the output voltage dependent signal using a bias voltage when the load is below a threshold and the supply voltage is low, preventing undervoltage lockout and optimizing switching operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If green mode is used to reduce switching loss during light-load condition, then switching loss is reduced, but supply voltage falls down to undervoltage lockout cut-off threshold value
Solution Approach 1:
The patent changes the parameter of error signal clamping voltage from a constant value to a variable value that adapts based on supply voltage levels. When supply voltage is high, a lower clamping voltage allows the converter to enter green mode and reduce switching loss. When supply voltage drops, the clamping voltage increases to prevent undervoltage lockout, thus resolving the contradiction between energy efficiency and voltage stability.
2Reliability
If power switch is forced to turn on to maintain supply voltage above threshold, then supply voltage is maintained, but switching times increase and efficiency degrades
Solution Approach 1:
The patent introduces dynamic adjustment of the error signal clamping voltage based on real-time supply voltage detection. Instead of forcing the power switch on continuously with a fixed clamping voltage, the system dynamically adapts the clamping voltage level to maintain supply voltage above the threshold only when necessary, thereby reducing unnecessary switching operations and improving efficiency while maintaining reliability.
3Productivity
If minimum VEA_CLAMP is set lower than burst_low threshold during green mode, then green mode operation is enabled, but not enough energy is available resulting in increased switching times
Solution Approach 1:
The patent implements a feedback mechanism where the supply voltage detection circuit continuously monitors the supply voltage level and adjusts the error signal clamping voltage accordingly. This feedback ensures that the clamping voltage is lowered below the burst_low threshold only when sufficient energy is available in the supply voltage, preventing increased switching times while enabling green mode operation when conditions are favorable.
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
The solution enhances light-load efficiency by maintaining supply voltage levels and reducing switching times, thereby preventing efficiency degradation and unwanted hiccup modes, ensuring stable operation even at low loads.
Implementation Method 1
a transformer 106 transforms the input voltage Vin to an output voltage Vo
Implementation Method 2
an auxiliary coil Laux of the transformer 106 provides a current Iaux to charge a capacitor C2 to produce a supply voltage Vcc
Data Source
AI summary
A flyback converter has a controller to switch a power switch so as to convert an input voltage to an output voltage for a load by monitoring an output voltage dependent signal and a current sensing signal derived from a current flowing through the power switch, a light-load efficiency improving apparatus monitors the load and a supply voltage provided for the controller to selectively clamp the output voltage dependent signal when the load is lower than a first threshold value and the supply voltage is lower than a second threshold value, so as to increase the supply voltage.