Flyback Controller Primary Current Sensing
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Solution Overview
Problem
Conventional flyback power conversion systems face challenges in achieving satisfactory dynamic responses and efficiency, particularly when the output load changes from no load to full load, due to the need for additional circuitry and the inefficiency caused by current sensing resistors.
Innovation Solution
A system controller is implemented with specific terminals and components to regulate power conversion systems by adjusting primary currents, charging capacitors, and detecting demagnetization processes, which includes features like sampling current sensing voltages mid-on-time to reduce errors and power dissipation, and using a large resistor during start-up to minimize power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional circuitry is added to the secondary side to achieve good output current control, then current regulation performance is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current sensing function from the secondary side and relocates it to the primary side by sensing the current through the primary winding. This eliminates the need for additional current sensing circuitry on the secondary side while maintaining current regulation capability through the controller's ability to monitor primary current and control switching accordingly.
Solution Approach 2:
The primary winding serves multiple functions: it is used for both power transfer and current sensing. By utilizing the existing primary winding for dual purposes, the patent eliminates the need for separate current sensing resistors or circuitry, thereby reducing device complexity while maintaining current regulation performance.
2Measurement precision
If a current sensing resistor is added to the secondary side to achieve output current control, then current measurement accuracy is improved, but power efficiency deteriorates due to resistive losses
Solution Approach 1:
The patent removes the current sensing resistor from the secondary side and extracts the current sensing function to the primary side. This eliminates the resistive losses associated with secondary side sensing resistors while maintaining the ability to accurately measure and control output current through primary current monitoring.
Solution Approach 2:
The controller acts as an intermediary that translates primary current information into appropriate switching control to achieve secondary current regulation. By using the controller's processing capability rather than direct secondary side sensing, the patent avoids power losses while maintaining measurement accuracy.
3Reliability
If conventional voltage regulation methods are used with auxiliary windings, then voltage regulation is achieved, but device complexity and power loss increase
Solution Approach 1:
The patent merges the voltage regulation function with the existing feedback winding, eliminating the need for separate auxiliary windings. By combining multiple regulation functions into a single winding structure, the patent reduces device complexity while maintaining effective voltage regulation capability.
Solution Approach 2:
The feedback winding serves multiple functions including voltage regulation and current sensing. By making this winding multi-functional, the patent eliminates the need for additional auxiliary windings and associated circuitry, thereby reducing device complexity while maintaining regulation performance.
4Speed
If current sensing is performed at the beginning of on-time period, then measurement speed is improved, but measurement accuracy deteriorates due to initial spike voltage
Solution Approach 1:
The patent applies preliminary blanking action by suppressing or ignoring the initial spike voltage at the beginning of the on-time period before performing voltage sampling. This preliminary suppression of harmful voltage transients allows for accurate current sensing to occur during the stable portion of the switching cycle, maintaining both speed and accuracy.
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 voltage and current regulation, improves dynamic responses, and reduces power dissipation, allowing for more efficient operation under varying load conditions.
Implementation Method 1
a primary winding (404), a secondary winding (406)... to adjust a primary current flowing through a primary winding
Implementation Method 2
charge a capacitor through the third controller terminal in response to the first signal
Data Source
AI summary
System and method for regulating a power conversion system. A system controller for regulating a power conversion system includes a first controller terminal, a second controller terminal and a third controller terminal. The system controller is configured to receive an input signal at the first controller terminal and turn on or off a switch based on at least information associated with the input signal to adjust a primary current flowing through a primary winding of the power conversion system, receive a first signal at the second controller terminal from the switch, and charge a capacitor through the third controller terminal in response to the first signal.