Isolated Switching Circuit Output Current Control
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Solution Overview
Problem
Switching regulators, particularly flyback converters, face challenges in accurately controlling output current due to variations in input voltage and load uncertainty, exacerbated by the isolating barrier that complicates control and introduces propagation delays in feedback loops.
Innovation Solution
A method and system for controlling output current in switching circuitry with an electrically isolated input and output circuit, where the switching element is controlled based on input voltage, input current, and reflected output voltage to maintain a constant output current level, operating in boundary conduction mode, continuous conduction mode, or discontinuous conduction mode, without direct measurement of output current or voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an opto-coupler is used to relay control information through the isolating barrier, then electrical isolation between input and output circuits is achieved, but propagation delay in the feedback loop increases reducing system dynamics and accuracy
Solution Approach 1:
The patent extracts the opto-coupler from the feedback loop and replaces it with a direct electrical connection through the isolating barrier. The reflected output voltage is obtained directly at the input circuit terminal without passing through an opto-coupler, eliminating the propagation delay while maintaining electrical isolation through the transformer's magnetic coupling.
Solution Approach 2:
The patent uses the transformer's magnetic field as an intermediary to transfer control information. The reflected output voltage appears directly at the primary side terminal through magnetic coupling, serving as a mediator that provides both electrical isolation and instantaneous feedback without the delays inherent in opto-coupler-based isolation methods.
2Measurement precision
If the output current is controlled based on direct measurement of output current and voltage, then control accuracy is improved, but the complexity of the control circuit increases due to the isolating barrier
Solution Approach 1:
The patent uses the reflected output voltage as an intermediary parameter that provides indirect measurement of output conditions. This voltage, obtained directly at the input circuit terminal through magnetic coupling, serves as a mediator that enables accurate control of output current without requiring direct measurement circuits on the output side, thus simplifying the overall control circuit complexity.
Solution Approach 2:
The transformer provides self-service by automatically generating the reflected output voltage signal that contains the necessary information for control. This eliminates the need for additional sensing circuits, amplifiers, and isolation components that would otherwise be required to achieve accurate output current control in isolated switching regulators.
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 effectively stabilizes output current despite input voltage and load changes, reducing variations and maintaining a consistent current level, thus enhancing control accuracy and system dynamics.
Implementation Method 1
a transformer having a primary winding and a secondary winding
Data Source
Figure 1~2
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Figure 6~7
AI summary
System and methodology for controlling output current of switching circuitry having an input circuit and an output circuit electrically isolated from each other. A value of the output current may be determined based on input voltage, input current and reflected output voltage representing the voltage in the input circuit which corresponds to the output voltage. A switching element in the input circuit is controlled to produce the determined value of output current.