Switching Power Supply Feedback Circuit Design
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Solution Overview
Problem
Conventional switching power supplies face challenges in further reducing size and cost due to the complexity of terminal configurations and the need for additional components like drive windings and rectifying circuits.
Innovation Solution
The proposed switching power supply incorporates a regulator connected to the primary winding of a transformer, a feedback current detection circuit, and a feedback voltage generation circuit, which allows for direct feedback current supply to a photocoupler, eliminating the need for a drive winding and rectifying circuit, and enabling a three-terminal package installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional switching power supply uses a semiconductor integrated circuit with common power terminal and feedback terminal, then the number of terminals is reduced and package size is minimized, but the device complexity increases due to the need for drive winding and rectifying circuit
Solution Approach 1:
The patent extracts and eliminates the drive winding and rectifying circuit from the conventional switching power supply configuration. By using a current mirror circuit to directly generate feedback current from the error signal without requiring optical coupling through a drive winding, the complex rectifying and smoothing circuitry is removed, thereby reducing device complexity while maintaining the compact three-terminal package structure
Solution Approach 2:
The patent replaces the optical coupling mechanism (which requires drive winding and rectifying circuit) with an electrical current mirror mechanism. The current mirror circuit directly replicates the error signal current to generate feedback current, substituting the mechanical/optical system with a simpler electrical system that achieves the same feedback function without additional components
2Length of moving object
If the switching power supply uses a three-terminal package configuration, then the external shape size is reduced, but additional components like drive winding and rectifying circuit are required
Solution Approach 1:
The patent merges the feedback current generation function directly into the control circuit through the current mirror mechanism. By combining the error signal processing and feedback current generation in a single integrated circuit without separate drive winding and rectifying circuit components, the total component count is reduced while maintaining the three-terminal package configuration
Solution Approach 2:
The patent removes the drive winding and rectifying circuit components from the system. By extracting these unnecessary components and replacing their function with a current mirror circuit implemented in the integrated circuit, the component count is reduced while the compact three-terminal package structure is maintained
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 configuration results in a smaller, more cost-effective switching power supply with improved output voltage stabilization and reduced component count, achieving accurate voltage control without the need for additional circuits.
Implementation Method 1
The photo transistor 110a is optically coupled with the photo diode 110b to form a photocoupler 110
Data Source
AI summary
A switching power supply of the present invention comprises: a switching element through which a DC voltage is supplied via a primary winding; an output voltage detection circuit detecting a voltage of a secondary winding to generate an error signal; a regulator generating a predetermined voltage based on a voltage generated at a node between the switching element and the primary winding; a photocoupler through which a feedback current signal corresponding to the error signal passes; a feedback current detection circuit detecting a feedback current signal; a feedback voltage generation circuit generating a feedback voltage according to the current of the feedback current detection circuit when the switching element is OFF and holding the generated feedback voltage when the switching element is ON; and a control circuit controlling ON/OFF duty of the switching element according to an increase or decrease of the feedback voltage.