Switching Power Supply Synchronous Rectification Without Auxiliary Winding
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Solution Overview
Problem
Existing switching power-supply devices using synchronous rectification methods face challenges in managing Electromagnetic Interference (EMI) and increasing costs due to the need for auxiliary windings, which also pose safety concerns.
Innovation Solution
The integration of a charging circuit and a second control circuit in the switching power-supply device, utilizing a capacitor to charge and control an N-type transistor for rectification without an auxiliary winding, allowing for synchronous rectification at the secondary-side circuit while maintaining stable potentials and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an N-type transistor is provided between the ground-side terminal of the secondary winding and the ground-side output terminal (first configuration), then the synchronous rectification can be performed, but the ground-side terminal becomes potential floating and EMI measures become difficult
Solution Approach 1:
The patent introduces an auxiliary N-type transistor (second switching element) as an intermediary component between the ground-side terminal and ground-side output terminal. This auxiliary transistor acts as a mediator that provides a controlled path for the ground-side terminal, preventing potential floating while enabling synchronous rectification through coordinated gate control of both transistors.
2Object-affected harmful factors
If an auxiliary winding is added to drive the N-type transistor gate (second configuration), then EMI measures become easy, but the cost increases and safety is compromised
Solution Approach 1:
The patent makes the auxiliary N-type transistor serve multiple functions: it provides a stable reference potential for EMI control, enables synchronous rectification when activated, and eliminates the need for an auxiliary winding. This multi-functional approach reduces device complexity and cost while maintaining EMI performance.
Solution Approach 2:
The control circuit generates gate drive signals for both the main and auxiliary N-type transistors using internally generated clock signals and feedback, eliminating the need for external auxiliary windings. The system serves itself by using its own control resources to drive the rectification transistors.
3Object-affected harmful factors
If the ground-side terminal is kept at stable potential (second configuration), then EMI measures become easy, but an auxiliary winding must be added increasing cost
Solution Approach 1:
The auxiliary N-type transistor serves as an intermediary that provides a controlled connection path to maintain stable potential at the ground-side terminal without requiring an auxiliary winding. This mediator component enables potential stabilization while avoiding the cost and complexity of additional windings.
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 enables efficient synchronous rectification without adding auxiliary windings, reducing manufacturing costs and enhancing safety by eliminating potential winding shorts, while effectively managing EMI.
Implementation Method 1
a transformer (T) including a primary winding (T1) and a secondary winding (T3) magnetically coupled to the primary winding
Data Source
AI summary
A switching power-supply device has a smoothing capacitor connected between a ground-side output terminal connected to one end of a secondary winding of a transformer and a non-ground-side output terminal connected to the other end of the secondary winding; an N-type transistor connected between the non-ground-side output terminal and the other end of the secondary winding; a capacitor connected to a connection point of the N-type transistor and the other end of the secondary winding; a charging circuit connected between a connection point of the N-type transistor and the non-ground-side output terminal and the capacitor and configured to charge the capacitor, and a control circuit configured to perform on-and-off control of the N-type transistor by using a voltage of the capacitor.