Switching Power Supply Synchronous Rectifier Oscillation Control
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Solution Overview
Problem
Switching power supply devices with synchronous rectifier circuits can experience self-excited oscillation when the main switching element is turned OFF, leading to potential voltage increases that may exceed component withstand voltages, causing damage and inefficiencies.
Innovation Solution
A switching power supply device with a cascade forward configuration and a self-excited synchronous rectifier circuit, featuring an auxiliary switch circuit that detects and prevents self-excited oscillation by turning off the commutation switch when a voltage exists at the output terminal, using a configuration with a main transformer, main switch, rectifying switch, commutation switch, and auxiliary switch circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a synchronous rectifier circuit with self-excited configuration is used, then circuit complexity is reduced and mounting space is decreased, but self-excited oscillation occurs when main switch is turned OFF causing voltage to exceed component withstand voltages
Solution Approach 1:
The patent applies preliminary anti-action by introducing a control circuit that detects the OFF state of the main switch and proactively prevents self-excited oscillation before it can damage components. The control circuit monitors the switching state and blocks the oscillation pathway by controlling the commutation switch, thereby preventing the harmful voltage buildup that would otherwise exceed component withstand voltages.
Solution Approach 2:
The patent uses an intermediary control circuit as a mediator between the main switch and the synchronous rectifier circuit. This control circuit includes detection means to sense the main switch state and control means to regulate the commutation switch, thereby mediating the energy flow and preventing uncontrolled oscillation while maintaining the benefits of the self-excited configuration.
2Reliability
If a separately-excited configuration is used to drive synchronous rectifier, then reliability is improved with direct signal transmission, but device complexity increases and mounting space increases
Solution Approach 1:
The patent applies universality by making the control circuit serve multiple functions: it detects the main switch state, generates appropriate control signals, and regulates the commutation switch all within a single integrated circuit. This multi-functional approach eliminates the need for separate excitation circuits while maintaining reliable signal transmission and oscillation prevention.
Solution Approach 2:
The control circuit performs self-service by autonomously detecting the switching state and generating the necessary control signals without requiring external separately-excited circuitry. The circuit uses its own resources to monitor and control the synchronous rectifier, thereby reducing overall device complexity while maintaining reliable operation.
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
Prevents continuation of self-excited oscillation without affecting normal operation, ensuring the commutation switch remains OFF and preventing electric current draw, thus protecting components and maintaining efficiency.
Implementation Method 1
a main transformer that has a primary-side main winding and a secondary-side main winding
Implementation Method 2
a rectifying switch that is connected to the secondary-side main winding in series to form a rectifying switch series circuit and that is turned ON in synchronization with a turning ON state of the main switch; and a commutation switch that is connected to the rectifying switch series circuit in parallel and that is turned ON in synchronization with a turning OFF state of the main switch
Data Source
AI summary
A switching power supply device includes: a main transformer; a main switch that is connected between a high potential terminal of an input direct current voltage source and a primary-side main winding; a synchronous rectifier circuit includes: a rectifying switch that is connected to a secondary-side main winding in series and that is turned ON in synchronization with a turning ON state of the main switch and a commutation switch that is connected to the rectifying switch series circuit in parallel and that is turned ON in synchronization with a turning OFF state of the main switch; and an auxiliary switch circuit that turns the commutation switch OFF. When the main switch stops a switching operation while a voltage exists at a first output terminal on a high potential side, the auxiliary switch circuit turns the commutation switch OFF to prevent continuation of self-excited oscillation.