Switching Mode Power Supply Light Feedback Protection Circuit
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Solution Overview
Problem
Switching mode power supply apparatuses face the risk of excessive voltage being applied to the light receiving unit during abnormal situations, such as short circuits, which can destroy insulation and potentially harm users.
Innovation Solution
Incorporating a disconnection unit that includes a Zener diode and a fusible element, which disconnects power to the light receiving unit when the voltage exceeds a predetermined threshold, preventing excessive voltage from being applied and protecting the user.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light receiving unit is directly connected to the feedback terminal without voltage protection, then the voltage detection function is simple and reliable, but excessive voltage during abnormal situations can destroy insulation and harm users
Solution Approach 1:
A disconnection unit comprising a Zener diode and fusible element is introduced as an intermediary component between the light receiving unit and the feedback terminal. The Zener diode acts as a voltage threshold detector, and the fusible element serves as a protective mediator that disconnects the circuit when excessive voltage is detected, preventing direct transmission of harmful voltage to the light receiving unit while maintaining normal voltage detection functionality
Solution Approach 2:
The disconnection unit is pre-configured with a Zener diode set to a specific breakdown voltage (e.g., 250V) and a fusible element with predetermined current-carrying capacity. Before any abnormal voltage occurs, these components are already in place to automatically activate when the threshold is exceeded, disconnecting the light receiving unit from excessive voltage before insulation destruction can occur
2Object-affected harmful factors
If a disconnection unit with Zener diode and fusible element is added to protect against excessive voltage, then user safety and insulation protection are improved, but the device complexity and cost increase
Solution Approach 1:
The fusible element is designed as a disposable protective component that is intentionally made relatively inexpensive. When excessive voltage causes it to melt and disconnect the circuit, it serves its protective purpose and is replaced. This approach prioritizes user safety while accepting the cost of periodic component replacement, making the overall system economically viable despite the added complexity
Solution Approach 2:
The Zener diode is selected with specific electrical parameters (breakdown voltage, power rating) tailored to the operating conditions. By carefully choosing these parameters, the disconnection unit provides precise protection at the threshold where it is needed most, optimizing the balance between protection capability and component cost
3Productivity
If the MOSFET and switching controller are integrated in a single device, then the power supply apparatus becomes more compact and efficient, but the risk of short circuit and excessive voltage to the light receiving unit increases
Solution Approach 1:
The disconnection unit serves as a protective intermediary that specifically addresses the insulation vulnerability created by integration. The Zener diode and fusible element form a dedicated protection circuit between the feedback terminal and light receiving unit, isolating the light receiving unit from voltage spikes that may occur due to internal short circuits in the integrated MOSFET-switching controller device
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
The solution effectively prevents insulation destruction and user injury by ensuring the light receiving unit is disconnected from excessive voltages, demonstrated by withstanding voltages up to 3000 V without insulation damage, compared to 500 V in existing systems.
Implementation Method 1
a Zener diode through which a current flows if the voltage of the power applied to the light receiving unit exceeds the predetermined threshold value
Implementation Method 2
a fusible element that is opened by the current flowing through the Zener diode
Data Source
AI summary
A switching mode power supply apparatus includes a conversion unit to convert input power into output power having a predetermined voltage by performing a switching operation, a light emitting unit to emit light if the voltage of the output power exceeds a predetermined threshold voltage, a light receiving unit to receive the light emitted from the light emitting unit and output a signal indicative of the voltage of the output power, a switching controller to control the switching operation of the conversion unit according to the voltage of the output power indicated by the signal output from the light receiving unit, and a disconnection unit to disconnect power applied to the light receiving unit if a voltage of the power applied to the light receiving unit exceeds a predetermined trigger voltage.