SMPS Overvoltage Cutoff Detection Circuit
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Solution Overview
Problem
Switching-mode power supplies (SMPS) for image forming apparatuses face damage and liability issues due to overvoltage conditions, as they are not equipped with effective mechanisms to cut off or manage voltages higher than their rated voltage, leading to potential circuit damage and product failure.
Innovation Solution
The SMPS incorporates a rectifying circuit unit, a transformer, a main switch, a first overvoltage detecting unit, and a switching control unit to detect and manage overvoltage conditions by stopping the switching operation or cutting off the input AC voltage, utilizing Zener diodes for reference voltage determination and a PWM IC for control, ensuring the output voltage remains within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an SMPS is designed without overvoltage detection and cutoff mechanisms, then the device complexity is reduced and manufacturing cost is lowered, but the reliability of the SMPS deteriorates when overvoltage conditions occur
Solution Approach 1:
The patent implements preliminary overvoltage detection before the overvoltage can damage the SMPS circuits. The detection unit continuously monitors the input voltage and triggers the cutoff mechanism in advance, preventing harmful effects before they occur. This aligns with the principle of performing required action in advance to prevent future problems.
Solution Approach 2:
The patent introduces an intermediary overvoltage detection and control circuit between the power input and the SMPS main circuit. This intermediary unit detects overvoltage conditions and activates the cutoff switch to isolate the harmful voltage from the vulnerable circuits, serving as a protective mediator that prevents direct damage.
2Reliability
If an overvoltage cutoff mechanism is added to the SMPS, then the reliability and protection against damage are improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The overvoltage detection unit is designed to automatically detect abnormal voltage conditions and trigger the cutoff mechanism without requiring external intervention or complex control systems. The circuit serves itself by monitoring its own input conditions and activating protection when needed, reducing the need for additional complex control architecture.
Solution Approach 2:
The patent monitors voltage parameter changes in the input power supply. When the voltage exceeds a predetermined threshold, the detection unit responds by changing the circuit state through the cutoff switch, transitioning from a conducting state to a blocked state. This parameter-based control simplifies the protection mechanism compared to complex multi-sensor systems.
3Object-affected harmful factors
If a low-voltage varistor is used to blow a fuse during overvoltage, then product liability is avoided, but the SMPS and image forming apparatus suffer circuit damage
Solution Approach 1:
The patent implements preliminary overvoltage detection that triggers the cutoff mechanism before the voltage level becomes high enough to blow the fuse and cause circuit damage. By detecting and responding to overvoltage conditions earlier in the process, the system prevents the harmful sequence of fuse blowing and circuit damage while still protecting against product liability.
Solution Approach 2:
The patent converts the potentially harmful overvoltage condition into a detectable signal that triggers a protective response. By treating the overvoltage as a detectable parameter rather than an immediate threat, the system transforms what would be a destructive event into an opportunity for early intervention and protection.
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 solution effectively prevents damage to the SMPS and image forming apparatus by detecting and managing overvoltage conditions, ensuring the output voltage remains within the rated voltage range, thereby minimizing product liability and maintaining operational stability.
Implementation Method 1
a rectifying circuit unit to rectify an alternating-current (AC) voltage input from an external power supply source into a direct-current (DC) voltage
Implementation Method 2
a transformer to transform the rectified DC voltage input to a primary coil and outputs the transformed DC voltage to a secondary coil
Implementation Method 3
utilizing Zener diodes for reference voltage determination
Data Source
AI summary
A switching-mode power supply (SMPS) for an image forming apparatus which may prevent an overvoltage supplied to the SMPS, and damage to circuits in the SMPS in the image forming apparatus. The SMPS includes a rectifying circuit to rectify an alternating-current (AC) voltage input from an external power supply source into a direct-current (DC) voltage, a transformer to transform the rectified DC voltage input to a primary coil and output the transformed DC voltage to a secondary coil, a main switch that is connected to the primary coil and switches an output of the transformer, a first overvoltage detecting unit to determine whether the rectified DC voltage is an overvoltage by comparing the rectified DC voltage with a first reference voltage, and a switching control unit to control a switching operation of the main switch based on a result of the determination.