Induction Heating Power Limiting Circuit for Voltage Variations
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Solution Overview
Problem
Existing induction heating systems for electrophotographic image forming apparatuses face challenges in preventing excessive temperature rises due to variations in input voltage, leading to inadequate power supply when required, especially when the CPU malfunctions, and current limiting methods are costly and complex.
Innovation Solution
An induction heating apparatus with a power limiting unit that includes first and second limiting circuits, tailored to different input voltage ranges, to control high-frequency current supply based on detected voltage and current, ensuring appropriate power limiting without overloading the system, even when the CPU is malfunctioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single input current limit value is used for all input voltage ranges, then the circuit configuration is simple, but the power supply becomes inadequate when input voltage varies
Solution Approach 1:
The patent divides the input voltage range into multiple regions (first input voltage range and second input voltage range) and provides separate input current limit values for each region. This segmentation allows the circuit to adapt to different input voltage conditions without requiring complex real-time calculation, resolving the contradiction between adaptability and complexity.
2Reliability
If input current limit value is expressed as a secondary function of input voltage detection value, then power limiting is achieved, but the circuit configuration becomes complex and costly
Solution Approach 1:
The patent pre-calculates and stores input current limit values corresponding to different input voltage ranges in a lookup table or predetermined data structure. During operation, the circuit simply retrieves the appropriate limit value based on the detected voltage range, avoiding complex real-time calculations and reducing circuit complexity while maintaining reliable power limiting.
3Reliability
If CPU control is used for power regulation, then temperature control is achieved, but the system becomes vulnerable to CPU malfunction
Solution Approach 1:
The patent implements a dedicated power limiting circuit that operates independently of the CPU control. The circuit automatically monitors input current and voltage, compares them against predetermined limit values, and regulates power supply without requiring CPU intervention. This self-service approach eliminates the vulnerability to CPU malfunction while maintaining simple control logic.
4Productivity
If input current limit value varies with input voltage, then appropriate power supply is achieved, but the control becomes complex
Solution Approach 1:
The patent changes the control parameter from a single fixed current limit to multiple predetermined current limit values corresponding to different input voltage ranges. The circuit switches between these parameter sets based on the detected voltage level, achieving appropriate power supply efficiency across different conditions without implementing complex continuous adjustment mechanisms.
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 excessive temperature rises and ensures consistent power supply across varying input voltages, maintaining safety and efficiency while simplifying the circuit configuration, even when the CPU is out of control.
Implementation Method 1
When the high-frequency current is caused to flow through the coil L, an eddy current is induced on a surface of the conductive heating element FB by a generated AC magnetic field
Implementation Method 2
an eddy current is induced on a surface of the conductive heating element FB by a generated AC magnetic field so that Joule heat is generated
Data Source
AI summary
An induction heating apparatus includes a current supply unit configured to supply a high-frequency current to a coil for inductively heating a conductive heating element based on a direct current obtained by rectifying AC power supplied from an AC power supply, a driving unit configured to output a drive pulse for supplying the high-frequency current from the current supply unit, a control unit configured to control a frequency of a drive pulse output by the driving unit, and a power limiting unit configured to limit an operation of the driving unit when input power determined based on an input voltage of the AC power supply and an input current to the current supply unit exceeds a predetermined value.