Induction Heating Circuit for E-Cigarettes With Lower Switch Voltage
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Solution Overview
Problem
Conventional electromagnetic induction heating apparatuses for electronic cigarettes, particularly those using class-E power amplifiers, face challenges with high drain-to-source peak voltage requirements, leading to increased costs and manufacturing difficulties, and have a low power utilization factor, making them inefficient for applications with limited voltage and current sources.
Innovation Solution
The apparatus employs a current mode class-D power amplifier with a pair of transistor switches and a parallel-structured LC resonant network, allowing for adaptive control of the heating temperature by adjusting the operating frequency and using a driving unit to estimate resistance changes in the heat-generating body, thereby optimizing power transfer and reducing manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a class-E power amplifier is used for electromagnetic induction heating, then the heating speed is rapid and the apparatus size is small, but the drain-to-source peak voltage becomes very high, increasing manufacturing difficulty and cost
Solution Approach 1:
The patent changes the operating parameters by using a class-D power amplifier instead of class-E, and operates the parallel LC resonant network at a frequency lower than its resonant frequency. This parameter change reduces the peak voltage stress on switches while maintaining rapid heating capability through controlled impedance matching and power transfer optimization.
Solution Approach 2:
The patent employs dynamic frequency control where the operating frequency of the power amplifier is adjusted relative to the resonant frequency of the LC network. By dynamically operating below resonance and adapting the driving frequency, the system achieves rapid heating while controlling peak voltage through dynamic impedance management rather than fixed high-voltage operation.
2Volume of stationary object
If a class-E power amplifier is used for electromagnetic induction heating, then the apparatus size is small, but the power utilization factor is very low, making it inefficient for applications with limited power sources
Solution Approach 1:
The patent changes the power amplifier class from E to D and operates the LC network off-resonance at a lower frequency. This parameter change fundamentally improves power utilization by enabling better impedance matching between the amplifier and load, reducing energy loss while maintaining compact apparatus size through efficient power transfer at optimized operating points.
Solution Approach 2:
The patent utilizes periodic switching action in the class-D power amplifier with controlled duty cycles and frequency modulation. By applying periodic drive signals at frequencies below the LC resonant frequency, the system achieves efficient energy transfer through controlled on-off cycles, improving power utilization while maintaining small apparatus dimensions.
3Productivity
If the operating frequency is increased to improve heating efficiency, then the heating speed increases, but the peak voltage and current requirements increase, making it unsuitable for limited power sources
Solution Approach 1:
The patent employs dynamic frequency control where the operating frequency is kept below the resonant frequency of the LC network. This dynamic operating strategy allows the system to achieve high heating efficiency through controlled power transfer at lower frequencies, avoiding the peak voltage and current requirements that would result from operating at or above resonance with limited power sources.
Solution Approach 2:
The patent implements adaptive frequency control where the operating frequency is adjusted based on the heating requirements and power source limitations. By using feedback mechanisms to monitor and adjust the driving frequency relative to the LC resonant frequency, the system optimizes heating efficiency while maintaining peak voltage and current levels within the capabilities of limited power sources.
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 significantly enhances the power utilization factor, reduces manufacturing costs, and allows for efficient heating of electronic cigarette aerosol-forming articles, even with limited power sources, by minimizing peak voltages and currents, and enabling adaptive temperature control.
Implementation Method 1
an AC magnetic field is generated in an LC-type resonant network including an inductor to raise the temperature of the metal heat-generating body
Implementation Method 2
there is an electromagnetic inductive heating method using heat generation characteristics corresponding to power loss by generating eddy currents
Implementation Method 3
a parallel-structured LC resonant network comprising a resonant inductor connected to an output terminal of the switch unit and electromagnetically inductively coupled with an inductor component of a heat-generating body and a resonant capacitor connected in parallel to the resonant inductor
Data Source
AI summary
An electromagnetic induction heating apparatus for heating an aerosol-forming article of an electronic cigarette includes: a power supply unit configured to supply DC power; a power amplifier including a switch unit comprising a pair of transistor switches having a differential structure and receiving DC power from the power supply unit, and a parallel-structured LC resonant network including a resonant inductor connected to an output terminal of the switch unit and electromagnetically inductively coupled with an inductor component of a heat-generating body for heating the aerosol-forming article of the electronic cigarette, and a resonant capacitor connected in parallel to the resonant inductor; and a driving unit configured to adjust a temperature of the heat-generating body by adjusting an operating frequency of the switch unit of the power amplifier to control an amount of current of the resonant inductor electromagnetically inductively coupled with the inductor component of the heat-generating body.