Heating device
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Solution Overview
Problem
Heating devices in automobiles face challenges in meeting stringent electromagnetic compatibility requirements, especially at high voltage levels, due to increased on-board supply voltage and pulse width modulated operations, which lead to significant electromagnetic emissions.
Innovation Solution
The heating device design separates parasitic capacitances into balanced halves by connecting heating resistors on either side of a transistor switch, ensuring opposite polarity charging and discharging, thereby canceling common mode currents and reducing radiated and conducted emissions. This is achieved by splitting the heating load into high and low sides of the transistor switch and using a symmetrically designed heating resistor assembly with an insulation layer to isolate resistive tracks from the metal sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the heating device is operated with pulse width modulated voltage at high voltage levels, then heating efficiency is improved, but electromagnetic emissions increase making it difficult to meet electromagnetic compatibility requirements
Solution Approach 1:
The heating load is divided into two equal halves (first half and second half) that are connected to opposite sides of the transistor switch. This segmentation creates two separate parasitic capacitances that can be balanced against each other, reducing the overall electromagnetic emissions while maintaining the pulse width modulated heating operation
Solution Approach 2:
The patent applies asymmetry in reverse by creating electrical symmetry through the circuit configuration. By arranging both halves of the heating load symmetrically with respect to the transistor switch and ensuring equal parasitic capacitances, the common mode currents are canceled out, reducing electromagnetic emissions
2Device complexity
If the heating load is connected directly to the transistor switch, then device complexity is reduced, but parasitic capacitances cause significant common mode currents and electromagnetic emissions
Solution Approach 1:
The heating load is segmented into two halves with equal parasitic capacitances, each connected to opposite sides of the transistor switch. This segmentation allows the parasitic capacitances to be balanced, causing the common mode currents to cancel each other out rather than adding up
Solution Approach 2:
The transistor switch acts as an intermediary element between the power supply and the heating load. By positioning the transistor switch in the center and connecting both halves of the heating load to it, the parasitic capacitances are balanced and the common mode currents are canceled, reducing electromagnetic emissions
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 approach significantly improves electromagnetic compatibility by minimizing electromagnetic emissions, ensuring compliance with stringent requirements at high voltage applications while maintaining electrical symmetry and reducing parasitic capacitance-related issues.
Implementation Method 1
Heating devices, like flow heaters, comprising a heating resistor assembly, e.g., a metallic heating plate with a resistive track
Implementation Method 2
When the transistor switch is open, parasitic capacitances between the first half of the heating load and the parasitic capacitances of the second half of the heating load are of opposite polarity so they are charged in opposite direction. When the transistor switch closes, the parasitic capacitances are discharged between them.
Data Source
AI summary
Disclosed is a heating device having a heating resistor assembly with a positive terminal, a negative terminal, and heating resistors connected in series between the positive terminal and the negative terminal, and a transistor switch connected in series with the heating resistors. A first half of the heating resistors connects the positive terminal to the transistor switch and a second half of the heating resistors connects the transistor switch to the negative terminal.