PTC NTC Electric Blanket Heating Circuit Safety Control
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Solution Overview
Problem
Existing electric blankets are prone to electric leakage or fires due to inaccurate temperature control and aging of key elements, which can lead to short circuits or open circuits, causing local overheating and potential fires.
Innovation Solution
A safe heating circuit utilizing a Positive Temperature Coefficient (PTC) + Negative Temperature Coefficient (NTC) temperature control mode, coupled with a key element short-circuit or open-circuit detection protection circuit, allowing for precise temperature control, timely fault detection, and power supply shutdown to prevent fires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional temperature control is used in electric blankets, then the device complexity is low, but the temperature control precision is insufficient leading to safety hazards
Solution Approach 1:
The temperature control system is segmented into multiple independent detection paths: a first voltage acquisition circuit samples the voltage across the PTC heating element to detect its resistance changes, while a second voltage acquisition circuit samples the voltage across the NTC temperature sensing element. This segmentation allows precise temperature monitoring through multiple feedback channels without requiring a single complex control system.
Solution Approach 2:
The NTC element serves as an intermediary between the heating system and the controller. It provides a linear temperature-voltage relationship that is easier to process than the exponential relationship of PTC elements alone. The NTC acts as a mediator that converts temperature information into a form suitable for precise control, improving measurement precision while keeping the control logic manageable.
2Reliability
If simple temperature control is used, then the ease of manufacture is high, but the reliability is low due to aging of key elements causing short circuits or open circuits
Solution Approach 1:
The controller continuously monitors the voltages across both PTC and NTC elements during normal operation and calculates their resistance values in real-time. This preliminary monitoring detects abnormalities such as short circuits or open circuits before they lead to dangerous conditions. The system performs preliminary diagnostics by comparing measured values against expected ranges, enabling early fault detection without requiring separate dedicated detection circuits.
Solution Approach 2:
The system implements dual feedback loops: one through the PTC element monitoring circuit and another through the NTC element monitoring circuit. Both circuits provide continuous feedback to the controller about the state of the heating system. This redundant feedback mechanism ensures high reliability by cross-validating temperature and resistance measurements, allowing the system to detect faults in either element independently while maintaining manageable circuit complexity.
3Measurement precision
If PTC element alone is used for temperature control, then the device complexity is low, but the measurement precision is insufficient due to exponential resistance-temperature relationship
Solution Approach 1:
The system merges the temperature sensing functions of both PTC and NTC elements into a unified control system. The PTC element provides primary temperature control through its self-regulating properties, while the NTC element provides complementary temperature sensing with a more linear characteristic. The controller integrates information from both elements to achieve precise temperature control, combining the advantages of both material types without requiring separate independent control systems.
Solution Approach 2:
The system exploits the different resistance-temperature characteristics of PTC and NTC materials by measuring and comparing their respective resistance values. The controller adjusts operating parameters based on the combined feedback from both elements, optimizing the temperature control precision. By changing how the system utilizes electrical parameters (voltage and resistance measurements) from both elements, it achieves superior temperature sensing precision while keeping the control circuitry relatively simple through standard microcontroller processing.
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 enables precise control of heating temperatures, timely detection of faults, and automatic power shutdown, effectively preventing fires and ensuring user safety.
Implementation Method 1
a PTC electric heating element, generating heat when being electrified
Implementation Method 2
an NTC element, disposed between the PTC electric heating element and a sensing element; the sensing element, configured to receive a leakage current from the PTC electric heating element transmitted by the NTC element
Data Source
AI summary
A safe heating circuit includes a PTC electric heating element; a first switching element, coupled into a ground loop of the PTC element and configured to switch on or off a power loop of the PTC element based on an on-off control signal; a first voltage acquisition circuit, configured to sample a first temperature voltage based on a ground current of the PTC element; an NTC element, disposed between the PTC element and a sensing element; the sensing element, configured to receive a leakage current from the PTC element transmitted by the NTC element; a second voltage acquisition circuit, configured to sample a second temperature voltage based on the leakage current; and a controller, that compares the first or second temperature voltage to a set temperature voltage and output the on-off control signal based on a comparison result.