变压器的复合PTC热敏电阻, 开关功率

A composite PTC thermistor is an electronic component that combines positive temperature coefficient (正温度系数) characteristics with overvoltage protection, primarily used for dual overcurrent and overvoltage protection. 复合PTC热敏电阻使用热耦合组合, 紧密拟合并封装了VDR变量和PTC热敏电阻. 它主要用于开关电源和电源表和其他电源的变压器主电路, 提供全面的电流和电压保护. This solves the difficulties associated with using a single PTC thermistor with transformers. Instruments and equipment protected by a PTC thermistor may not function properly under overvoltage or overcurrent conditions, and low-temperature instruments may not be protected by the PTC when abnormalities occur.

The following is an analysis of its core features and applications:

我. Structure and Principle

Material Composition: Typically made from a polyolefin resin, polyethylene, or epoxy resin matrix, conductive particles such as carbon black and vanadium oxide are incorporated. 室温下, the conductive particles form continuous conductive chains, resulting in low resistivity. When the temperature rises to the polymer melting point, the matrix expands, breaking the conductive chains and causing a sudden increase in resistivity (PTC effect). Composite Design: Some models integrate a PTC thermistor and a varistor (VDR) into a single package, achieving dual overcurrent and overvoltage protection through thermal coupling. 例如, during an overvoltage event, the varistor absorbs energy and generates heat, triggering a jump in the PTC’s resistance, limiting current and reducing voltage by 4%.

PTC Thermistor Application Circuit Design

二. Performance Characteristics
RISE-TO-RESISTANCE RATIO: The resistance can vary by 5-10 orders of magnitude within a narrow temperature range, making it suitable as a thermal switch element.
RESPONSIBILITY: After actuation, it takes a long time to cool down before returning to its initial state, resulting in a slow response.
SELF-RECOVERY: Automatically returns to a low-resistance state after the fault is resolved, eliminating the need for replacement.

三、. 典型的应用
Home Appliances and Industrial: Used for overcurrent protection in equipment such as electric water heaters, 电机, 和变压器.
Power Meters: Provides combined overvoltage and overcurrent protection in smart meters and switching power supplies.
汽车电子产品: Used in temperature monitoring applications such as engine control and air conditioning systems.
When a varistor absorbs large amounts of energy, 它会加热. Due to thermal coupling, the temperature of the PTC thermistor also rises. 此外, the thermistor itself heats up due to the increased current. When the temperature reaches the PTC thermistor’s switching temperature, its resistance jumps, and the current decreases sharply. 同时地, the voltage drop across the thermistor increases significantly, reducing the voltage across the varistor and allowing only a small leakage current to flow. This reduces the voltage of the protected circuit to within the normal operating voltage range, allowing the power meter to operate normally.

四号. Selection Parameters
The following parameters should be considered during selection:
Operating current (它) and non-operating current (伊赫);
Curie temperature (TC, typically 115±7°C);
Varistor voltage (V) and maximum operating voltage (最大电压).

Common models of composite thermistors