A PTC thermistor is a type of resistor whose resistance increases as temperature rises. It is widely used in applications such as temperature sensing and current limiting in circuits. Murata's POSISTOR® PTC thermistors are made from high-quality ceramic materials, offering excellent reliability and performance. The product line includes various package types—such as surface mount and leaded designs—as well as components tailored for different functions like overcurrent protection, overheat protection, and surge current suppression. This article highlights the three key characteristics of the POSISTOR® series. 1. Resistance-Temperature Characteristics Despite minor variations between normal operating temperature and the Curie point, POSISTOR® maintains a nearly constant resistance-temperature relationship. Its behavior is characterized by a sharp increase in resistance once the temperature exceeds the Curie point (CP). The Curie point is defined as the temperature at which the resistance value doubles compared to its value at 25°C. 2. Current-Voltage Characteristics (Static Characteristics) This refers to the relationship between the applied voltage and the regulated current when the internal heat generated by the PTC thermistor balances with the external heat dissipation. The curve shows both a peak current point and a section of constant power output. 3. Current-Time Characteristics (Dynamic Characteristics) This describes how the current changes over time before thermal equilibrium is reached. It is marked by an initial high current that rapidly decreases. Technical Terminology Protection Current The maximum current level is referred to as the "protection threshold current" on the voltage-current characteristic curve. When the current through the POSISTOR® is below this threshold, it operates as a normal fixed resistor, stabilizing at the intersection point A between the load curve and the PTC curve. However, if the current exceeds the threshold, the stable point shifts to intersection B. Protection Threshold Current Range The range of the protection threshold current depends on factors like ambient temperature, resistance value, temperature characteristics, and physical design. As shown in Figure 7, within the temperature range of -10°C to +60°C, the maximum trip current and minimum non-operating current define the operational limits. If the current is below the non-operating current, the POSISTOR® acts as a standard resistor. Once the current exceeds the trip current, it activates to protect the circuit from overload. Operating Time The operating time is the period between applying voltage and the current dropping to a lower level. Traditionally, it is measured as the time required for the inrush current to decrease to half its initial value (I₀/2). Capacitive Panel PC,Capacitive Screen Panel PC,Capacitive Touch PC Shenzhen Innovative Cloud Computer Co., Ltd. , https://www.xcypc.com
The three most important characteristics of PTC thermistors
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