As electronic devices become increasingly sophisticated, engineers face the critical challenge of preventing overheating to ensure stable and reliable circuit operation. PTC (Positive Temperature Coefficient) thermistors, with their unique temperature characteristics, offer an economical and efficient solution to this problem.

PTC thermistors are special semiconductor ceramic components whose resistance values show a significant positive correlation with temperature changes. At room temperature, PTC thermistors typically have low resistance values, but when the temperature exceeds their Curie temperature, the resistance increases dramatically. This unique characteristic makes PTC thermistors ideal for overheating protection applications.

Various types of PTC temperature limit sensors are available, including SMD chip types, leaded disk types, and screw-mount types, meeting nearly all overtemperature detection requirements. Additionally, specially designed motor protection sensors can be directly installed inside motor windings (stator side) to achieve precise monitoring of motor overheating.

• Overheating protection for transistor circuits
• Overheating protection for power semiconductor devices
• Overheating protection for single-phase/three-phase induction motors

PTC temperature limit sensors provide a simple yet effective solution for overheating protection in transistor circuits. Whether due to rising ambient temperatures or self-generated heat in the transistor, PTC thermistors respond promptly to prevent damage to circuit components from excessive heat.

In transistor amplifier circuits, excessive temperatures may cause transistor characteristics to degrade, affecting normal circuit operation. As shown in Figure 1, when a PTC thermistor is connected in series in a transistor circuit, its resistance increases rapidly when ambient temperature rises. This causes the transistor's base-emitter voltage to drop, thereby cutting off the transistor's load current. When ambient temperature returns to normal, the PTC thermistor's resistance returns to its lower level, and the circuit resumes normal operation.

Power semiconductor devices generate significant heat during operation. Without proper heat dissipation, these devices can easily overheat and fail. PTC temperature limit sensors effectively protect power semiconductor devices from thermal threats.

As illustrated in Figure 2, when a PTC thermistor is mounted directly on a heatsink and the heatsink temperature exceeds the set value, the thermistor's resistance increases sharply. This causes the power transistor's base voltage to drop, reducing collector current and suppressing heat generation, thereby protecting the power transistor from overheating damage.

Single-phase and three-phase induction motors are widely used in various electronic devices and industrial equipment. To prevent motor damage from overload or insufficient cooling, overcurrent and overheating protection devices are typically required. PTC thermistors serve as motor protection sensors, effectively guarding against thermal threats.

As shown in Figure 3, three motor protection sensors are mounted directly on motor windings (stator side). When the PTC thermistor temperature reaches the set value, it triggers a trip unit (circuit breaker) to cut off power, protecting the motor from overheating damage. This approach provides highly reliable motor overheating protection.

The versatility and reliability of PTC thermistors make them indispensable components in modern electronic design, offering robust protection against thermal hazards across various applications.