PTC Resettable Fuses
PTC Resettable Fuses (Positive Temperature Coefficient Self-Resettable Fuses) are circuit protection components based on polymer materials, which realize overcurrent protection functions through temperature-sensitive characteristics. Its core feature is “self-recovery”, that is, it can be reset without manual replacement after the fault is eliminated. It is widely used in consumer electronics, industrial equipment, and new energy fields.
1. PTC Resettable Fuses Overview
Basic Structure
PTC is composed of a polymer matrix and conductive particles. Under normal conditions, the conductive particles form a chain-like conductive path with low resistance characteristics (usually 10mΩ to 5Ω).
Protection Mechanism
When the circuit has overcurrent or abnormal temperature, the component heats up due to Joule heat, causing the polymer to expand and block the conductive path, and the resistance rises sharply to the kilo-ohm level, thereby limiting the current (the response time can be as short as 8ms). After the fault is eliminated, the material cools and shrinks, and the conductive path is automatically rebuilt.
2. What are the Core Characteristics of PTC Resettable Fuses?
Self-recovery Ability: It can be repeatedly protected tens of thousands of times, which is significantly better than traditional fusible fuses.
Fast Response: The tripping time is related to the current intensity, and the response is faster in high-current scenarios.
Low Static Power Consumption: The power consumption is extremely low under normal working conditions (such as the initial resistance of the MF-MSMD050 model is only 0.15Ω).
Wide Temperature adaptability: The operating temperature range covers -40℃ to 85℃, meeting the needs of harsh environments.
3. Technical Parameters of PTC Resettable Fuses (Typical Values)
|
Parameter |
Description |
Reference Value |
|
Holding Current (Ih) |
Maximum continuous current without triggering protection |
14mA~50A |
|
Breaking Current (It) |
Critical current for triggering high impedance state |
Depends on the model |
|
Rated Voltage |
Maximum Allowable Voltage |
15V~600V |
|
Breaking Time |
Response time from overcurrent to high impedance state |
8ms~90s |
|
Reset Time |
Time required to restore low impedance state after troubleshooting |
Seconds to minutes |
4. Where are the PTC Resettable Fuses Used?
Consumer Electronics: power adapter, USB port, LED drive circuit.
New Energy Equipment: electric vehicle battery management system, charging pile overcurrent protection.
Industrial Control: motor driver, communication equipment power module.
Battery Protection: overcharge/over-discharge protection of lithium battery pack and nickel-metal hydride battery.
5. Selection Points for PTC Resettable Fuses
1) Voltage Matching: Select a model with a rated voltage higher than the maximum operating voltage of the system.
2) Current Threshold: Determine the specification based on the normal operating current (Ih) and the maximum fault current (It).
3) Package form:
Plug-in Type (Radial/Axial Pins): Suitable for traditional PCB design.
Surface Mount Type (such as SMD package): Suitable for high-density circuit boards (such as hard disk drives and PC motherboards).
Strip Structure: Dedicated to internal integration of battery packs.
6. Common Model Examples
MF-MSMD050: Surface mount type, 15V rated voltage, 0.15Ω initial resistance, suitable for PC peripherals and POS devices.
Polyswitch Series: A brand under Tyco Electronics (TE), covering all scenarios from microelectronics to industrial equipment.
Summary
PTC Resettable Fuses have become the mainstream solution for modern circuit protection due to their self-healing characteristics and high reliability. When selecting, it is necessary to combine parameters such as voltage, current, package form, and ambient temperature to achieve precise matching.