The **MF-RHT450-AP** is a high-temperature, radial-leaded PPTC (Polymeric Positive Temperature Coefficient) resettable fuse manufactured by **Bourns**. It is specifically designed for circuit protection in automotive and industrial environments where high operating temperatures are common. --- ### 1. Key Technical Specifications | Parameter | Value | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 4.50 A | Max current the device will pass without tripping at 23°C. | | **Trip Current ($I_{trip}$)** | 8.10 A | Min current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 16 V | Maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 100 A | Maximum fault current the device can safely handle. | | **Operating Temp Range** | -40°C to +125°C | Designed for extreme thermal environments. | | **Power Dissipation** | 3.6 W | Power dissipated when the device is in the tripped state. | --- ### 2. Physical Characteristics The **"AP"** suffix in the part number indicates the packaging style: * **A**: Ammo Pack (tape and reel format for automated assembly). * **P**: Lead-free/RoHS compliant. ### 3. How it Functions The MF-RHT series operates on the principle of thermal expansion: 1. **Normal Operation**: The conductive polymer is in a crystalline state, allowing current to flow with low resistance. 2. **Fault Condition**: An overcurrent or over-temperature event causes the polymer to heat up. 3. **Tripping**: Upon reaching the Curie temperature, the polymer expands and becomes amorphous, drastically increasing resistance and "opening" the circuit. 4. **Reset**: Once the fault is removed and the device cools down, the polymer shrinks, restoring the conductive paths. --- ### 4. Typical Applications Due to its high-temperature rating (125°C), this part is commonly found in: * **Automotive Electronics**: Engine control units (ECUs), motor protection, and lighting circuits. * **Industrial Controls**: Protection for sensors and actuators in hot environments. * **Medium Voltage Power Supplies**: Where ambient heat is a concern for standard fuses. --- ### 5. Part Number Breakdown | Prefix | Series | Hold Current | Packaging | | :--- | :--- | :--- | :--- | | **MF** | **RHT** | **450** | **-AP** | | Multifuse | Radial High Temp | 4.50 Amps | Ammo Pack / Lead-Free |