## MF-RHT550: Electronic Specifications and Overview The **MF-RHT550** is a high-temperature, radial-leaded **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse manufactured by Bourns. It is part of the Multifuse® line, specifically engineered for automotive and industrial environments where high ambient temperatures are common. ### 1. Fundamental Component Identity | Attribute | Specification | | :--- | :--- | | **Component Type** | Resettable Fuse (PPTC) | | **Technology** | Polymer-based thermistor | | **Series** | MF-RHT (High Temperature Radial) | | **Mounting Type** | Through-hole (Radial Leads) | --- ### 2. Key Technical Specifications The "550" in the part number indicates the hold current ($I_{hold}$) rating. Below are the specific electrical characteristics: | Parameter | Value | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 5.50 Amps | The maximum current the device will pass without tripping at 23°C. | | **$I_{trip}$** | 9.80 Amps | The minimum current at which the device will switch to a high-resistance state. | | **$V_{max}$** | 16 Volts | The maximum voltage the device can withstand without damage. | | **$I_{max}$** | 100 Amps | The maximum fault current the device can safely handle. | | **$P_d$ (Typ.)** | 3.5 Watts | Power dissipated from the device when in the tripped state. | | **$R_{min}$** | 0.015 Ohms | Minimum resistance of the device in its initial state. | | **$R1_{max}$** | 0.037 Ohms | Maximum resistance measured one hour after tripping. | --- ### 3. Functional Behavior The MF-RHT550 acts as a "smart" circuit breaker. Its operation is defined by the following stages: 1. **Normal State:** The polymer contains conductive particles (carbon black) that form a low-resistance path, allowing current to flow to the load. 2. **Fault Condition:** If an overcurrent or overtemperature event occurs, the internal $I^2R$ heating causes the polymer to expand. 3. **Tripped State:** The expansion breaks the conductive chains, causing the resistance to increase exponentially. This limits the current flow to a safe leakage level. 4. **Reset:** Once the fault is removed and the device cools down, the polymer contracts, the conductive paths re-form, and the device returns to a low-resistance state. --- ### 4. Distinctive Features * **High Temperature Rating:** Unlike standard PPTCs that trip easily at 50°C-60°C, the MF-RHT series is rated for operating temperatures up to **125°C**. * **Automotive Grade:** It is **AEC-Q200 compliant**, meaning it is tested for high vibration, thermal shock, and mechanical stress. * **Fast Time-to-Trip:** Designed to react quickly to fault currents to protect sensitive downstream components like ECUs or motors. --- ### 5. Common Applications * **Automotive Electronics:** Protection for fans, power steering systems, and engine control units located in the engine bay. * **Industrial Controls:** Equipment operating in high-heat environments or near heavy machinery. * **Battery Packs:** Overcurrent protection during charging or discharging cycles.