The **MF-RHT200** is a specific model of a **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by Bourns. It is part of the MF-RHT series, which is engineered for high-temperature environments. --- ## 1. Technical Specifications The "200" in the model name typically indicates the hold current. Below are the primary electronic characteristics: | Parameter | Specification | | :--- | :--- | | **Hold Current ($I_{hold}$)** | 2.0 Amperes | | **Trip Current ($I_{trip}$)** | 3.8 Amperes | | **Max Voltage ($V_{max}$)** | 16 Volts | | **Max Current ($I_{max}$)** | 100 Amperes | | **Operating Temperature** | -40 °C to +125 °C | | **Power Dissipation** | 1.4 Watts (Typical) | --- ## 2. Key Features * **Resettable Protection:** Unlike standard thermal fuses that blow and must be replaced, the PPTC resets itself once the fault (overcurrent) is removed and the device cools down. * **High Temperature Rating:** The "HT" designation stands for **High Temperature**. While standard PPTCs trip prematurely at high ambient temperatures, this series is rated up to **125 °C**, making it ideal for automotive or industrial engine compartments. * **Radial Leaded Package:** It features a through-hole design with two leads, usually coated in a flame-retardant epoxy polymer. --- ## 3. How it Works (Electronic Principle) The MF-RHT200 functions based on the physical properties of its conductive polymer composite: 1. **Normal State:** At normal currents, the conductive particles inside the polymer form low-resistance chains, allowing electricity to flow easily. 2. **Fault State:** If an overcurrent occurs, the $I^2R$ heating causes the polymer to expand. 3. **Tripping:** As the polymer expands, the conductive chains break apart. The resistance increases exponentially (often by several orders of magnitude), effectively "opening" the circuit. 4. **Resetting:** Once power is removed and the heat dissipates, the polymer shrinks, the chains reconnect, and the device returns to a low-resistance state. --- ## 4. Typical Applications * **Automotive Electronics:** Protection for motors, actuators, and electronic control units (ECUs) located near the engine. * **Industrial Controls:** Power supplies and sensors in high-heat environments. * **Medium Voltage DC:** General overcurrent protection for circuits up to 16V.