## Overview of MF-R075/90 The **MF-R075/90** is a specific model of **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by Bourns. It is part of the MF-R series, commonly referred to as "MultiFuses." These components are used to protect electronic circuits from overcurrent and short-circuit conditions. --- ### 1. Key Technical Specifications The part number itself contains encoded information about its performance. Here are the primary electrical characteristics for the MF-R075/90: | Parameter | Value | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 0.75 A | The maximum current the device will hold without tripping at 23°C. | | **$I_{trip}$** | 1.50 A | The minimum current at which the device is guaranteed to trip. | | **$V_{max}$** | 90 V | The maximum voltage the device can withstand without damage. | | **$I_{max}$** | 40 A | The maximum fault current the device can safely interrupt. | | **$P_d$ (typ.)** | 0.9 W | Power dissipated from the device when in a tripped state. | | **Resistance ($R_{min}/R1_{max}$)** | 0.25 – 0.70 $\Omega$ | The initial resistance range of the device at 23°C. | --- ### 2. Physical Characteristics The MF-R075/90 is a **radial-leaded** component, meaning it is designed for Through-Hole Technology (THT) on printed circuit boards (PCBs). * **Material:** Cured, flame-retardant epoxy polymer (meets UL 94V-0). * **Lead Wire:** Tin-plated copper. * **Marking:** Usually marked with the Bourns logo, "R075", and a date code. --- ### 3. Functional Principle Unlike a traditional fuse that blows and must be replaced, the PPTC "resets" itself: 1. **Normal State:** The polymer contains conductive particles (carbon black) that form a low-resistance path. 2. **Overcurrent Event:** Excessive current causes $I^2R$ heating. As the temperature reaches the polymer's phase change point, the polymer expands. 3. **Tripped State:** The expansion breaks the conductive paths, increasing resistance by several orders of magnitude, effectively cutting off the current. 4. **Reset:** Once the fault is removed and the device cools down, the polymer contracts, the paths reconnect, and the fuse returns to a low-resistance state. --- ### 4. Applications The 90V rating of this specific model makes it suitable for higher voltage applications than standard 16V or 30V PPTCs: * **Telecommunications:** Protection for line cards and customer premise equipment. * **Industrial Controls:** Protection for sensors and actuators. * **Power Supplies:** Secondary protection for transformers and DC power ports. * **Security Systems:** Protection for alarm panels and motion sensors. ---