The **MF-R090-0-99** is a specific model of a **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by Bourns. These components are commonly referred to as "multifuses" or "polyfuses." --- ### 1. Technical Specifications Below are the key electrical characteristics for the MF-R090-0-99: | Parameter | Value | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.90 A | The maximum current the device can carry without tripping. | | **Trip Current ($I_{trip}$)** | 1.80 A | The minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60 V | The maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 40 A | The maximum fault current the device can safely interrupt. | | **Power Dissipation** | 0.9 W | Typical power dissipated when in the tripped state. | | **Resistance ($R_{min}/R1_{max}$)** | 0.07 – 0.22 $\Omega$ | The resistance range of the device in its initial state. | --- ### 2. Physical and Material Properties * **Package Type:** Through-hole (Radial Leaded). * **Material:** Conductive polymer mixed with carbon black. * **Terminations:** Tin-plated copper. * **Operating Temperature:** $-40^\circ\text{C}$ to $+85^\circ\text{C}$. * **Packaging Suffix (-99):** The "-99" suffix typically indicates specific bulk packaging or a standard commercial lead-free finish. --- ### 3. Functional Theory (How it Works) Unlike a traditional wire fuse that melts and must be replaced, the MF-R090 is **resettable**: 1. **Normal State:** The polymer is in a crystalline state, and carbon particles form conductive paths, allowing current to flow with low resistance. 2. **Fault State:** During an overcurrent or over-temperature event, the polymer heats up and expands into an amorphous state. This breaks the carbon chains, causing resistance to spike instantly. 3. **Reset State:** Once the power is disconnected and the device cools down, the polymer shrinks, the carbon chains reconnect, and the device returns to a low-resistance state. --- ### 4. Common Applications * **USB Port Protection:** Protecting computer peripherals from overcurrent. * **Power Supplies:** Guarding against short circuits in low-voltage transformers. * **Industrial Controls:** Protecting sensors and PLC I/O ports. * **Medical Electronics:** General circuit protection where downtime for fuse replacement is undesirable. ---