## Technical Overview: MF-R090 (PTC Resettable Fuse) The **MF-R090** is a popular electronic component belonging to the **Multifuse®** product line manufactured by **Bourns**. It is a polymer-based **Positive Temperature Coefficient (PTC)** resettable fuse, commonly used for overcurrent protection. --- ### 1. Key Technical Specifications The following table summarizes the primary electrical characteristics of the MF-R090: | Parameter | Value | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 0.90 A | Maximum current at which the device will not trip (at 23°C). | | **$I_{trip}$** | 1.80 A | Minimum current at which the device will always trip. | | **$V_{max}$** | 60 V | Maximum voltage the device can withstand without damage. | | **$I_{max}$** | 40 A | Maximum fault current the device can safely interrupt. | | **$P_d$ (typ.)** | 0.91 W | Power dissipated from the device when in tripped state. | | **$R_{min}$ / $R_{max}$** | 0.07 / 0.12 $\Omega$ | Resistance range of the component before tripping. | --- ### 2. Physical and Design Features * **Package Type:** Radial Leaded (Through-hole). * **Material:** Conductive polymer combined with carbon black. * **Safety Standards:** Usually UL, CSA, and TUV recognized. * **Visual ID:** Typically a circular, coated disc (often yellow or brown) with "R090" printed on it. --- ### 3. How It Works The MF-R090 operates on the principle of thermal expansion: 1. **Normal State:** In standard operation, the carbon particles form conductive paths, allowing current to flow with low resistance. 2. **Overcurrent Event:** When current exceeds the threshold ($I_{trip}$), the polymer heats up and expands. 3. **Tripped State:** The expansion breaks the chain of carbon particles, causing the resistance to increase exponentially. This "chokes" the current to a safe leakage level. 4. **Resetting:** Once the fault is removed and the power is cycled/disconnected, the device cools down, the polymer contracts, and the conductive paths are restored. --- ### 4. Common Applications * **Power Supplies:** Protection against short circuits in AC/DC adapters. * **Industrial Controls:** Protecting PLCs and sensor interfaces. * **Computing:** USB port protection and motherboard peripherals. * **General Electronics:** Any circuit requiring 0.9A continuous current where manual fuse replacement is inconvenient.