The **MF-RX110/72** is a specific model of a **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by Bourns. It is designed to protect electrical circuits from overcurrent and short-circuit conditions. --- ### 1. Key Technical Specifications The following table summarizes the primary electrical characteristics of the MF-RX110/72: | Parameter | Value | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 1.10 Amps | The maximum current the device will carry without tripping. | | **$I_{trip}$** | 2.20 Amps | The minimum current at which the device will switch to high resistance. | | **$V_{max}$** | 72 Volts | The maximum voltage the device can withstand without damage. | | **$I_{max}$** | 40 Amps | The maximum fault current the device can safely handle. | | **$P_d$ (typ)** | 1.50 Watts | Power dissipated from the device when in a tripped state. | | **$R_{min}$** | 0.150 $\Omega$ | Minimum resistance of the device at 23°C. | | **$R_{1max}$** | 0.380 $\Omega$ | Maximum resistance measured one hour after tripping. | --- ### 2. Physical Construction and Package * **Series:** MF-RX/72 (High voltage radial leaded series). * **Material:** Conductive polymer mixed with carbon black. * **Form Factor:** Radial leaded (Through-hole mounting). * **Dimensions:** Typically circular or rectangular "disk" shape with two metal leads. * **Coating:** Flame retardant epoxy polymer (meets UL 94V-0 requirements). --- ### 3. How it Works (The PTC Effect) The MF-RX110/72 functions differently than a standard one-time fuse: 1. **Normal Operation:** At normal currents, the polymer is in a crystalline state with carbon chains forming conductive paths, resulting in low resistance. 2. **Fault Condition:** When an overcurrent occurs, the device heats up ($I^2R$ heating). 3. **Tripping:** Once the temperature reaches a critical point, the polymer expands into an amorphous state, breaking the carbon chains. The resistance increases exponentially. 4. **Resetting:** Once the fault is removed and the power is cycled (allowing the device to cool), the polymer shrinks, re-establishing the conductive paths. --- ### 4. Typical Applications Because of its 72V rating, this part is commonly used in: * **Security Systems:** Protecting sensors and control panels. * **Industrial Controls:** Overcurrent protection for motors and transformers. * **Power Supplies:** Secondary side protection. * **Telecommunications:** Protection against power cross and lightning surges. ---