The WMF21 series thermistors are radial lead, resin-coated NTC components designed to limit inrush current in electronic systems. Key benefits - Inrush control: as temperature falls, the material constant B increases and residual resistance decreases, helping to reduce inrush current at power-on. - Efficient protection: higher heat capacity contributes to stronger, more stable current limiting. - Clear performance relation: the limiting capability is directly proportional to the product of the thermal time constant (T) and the thermal loss constant (d). - Reliable and fast: low mass combined with high performance delivers fast response, long service life and high reliability. Construction and compatibility - Radial lead resin-coated thermistors for easy inclusion in assemblies. - Suitable for the power supply loop of all types of power supplies and for ballasts/CFLs. - Also used in the heating loop of CRTs in colour TVs/monitors, as well as in heaters and heating filaments. Applications and use scenarios - Inrush current limiting in switching power supplies and supply rails to extend component life and reduce input stress. - Protection in ballast/CFL circuits where startup surge is a concern. - Heating circuit applications, including CRT heaters in colour TVs/monitors and general heating filaments, where controlled startup is required. This product emphasizes low mass, high performance, fast response, and long service life, delivering dependable inrush current limitation with high reliability.