WMF21 series thermistors are designed to limit inrush current in power supply circuits, including switching power supplies, UPS systems, CFLs, electronic ballasts, and CRT heater/filament circuits. These radial-lead, resin-coated thermistors feature a compact size, high power handling, effective inrush current suppression, fast response time, and high reliability. Performance characteristics include a negative temperature coefficient (NTC), where resistance decreases as temperature increases. Inrush current limiting capability is enhanced by higher thermal capacity, which is directly proportional to the product of the thermal time constant (τ) and thermal dissipation constant (δ). Common applications include switching power supplies, uninterruptible power supplies (UPS), compact fluorescent lamps (CFL), electronic ballasts, and general power supply circuits. Color: Black. Material: Metal. Package includes: 1 thermistor. Note: Screen settings and lighting conditions may cause slight color variation between the image and the actual product. Dimensional tolerances: ±1–3 cm.