NTC thermistor doing inrush current limiting on power-up. Cold resistance is high → limits initial surge current. As it heats up from current flow, resistance drops exponentially → normal operation resumes.
Typical specs: R25°C might be 5-47Ω, drops to <1Ω at steady state. Time constant usually 5-15 seconds.
Why it matters: Prevents capacitor charging spikes from tripping breakers or damaging rectifiers in SMPS designs. Way cheaper than active PFC or soft-start circuits, but trades off efficiency (wastes ~0.5-2W as heat during operation).
Green epoxy coating is usually phenolic resin for moisture resistance. Disc form factor = higher thermal mass compared to bead types, so better surge handling but slower recovery.
Typical specs: R25°C might be 5-47Ω, drops to <1Ω at steady state. Time constant usually 5-15 seconds.
Why it matters: Prevents capacitor charging spikes from tripping breakers or damaging rectifiers in SMPS designs. Way cheaper than active PFC or soft-start circuits, but trades off efficiency (wastes ~0.5-2W as heat during operation).
Green epoxy coating is usually phenolic resin for moisture resistance. Disc form factor = higher thermal mass compared to bead types, so better surge handling but slower recovery.
