This study presents a low-cost, practical approach for determining the average trip current level from a statistically significant sample of polymer positive temperature coefficient (PPTC) fuses. The experimental method uses a controlled constant-current source (CCS) to test PPTC fuses over a range of standard room temperatures without an expensive temperature chamber. This novel approach enables designs to practically investigate the reliability of trip current levels for equivalent specified PPTC fuses from different manufacturers. The experimental setup uses a calibrated CCS circuit to incrementally increase current through a PPTC fuse by 0.01 A. The current flow duration for each applied CCS setting was set to the specified time-to-trip value before device trip determination. The trip condition is identified when the sensed PPTC current drops to 50% of the specified fault trip current. To prevent thermal runaway, an empirically determined zero-current cool-down period separates each current increment. Testing revealed differences in the average trip currents of PPTC fuse samples from different manufacturers: 1.26 A, 1.10 A, and 1.06 A, respectively. The determined 95% confidence interval trip-current ranges also revealed a significant difference between PPTC manufacturer populations. The findings reveal that PPTC determined average trip current within the standard room-temperature range can serve as an effective comparison metric between manufacturers with equivalent device specifications.
Niekerk et al. (Wed,) studied this question.
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