Circuit & System Protection


Resettable fuses for telecom line protection

2 November 2005 Circuit & System Protection

Wickmann offers an extensive line of resettable and blow-type overcurrent protectors for telecommunications and networking equipment. The new radial-leaded Polymer Polyfuse HVR250 and HVR600 Series are optimised to provide overcurrent protection for applications that must pass Telcordia GR-1089, UL 60950, and EIA-IS-968 (formerly FCC Pt.68) requirements.

The HVR250 and HVR600 Series are designed to withstand a maximum of 250 V a.c. and 600 V a.c. Power Cross condition and to operate continuously at up to 60 V d.c. The devices are available in sorted resistance ranges, narrow resistance bin variances, and pre-tripped for better line balance performance and further noise reduction. The HVR250 Series is offered from 80 mA through 180 mA and HVR600 Series is offered with 150 mA and 160 mA hold currents.

The Polymer Polyfuse is actually a positive polymeric temperature coefficient (PPTC) device consisting of conductive carbon black particles. Under normal operating conditions, strings of carbon particles conduct current while exhibiting a very low internal resistance. When trip or fault current is exceeded, the particle strings break up and disburse randomly, which raises the internal component resistance by several orders of magnitude. This rapid increase in resistance limits current flow to nearly zero, effectively protecting the downstream circuitry. When the fault subsides or power is removed, the Polyfuse cools and resets its state.



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