6 note: circuit diagrams shown for example only. for more detailed product information and data sheets or to discuss your specific requirements please contact welwyn components ltd. welwyn components ltd. have over 60 years experience in designing and manufacturing resistive components. telephone lines can be subjected to a large range of voltage disturbances, many of which can damage switching equipment. this has led to the need for circuit protection against both high voltage transients, usually of short duration due to lightning strikes and overloads of longer duration caused by accidental direct connection to mains power lines. these two faults are separated into primary and secondary protection. primary protection handles the high voltage transients, and is usually located within the exchange. secondary protection is usually built into the equipment to be protected, and deals with both current and voltage limiting. voltage limiting prevents damage to the equipment and shock hazards, and current limiting prevents damage to wiring and voltage limiters. a typical application circuit is shown right where the resistors are designed for ring signal sending through a solid state relay. the resistors are protected from lightning surge by over-voltage protection in the system and the resistors are required to withstand pulse of 15 watts for 1 second and 75 watts for 0.1 second, repeated 60 times. 4. telecommunications for this application, welwyn has developed the pulse withstanding chip (pwc series) described below. for full details on this product, see our application note "pulse withstanding chip resistors". welwyn components limited welwyn electronics park, bedlington northumberland ne22 7aa, uk telephone: +44 (0) 1670 822181 facsimile: +44 (0) 1670 829465 email: info@welwyn-tt.com website: www.welwyn-tt.com irc inc. (afd) 4222 south staples street corpus christi, texas 78411, usa telephone: +1 361 992 7900 facsimile: +1 361 992 3377 email: ircafd@irctt.com website: www.irctt.com excellence in technology general note welwyn components reserves the right to make changes in product specification without notice or liability. all information is subject to welwyn s own data and is considered accurate at time of going to print. ?welwyn components limited resistive components excellent pulse handling performance thick film technology provides wide resistance and temperature ranges (1ohm to 10 meg ohm; -55 to +155?) standard and custom chip sizes (0805 to 2512) size 0805 1206 2010 2512 power @70? 0.125w 0.33w 0.75w 1.5w resistance range 1r0 to 10m tolerance 0.5, 1, 2, 5% lev 150v 200v 400v 500v tcr <10r:200ppm/? 10r:100ppm/? operating temperature -55 to +155? values e96 preferred other values to special order pulse capability see following pages issue a ?05.04 subsidiaries of tt electronics plc electrical data pulse withstanding chip resistors pwc series circuit-protection_an_a.qxd 5/11/04 9:39 am page 2
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