Positive Temperature Coefficient devices (PTCs) 2017 by Littelfuse

More catalogs by Littelfuse | Positive Temperature Coefficient devices (PTCs) 2017 | 128 pages | 2017-11-12


Page 4 of Positive Temperature Coefficient devices (PTCs) 2017

poly-fuse® resettable ptcs ptc characteristics and terms continued leakage current when a ptc is in a tripped state it protects the circuitry by limiting the current flow to a low leakage level leakage current can range from less than a hundred milliamps ma at rated voltage up to a few hundred milliamps ma at lower voltages fuses on the other hand completely interrupt the current flow when tripped and this open circuit results in no leakage current when subjected to an overload current time-current characteristic comparing the timecurrent curves of ptcs to time-current curves of fuses show that the speed of response for a ptc is similar to the time delay of a littelfuse slo-blo® fuse interrupting rating ptcs are rated for a maximum ambient temperature effects are in addition to the normal rerating ptcs hold and trip rating must be rerated when applied at conditions other than room ambient for example any rise in ambient temperature will decrease the hold current rating as well as the trip current a reduction in ambient temperature will increase the trip current as well as the hold current short circuit current at rated voltage also known as breaking capacity or imax this fault current level is the maximum current that the device can withstand safely keeping in mind that the ptc will not actually interrupt the current flow see leakage current above a typical littelfuse ptc short circuit rating is 40a or for the battery strap ptcs this value can reach 100a fuses do in fact interrupt the current flow in response to the overload and the range of interrupting ratings vary from tens of amperes a up to 10,000 a amperes at rated voltage temperature rerating the useful upper limit for a ptc is generally 85ºc while the maximum operating temperature for fuses is 125ºc the temperature rerating curves in the table below compare ptcs to fuses and illustrate that more rerating is required for a ptc at a given temperature temperature rerating curves comparing ptcs to fuses chart key littelfuse ptcs are not rated above 60v while fuses are rated up to 600v curve a thin-film fuses and 313 series 010 to .150a hold current rating the hold operating current rating for ptcs can be up to 14a while the maximum level for fuses can exceed 30a curve b flat-pak® nano2® pico® blade terminal special purpose and other leaded and cartridge fuses except 313.010 – .150a resistance reviewing product specifications indicates that similarly rated ptcs have about twice sometimes more the resistance of fuses curve c resettable ptcs c 140 120 percent of rating operating voltage rating general use 100 a b b 80 a 60 25°c 40 c 20 -60°c -76°f -40°c -40°f -20°c -4°f 0°c 32°f 20°c 68°f 40°c 104°f 60°c 140°f ambient temperature agency approvals littelfuse ptcs are recognized under the component program of underwriters laboratories to ul standard 1434 for thermistors the devices have also been certified under the csa component acceptance program © 2015 littelfuse inc specifications are subject to change without notice revised 11/05/15 80°c 176°f 100°c 212°f 120°c 248°f