1-866-9-ohmite ? intl 1-847-258-0300 ? fax 1-847-574-7522 ? www.ohmite.com ? info@ohmite.com 57 characteristics resistive element thick film encapsulation screen printed glass resistance value 100 up to 100k temperature coefficient 100ppm/c tolerance 1%, 2%, 5%, 10% operating temperature -55c to +200c test vde 0750 (pulse duration 10 msec) tfs series surge capable thick film non inductive type u (kv) energy* (j) power (w) tfsa 3 6 0.5 tfsb 3.5 9 0.5 tfsc 4 11 0.75 tfsd 7 33 1 tfse 7 44 1.5 tfsf 11 55 2 *published energy rating is for 10ms pulse. for shorter pulses energy rat - ing has to be derated according to max. individual pulse rating chart and single pulse energy rating considerations. f e a t u r e s ? appropriate for medical surge protec- tion applications ? ideal to replace standard carbon com- position resistors ? custom dimensions, values, toler - ances and characteristics available notes ? momentary overload capability is 5 times rated power for 1 second or 2 times rated power for 5 seconds. always verify designs with pulse and surge condi - tions through thorough testing of the design at maximum operating tempera - ture and maximum pulse loading (or some margin above maximum pulse loading). ? damage to the resistor by excessive pulse loading is generally indicated by an increasing resistance of the resistor. ? energy ratings are based on single pulses (at least 1 minute between pulses). ? for multiple pulse applications the energy pulse rating should be reduced and the average power should not exceed the nominal power rating of the selected model. ? see single pulse energy section for more information the tfs series has been specifically developed to absorb large amounts of energy by efficient use of its compact mass. ideal for medical surge protection applications, these thick film resis- tors offer non-inductive performance in an axial package. uses include power supply conversion, electron microscopes, x-ray systems, high-resolution crt displays, and geophysical instrument related products. series specif ications a c b he 0.50mm 0.25mm type watts a b c h e tfsa 0.5 9 5.5 10 0.7 1.1 tfsb 0.5 11 5.5 10 0.7 1.1 tfsc 0.75 13 5.5 10 0.7 1.1 tfsd 1 21 8 10 0.9 1.3 tfse 1.5 21 10.5 10 0.9 1.3 tfsf 2 26 10.5 10 0.9 1.3 dimensions mm (continued)
1-866-9-ohmite ? intl 1-847-258-0300 ? fax 1-847-574-7522 ? www.ohmite.com ? info@ohmite.com 58 although ohmites tfs series resistors have been specially designed and developed to absorb much more energy than standard resistors, pulses and transients require special consideration since they cause an instantaneous temperature rise in the resistor film. this application note can guide you through these considerations. for applications with transients, pulses or surges the following must be consid - ered: 1. do not exceed the normal rated oper - ating voltage of the device. 2. using the figure at right, estimate the energy (e a ) and the pulse duration (t a ) for a single pulse in your applica - tion. 3. calculate the energy ratio in percent (e r ) between the nominal energy rat - ing of the model you have chosen (see table) and the single pulse energy in your application (e a from step 2) using the formula: e a e r = CCCCCCCC x 100 e nominal 4. refer to the pulse chart. on this chart find the point where the energy ratio (e r ), found at step 3, and time (t a ) coincide. qualify that this point falls below the maximum pulse energy curve. if the point is above the curve a bigger model should be chosen. v t v t v t v t e = ??? v 2 t r e = ??? v 2 t 3r e = ??? v 2 t 3r e= energy (joules) t= t ime (seconds) v= v oltage (volts) r= resistance (ohms) c= capacitance (farads) e = ?cv 2 1 2 t = rc example a 1f capacitor is charged to 3.5kv and model tfsc, 1kohm has been selected. model tfsc is rated for 4kv, so the peak volt - age of 3.5kv is acceptable. 1 e a = CC cv 2 = 6.1j 2 t a = r c = 1 ms 6.1j e r = CCC x 100 = 55% 11j according to the pulse chart, an energy ratio of 55% for a pulse width of 1ms falls well above the energy curve. the limit is actually located around 25-30%. model tfsc cannot be used for this application. a bigger model should be chosen, for example tfsd. model tfsd, 1kohm, can be used for this application because we have an energy ratio e r of 18%, which is below the energy curve. 6.1j e r = CCC x 100 = 18% 33j ohm v alue example: 100r = 100? 2k40 = 2400? t olerance f = 1% g = 2% j = 5% k = 10% series tfsa100kje energy rating joules a= 6 b= 9 c= 11 rohs compliant d= 33 e= 44 f= 55 standard part numbers for tfs series 6 joules 9 joules 11 joules 33 joules 44 joules 55 joules ohms tol. 0.5 watts 0.5 watts 0.75 watts 1 watts 1.5 watts 2 watts 100 1% tfsa100rfe 100 5% tfsb100rje tfsd100rje tfsf100rje 220 1% tfsa220rfe 270 5% tfsa270rje tfsc270rje tfsd270rje tfsf270rje 470 1% tfsa470rfe 470 5% tfsb470rje tfse470rje 680 5% tfsa680rje tfsc680rje tfse680rje tfsf680rje 750 5% tfsb750rje tfsd750rje tfsf750rje 1,000 1% tfsa1k00fe 1,000 5% tfsa1k00je tfsb1k00je tfsc1k00je tfsd1k00je tfse1k00je tfsf1k00je 1,500 5% tfsa1k50je tfsc1k50je tfsd1k50je tfsf1k50je 2,200 1% tfsa2k20fe 2,700 5% tfsb2k70je tfse2k70je 4,700 1% tfsa4k70fe 4,700 5% tfsa4k70je tfsc4k70je tfsd4k70je 4,990 1% tfsa4k99fe 5,000 5% tfsa75k0je 6,800 5% tfsb6k80je tfse6k80je 10,000 1% tfsa10k0fe 10,000 5% tfsa10k0je tfsb10k0je tfsc10k0je tfsd10k0je tfsf10k0je 16,000 5% tfsf16k0je 20,000 1% tfsa20k0fe tfsf20k0je 20,000 5% tfsb20k0je tfsd20k0je 22,000 1% tfsa22k0fe 27,000 5% tfsa27k0je tfsc27k0je tfse27k0je 47,000 1% tfsa47k0fe 50,000 5% tfsa50k0je tfsf51k0je 51,000 5% tfsb51k0je tfsc51k0je tfsd51k0je 75,000 5% TFSE75K0JE 100,000 1% tfsa100kfe 100,000 5% tfsb100kje tfsc100kje tfsd100kje tfsf100kje tfs series surge capable thick film non inductive single pulse energy r ating o rdering inf ormation maximum individual pulse rating energy rating % pulse width 1s 10s 100s 1 ms 10 ms 100 ms 0.1 1000 1 10 100
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