FEATURES SPECIFICATIONS * Ideal for medical surge protection applications * Ideal to replace standard carbon composition resistors * Custom dimensions, values, tolerances and characteristics available Material Resistive Element: Thick Film Encapsulation: Screen Printed Glass Electrical 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 Resistors Thick Film Non Inductive C A B 0.50mm H E 0.25mm SINGLE PULSE ENERGY RATING C = Capacitance (farads) 4. Refer to the Pulse Chart. On this chart find the point where the energy ratio (Er), found at step 3, and time (ta) 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. 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 voltage of 3.5kV is acceptable. 1 Ea = -- CV2 = 6.1J 2 ta = R C = 1 ms 6.1J Er = --- 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 Er of 18%, which is below the energy curve. 6.1J Er = --- x 100 = 18% 33J U (KV) 3 3.5 4 7 7 11 Type TFSA TFSB TFSC TFSD TFSE TFSF Energy* (J) 6 9 11 33 44 55 Power (W) 0.5 0.5 0.75 1 1.5 2 Dimensions (mm) B C H 5.5 10 0.7 5.5 10 0.7 5.5 10 0.7 8 10 0.9 10.5 10 0.9 10.5 10 0.9 A 9 11 13 21 21 26 E 1.1 1.1 1.1 1.3 1.3 1.3 *Published energy rating is for 10ms pulse. For shorter pulses energy rating has to be derated according to Max. Individual Pulse Rating chart (below) and Single Pulse Energy Rating considerations (left). O R D E R I N G I N F O R M AT I O N RoHS Compliant Series Ohm Value Type See chart Example: 100R = 100 2K40 = 2400 Tolerance F = 1% G = 2% J = 5% K = 10% MAXIMUM INDIVIDUAL PULSE RATING 1000 Energy Rating % Although Ohmite's 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 V2t film. This application note can guide V E = --- R you through these considerations. t For applications with transients, pulses or surges the following must E=1 -CV2 be considered: V 2 1. Do not exceed the normal rated t = RC operating voltage of the device. t 2. Using the figure at right, estimate the energy (Ea) and the pulse duraV2t V E = --- tion (ta) for a single pulse in your 3R application. t 3. Calculate the energy ratio in percent (Er) between the nominal energy rating of the model you V2t V E = --- 3R have chosen (see table) and the single pulse energy in your applit cation (Ea from step 2) using the (joules) E = Energy formula: t = Time (seconds) Ea V = Voltage (volts) Er = -------- x 100 R = Resistance (ohms) Enominal 100 10 1 0.1 1 s 10 s 100 s 1 ms Pulse Width 10 ms 100 ms NOTES * For pulses over 100ms, refer to the momentary overload specification on the product data sheet. Always verify designs with pulse and surge conditions through thorough testing of the design at maximum operating temperature 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. Ohmite Mfg. Co. 1600 Golf Rd., Suite 850, Rolling Meadows, IL 60008 * Tel. 1-866-9-OHMITE * Fax 1-847-574-7522 * www.ohmite.com * info@ohmite.com 51