document number: 50006 revision 19-mar-02 www.vishay.com 20 RCH vishay sfernice for technical questions, contact sfer@vishay.com power resistors, for mounting onto a heatsink thick film technology features 5 watt to 50w high power rating high overload capabilities high stability at rated power wide resistance range high thermal capacity easy mounting reduced size and weight high insulation: 10 6 m ? manufactured in cermet thic k lm technology, these power resistors exhibit remarkable characteristics and the series includes 4 types ranging from 5w to 50w designed to be mounted onto a heatsink, the resistors can bear high short time overloads and 3 types of terminations are available. the resistors are non inductive and are particularly suitable for high frequency operation and cut-out circuits. general tolerance: 0.3mm dimensions m odel RCH 5 RCH 10 RCH 25 RCH 50 l 16.6 19 28 47.8 w 9 11 14 15.5 h 16.4 20.6 27. 5 29.4 p leads pitch 10.2 12.7 1 8.3 30.5 f connections pitch 11.3 14.3 18.3 39.7 t 12.5 15.9 19. 8 21.4 s 5.3 5 7.7 8 d 2.4 2.4 3. 2 3.2 m2 m2 m3 m3 weight (g) 4 5 7 12 RCH...r RCH...v RCH...s dimensions in millimeters ? 2 6 m2 6 w h f s l ? d p 6 4.8 6 3 ? 2.1
www.vishay.com 21 RCH vishay sfernice document number: 50006 revision 19-mar-02 for technical questions, contact sfer@vishay.com mechanical specifications mechanical protection insulated case substrate alumina resistive element cermet connections tinned copper alloy environmental specifications temperature range - 55 c to + 125 c climatic category 55/125/56 power resistors for mounting onto a heatsink thick film technology resistance range 0.24 ? to 1m ? e24 series st andard resistance tolerances 1%, 2%, 5%, 10% p ower rating chassis mounted 5w to 50w unmounted 2w to 5.5w temperature coef cient 150ppm/ c (r > 1 ? ) insulation resistance 10 6 m ? total inductance 0.1h electrical specifications special features model RCH 5 RCH 10 RCH 25 RCH 50 power rating-chassis mounted 5w 10w 25w 50w power rating-unmounted 2w 2.5w 4w 5.5w thermal resistance rth (j-c) 4.8 c/w 3.2 c/w 1.4 c/w 0.8 c/w limiting element voltage (v rms ) 160v 250v 550v 1285v max. overload voltage (v rms ) 320v 500v 1100v 2500v dielectric strength (v rms ) 50hz 3000v 3000v 3500v 35 00v critical resistance 5120 ? 6250 ? 12100 ? 33024 ? resistance value in relation to tolerance and tcr resistance value < 1 ? > 1 ? standard 5% tolerances 10% standard t.c. 250ppm/ c 150ppm/ c tolerance on request 1% to 2% tests conditions typical drifts momentary overload 2pr/5s < (0.25% 0.05 ? ) us < 2 ul climatic sequence 5 cycles < (0.25% 0.05 ? ) nominal power pn - 55 c to + 155 c load life 1000h pr at + 25 c < (0.5% 0.05 ? ) humidity (steady state) 56 days r.h. 95% < (0.5% 0.0 5 ? ) performance
document number: 50006 revision 19-mar-02 www.vishay.com 22 RCH vishay sfernice for technical questions, contact sfer@vishay.com in order to improve the dissipation, either forced-air cooling or liquid cooling may be used. a low thermal radiation of the case allows several resistors to be mounted onto the same heatsink. do not forget to respect an insulation value between two resistors (dielectric strength in dry air 1kv/mm). in any case the hot spot temperature, measured locally on the case must not exceed 125 c. tests should be performed by the user. recommendations for mounting onto a heatsink surfaces in contact must be carefully cleaned. the heatsink must have an acceptable atness: from 0.05mm to 0.1mm/100mm. roughness of the heatsink must be around 6.3 m. in order to improve thermal conductivity, surfaces in contact (alumina, heatsink) are coated with a silicone grease (type sl 340 from rh ? ne-poulenc or dow 340 from dow corning). the fastening of the resistor to the heatsink is under pressure control of two screws (not supplied). tightening torque RCH 5 RCH 10 RCH 25 RCH 50 on heatsink 0.5nm 0.6nm 0.7nm 1nm power resistors for mounting onto a heatsink thick film technology choice of heatsink the user must choose the heatsink according to working conditions of the component (power, room temperature). maximum working temperature must not exceed 125 c. the dissipated power is simply calculated by the following ratio: p = p: expressed in w ? t: difference between maximum working temperature and room temperature. r th: (j-c): thermal resistance value measured between resistance layer and outer side of the resistor. it is the thermal resistance of the component (see special features table). r th: (c-a): thermal resistance value measured between outer side of the resistor and room temperature. it is the thermal resistance of the heatsink depending on the heatsink itself (type, shape) and the quality of the fastening device. example: r th: (c-a) for RCH 25 power rating 20w at ambient temperature + 50 c. ? t 125 c - 50 c 75 c r th ( j-c) = 1.4 c/w (special features) r th (j-c) + r th (c-a) = = = 3.75 c/w r th (c-a) 3.75 c/w - 1.4 c/w 2.35 c/w ? t [rt h (j-c) + rt h (c-a)] (1) ? t p 75 20
www.vishay.com 23 RCH vishay sfernice document number: 50006 revision 19-mar-02 for technical questions, contact sfer@vishay.com ordering information RCH 25 3.3k 5% r xxx model style resistance value tolerance connections custom desig n optional optional optional 1% s: flat with hole 2% r: round lead 5% v: m2 screw 10% power resistors for mounting onto a heatsink thick film technology overloads the applied voltage must always be lower than the maximum overload voltage as shown in the special features table. the values indicated on the graph below are applicable to resistors in air or mounted onto a heatsink. 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1000 100 10 1 0.1 energy in joules overload duration in seconds energy curve RCH 50 RCH 25 RCH 10 RCH 5 power rating chart for resistors mounted onto heatsink and thermal resistance of 1 c/w. to improve the thermal conductivity, surfaces in contact should be coated with a silicone grease. 0 20 40 60 80 100 120 140 % rated power ambient temperature in degrees celsius r c h 50 0 25 50 75 100 rc h 25 RCH 10 RCH 5 marking model, style, resistance value (in ), tolerance (in %), manufacturing date, vishay trade mark.
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