GE Sensing Features Applications * Low cost, solid state device for inrush current suppression Control of the inrush current in switching power supplies, flourescent lamp, inverters, motors, etc. * Excellent mechanical strength * Low steady resistance and accompanying power loss * Wide operating temperature range: -58F to 347F (-50C to 175C) * Small size * Low cost solid state sensor * Suitable for PCB mounting * Available as a standard with kinked or straight leads and on tape and reel to EIS RS-468A for automatic insertion NTC Inrush Current Limiter Thermometrics Thermistors NTC Inrush Current Limiter is a Thermometrics product. Thermometrics has joined other GE high-technology sensing businesses under a new name-- GE Industrial, Sensing. g GE Sensing Options Type CL Specifications * * * * * NTC discs for inrush current limiting Data Description *maximum rating at 77F (25C) or Iderated = (1.1425-0.0057 x TA) x Imax @ 77F (25C) for ambient temperatures other than 77F (25C). **maximum ratings ***R0=X1Y where X and Y are found in the table below Disc thermistor with uninsulated lead-wires. Type Fig. 1 Res @ 77F (25C) 25% ) ( CL-11 0.7 Max* Steady State Current AMPS (RMS) 12 CL-21 1.3 8 CL-30 2.5 8 CL-40 5 6 CL-50 7 5 CL-60 10 5 CL-70 16 4 CL-80 47 3 CL-90 120 2 CL-101 0.5 16 CL-110 10 3.2 CL-120 10 1.7 CL-130 50 1.6 CL-140 50 1.1 CL-150 5 4.7 CL-160 5 2.8 CL-170 16 2.7 CL-180 16 1.7 CL-190 25 2.4 CL-200 25 1.7 CL-210 30 1.5 For kinked leads, add suffix "A" For tape and reel, add suffix "B" Other tolerances in the range 0.7 to 120 Other tolerances, tolerances at other temperatures Alternative lead lengths, lead materials, insulations Disc Dia. (Max) in (mm) Disc Thick. (Max) in (mm) Lead Lead Spacing Dia. (Ref.) AWG in (mm) Cx (max)** Farads Equation constants for resistance under load *** @120 VAC @240 VAC X Y 0.77 (19.55) 0.55 (13.97) 0.77 (19.55) 0.77 (19.55) 0.77 (19.55) 0.77 (19.55) 0.77 (19.55) 0.77 (19.55) 0.93 (23.62) 0.93 (23.62) 0.40 (10.16) 0.40 (10.16) 0.45 (11.45) 0.45 (11.45) 0.55 (13.97) 0.55 (13.97) 0.55 (13.97) 0.55 (13.97) 0.55 (13.97) 0.55 (13.97) 0.40 (10.16) 0.22 (5.58) 0.21 (5.334) 0.22 (5.58) 0.22 (5.58) 0.26 (6.60) 0.22 (5.58) 0.22 (5.58) 0.22 (5.58) 0.22 (5.58) 0.22 (5.58) 0.17 (4.31) 0.17 (4.31) 0.17 (4.31) 0.17 (4.31) 0.18 (4.57) 0.18 (4.57) 0.18 (4.57) 0.18 (4.57) 0.18 (4.57) 0.18 (4.57) 0.20 (5.08) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.250 (6.35) 0.250 (6.35) 0.250 (6.35) 0.250 (6.35) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.328 (8.33) 0.250 (6.35) 18 2700 600 0.50 18 800 200 18 6000 18 Approx. Res. Under Load at % Maximum Rated Current 50% 75% 100% -1.18 Current 25% Range Min. I / Max. I 4.0 112 14 0.02 Diss. Const. (mW/C) 25 Time Const. (sec.) 100 0.06 0.04 0.60 -1.25 3.0 1 8.0 0.25 0.09 0.06 0.04 15 60 1500 0.81 -1.25 2.5 1 8.0 0.34 0.14 0.09 0.06 25 100 5200 1300 1.09 -1.27 1.5 1 6.0 0.65 0.27 0.16 0.11 25 100 18 5000 1250 1.28 -1.27 1.5 1 5.0 0.96 0.40 0.24 0.16 25 120 18 5000 1250 1.45 -1.30 1.2 1 5.0 1.09 0.44 0.26 0.18 25 100 18 5000 1250 1.55 -1.26 1.0 1 4.0 1.55 0.65 0.39 0.27 25 100 18 5000 1250 2.03 -1.29 0.5 1 3.0 2.94 1.20 0.71 0.49 25 100 18 5000 1250 3.04 -1.36 0.5 1 2.0 7.80 3.04 1.75 1.18 30 120 18 4000 1000 0.44 -1.12 4.0 1 16 0.09 0.04 0.03 0.02 30 120 24 600 150 0.83 -1.29 0.7 1 3.2 1.10 0.45 0.27 0.18 8 30 24 600 150 0.61 -1.09 0.4 1 1.7 1.55 0.73 0.46 0.34 4 90 24 600 150 1.45 -1.38 0.4 1 1.6 5.13 1.97 1.13 0.75 8 30 24 600 150 1.01 -1.28 0.2 1 1.1 5.27 2.17 1.28 0.89 4 90 22 1600 400 0.81 -1.26 1.0 1 4.7 0.66 0.27 0.16 0.11 15 110 22 1600 400 0.60 -1.05 0.8 1 2.8 0.87 0.42 0.27 0.20 9 130 22 1600 400 1.18 -1.28 0.5 1 2.7 1.95 0.80 0.48 0.33 15 110 22 1600 400 0.92 -1.18 0.4 1 1.7 2.52 1.11 0.69 0.49 9 130 22 800 200 1.33 -1.34 0.5 1 2.4 2.63 1.04 0.60 0.41 15 110 22 800 200 0.95 -1.24 0.4 1 1.7 2.74 1.18 0.70 0.49 9 130 24 600 150 1.02 -1.35 0.3 1 1.5 3.83 1.50 0.87 0.60 8 30 GE Sensing In the circuit above the maximum current at turn-on is the peak line voltage divided by the value of R; for 120 V, it is approximately 120 x 2/RI. Ideally, during turn-on RI should be very large, and after the supply is operating, should be reduced to zero. The NTC thermistor is ideally suited for this application. It limits surge current by functioning as a power resistor which drops from a high cold resistance to a low hot resistance when heated by the current flowing through it. Some of the factors to consider when designing NTC thermistor as an inrush current limiter are: * * * * * Maximum permissible surge current at turn-on Matching the thermistor to the size of the filter capacitors Maximum value of steady state current Maximum ambient temperature Expected life of the power supply Maximum Surge Current The main purpose of limiting inrush current is to prevent components in series with the input to the DC/DC convertor from being damaged. Typically, inrush protection prevents nuisance blowing of fuses or breakers as well as welding of switch contacts. Since most thermistor materials are very nearly ohmic at any given temperature, the minimum no-load resistance of the thermistor is calculated by dividing the peak input voltage by the maximum permissible surge current in the power supply (Vpeak/Imax surge). Energy Surge at Turn-On At the moment the circuit is energized, the filter caps in a switcher appear like a short circuit which, in a relatively short period of time, will store an amount of energy equal to 1/2CV2. All of the charge that the filter capacitors store must flow through the thermistor. The net effect of this large current surge is to increase the temperature of the thermistor very rapidly during the period the capacitors are charging. The amount of energy generated in the thermistor during this capacitor-charging period is dependent on the voltage waveform of the source charging the capacitors. However, a good approximation for the energy generated by the thermistor during this period is 1/2CV2 (energy stored in the filter capacitor). The ability of the NTC thermistor to handle this energy surge is largely a function of the mass of the device. This logic can be seen in the energy balance equation for a thermistor being self-heated: Input Energy = Energy Stored + Energy Dissipated ~ RI -to DC/DC converter Inrush CurrentLimiters In Switching Power Supplies The problem of current surges in switch-mode power supplies is caused by the large filter capacitors used to smooth the ripple in the rectified 60 Hz current prior to being chopped at a high frequency. The diagram above illustrates a circuit commonly used in switching power supplies. Typical power supply circuit or in differential form: Pdt = HdT + (T - TA)dt where: P = Power generated in the NTC t = Time H = Heat capacity of the thermistor T = Temperature of the thermistor body = Dissipation constant TA = Ambient temperature During the short time that the capacitors are charging (usually less than 0.1 second), very little energy is dissipated. Most of the input energy is stored as heat in the thermistor body. In the table of standard inrush limiters there is listed a recommended value of maximum capacitance at 120 V and 240 V. This rating is not intended to define the absolute capabilities of the thermistors; instead, it is an experimentally determined value beyond which there may be some reduction in the life of the inrush current limiter. Maximum Steady-State Current The maximum steady-state current rating of a thermistor is mainly determined by the acceptable life of the final products for which the thermistor becomes a component. In the steady-state condition, the energy balance in the differential equation already given reduces to the following heat balance formula: Power = I2R = (T - TA) As more current flows through the device, its steady-state operating temperature will increase and its resistance will decrease. The maximum current rating correlates to a maximum allowable temperature. In the table of standard inrush current limiters is a list of values for resistance under load for each unit, as well as a recommended maximum steady-state current. These ratings are based upon standard PC board heat sinking, with no air flow, at an ambient temperature of 77 (25C). However, most power supplies have some air flow, which further enhances the safety margin that is already built into the maximum current rating. To derate the maximum steady state current for operation at elevated ambient temperatures, use the following equation: Iderated = Iderated = (1.1425-0.0057 x TA) x Imax @ 77F (25C) GE Sensing Power Thermistor Specification For the Reduction of Inrush Current A power thermistor is a type of NTC thermistor used for the reduction of large inrush currents. These large inrush currents are typically caused by charging of filter capacitors in switching power supplies. ~ Parts 7 9 11 13 15 18 Outside Kink: F 9 Straight: D 11 No: M 13 Yes: J 15 d W1 Units: in (mm) 18 D F H1 L L C +P: Th Power thermistor application circuits 7 Y-Form L C +- ~ EH D 7.01.5 9.01.5 11.01.5 13.51.5 15.01.5 18.01.5 Diam (mm) Inside Kink: E C +- Parts Type Lead Wire Style P: Th P: Th 5W TP7D7 TP8D7 TP10D7 TP16D7 TP22D7 TP5D9 TP8D9 TP10D9 TP16D9 TP4R7D11 TP5D11 TP8D11 TP10D11 TP4R7D13 TP5D13 TP8D13 TP10D13 TP3D15 TP5D15 TP8D15 TP10D15 TP4D18 TP5D18 TP8D18 TP10D18 T(max.) 5.2 6.0 6.5 8.0 9.0 9.0 Normal no load resistance ) ( 7 8 10 16 22 5 8 10 16 4.7 5 8 10 4.7 5 8 10 3 5 8 10 4 5 8 10 L 18.5 18.5 18.5 18.5 18.5 18.5 d 0.6 0.6 0.8 0.8 0.8 1.0 F 5.0 5.0 7.5 7.5 7.5 10.0 H1(2.5) 15.5 17.0 19.5 21.5 23.5 27.0 Normal Dissipation Max. constant factor Permissible (K) (mW/C) Current at 77F (25C) 3000 9.8 2.4 3000 10.0 2.3 3000 10.3 2.0 3000 10.5 1.6 3100 9.5 1.4 3000 11.0 3.0 3000 14.2 2.7 3000 12.9 2.3 3100 10.2 1.7 3000 15.0 3.7 3000 15.0 3.3 3000 17.6 2.6 3100 17.4 2.4 3000 15.0 4.3 3000 15.0 3.4 3100 17.0 2.7 3100 13.8 2.5 3000 16.5 4.0 3100 17.7 3.7 3100 21.7 3.1 3100 19.9 2.9 3000 22.2 4.1 3000 24.0 3.8 3100 26.8 3.1 3100 27.8 2.8 W1(min.) 1.5 1.5 2.0 2.0 2.0 3.0 Time Constant (sec) 70 70 80 100 120 110 120 130 160 90 130 160 170 110 125 160 180 165 170 180 200 170 180 220 260 * The resistance tolerance is 10% for standard devices. * The b constant is determined by the equation : = 1779.7 ln (R25/R85) ...R25 and R85 represent the thermistor resistance at 77F and 185F (25C and 85C) respectively. * For non-standard devices consult Thermometrics global business. Code Designation T Resin coated Pb/Sn-plated copper wire Power thermistor standard dimensions TP 8 1 1 2 3 4/5 6 2 3 4 5 6 7 8 9 10 11 Shape: Power thermistor Resistance at 77F (25C): 8 = 8 S, 4R7 = 4.7 S Diameter size: D7, D9, ...D18 Resistance and B constant tolerance: K: 10%, L: 15% Lead wire center-to-center: (F): A: 0.19 in (5 mm), B: 0.29 in (7.5 mm), C: 0.39 in (10 mm) Lead wire style: D: Straight, E: Inside kink, F: Outside kink Lead wire length: G: 0.19 in (5 mm), H: 0.27 in (7 mm), I: 0.35 in (9 mm), ...S: Other dimensions Y-Form: J: Yes, M: No MK part number marking: N: No, O: Yes Packing form: Taping P: 15 pitch, Q: 30 pitch, Others: R: Bulk, S: Paper pad, T: Element 7 8 g 9 10 11 (c)2006 GE. All rights reserved. 920-325A D 13 L All specifications are subject to change for product improvement without notice. GE(R) is a registered trademark of General Electric Co. 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