Components Derating(英文资料：器件的降级---随温度等因素,包括线插,线束,电阻,二极管等).doc

/Component_Derating_Guide_line.html#topConnector Voltage Derating:Derate connector voltage to 25% of rated operating voltage. Operating voltage = Connector rating * 0.25Derate connector operational temperature by 50oC. Connector rating = operating temperature + 50oCCurrent is normally specified as some number of pins carrying some specific amount of current, at some defined temperature. Increase the current carried over any particular pin and the number of pins carrying current most decrease. Decreasing the amount of current over the defined pins may allow more pins to carry current.The graph above shows the derating curves for a 2mm Hard Metric connector used in cPCI and other applications. In this case the graph provides three curves; Red Curve allowing all pins to carry currentBlue Curve allowing every other pin to carry current.Black Curve with only alternate pins on alternate rows carrying current.So in this case every pin on the connector can carry current Red, but each pin is limited to 1.6 amps, or about 1.4 amps at ambient temperature. However the black curve would normally be more realistic with only a quarter of the pins carrying current. Note that all three curves fall off at the same rate and end at a maximum temperature of 125C. However each curve starts with a different amount of maximum current at 0C based on the number of pins carrying current.Cable/Wire Derating:Refer to this page for a manufacturers listing of Wire and Cable. Cable manufacturers will provide different numbers based on the insulation used for the wire. The table below lists copper wire with a Teflon TFE insulation. Teflon insulation has a higher operation temperature range then other insulators, for example PVC. The table below is based on data derived from MIL-STD-975, using 70oC as the operating temperature. To derate based on number of wires in a bundle:IBW = ISW x (29 - #wire) / 28 1 to 15 Bundled wiresIBW = ISW x (0.5) more then 15 Bundled wiresISW = Single wireIBW = Bundled wiresTo derate by temperature use; derate by 80% at 1500C, 70% at 1350C, or 50% at 1050C Per MIL-STD-975To derate for Commercial wire use the table below;Copper Wire Correction Temperature Derate Ampacity 40oC 0.88 45oC 0.82 50oC 0.75 55oC 0.67 60oC 0.58 70oC 0.33 Ampacity Tables for many conditions (Commercial Wiring):IEEE Standard 835, IEEE Standard Power Cable Ampacity TablesIEEE Standard 848, Procedure for the Determination of the Ampacity De-rating of Fire Protected CablesICEA P-54-440, NEMA Pub. No. WC 51 - Ampacities of Cables in Open-Top TraysUse the National Electrical Code NEC system for premises wiring, and not the Military data on this page.Voltage Drop per Foot:V = I x L x (R/1000) x 1.004 x (T-20)V = Voltage Drop, I = Current, R = Resistance per 1000 footL = Length of wire in feet, T = Estimated wire Temperature under load oCRefer to the AWG Table for Resistance per length Copper Wire TFE Insulated AWG Current Carrying AWG Current Carrying 00 169 0 147 2 108 4 81 6 60 8 44 10 33 12 4425 14 19 16 13 18 9.2 20 6.5 22 4.5 24 3.3 26 2.5 28 1.8 30 1.3 - - Potentiometer Derating:Potentiometer Derating Curve Resistor Derating Example:Power ratings are normally specified at +25oC and must be reduced as the resistors temperature increases. A derating chart is often used, with derating starting at 70oC. Since parameters are application dependent, charts should be considered general rather than absolute, and only used as a guideline. However power de-rating curves should be considered more of a recommendation than a guideline The safest designs use the largest physical size operating at conservative temperatures and power ratings. Combining the resistor application and a power de-rating curve should start to form a design rule, once the location of the resistor on the PWB is known and the components around the device.Resistor Derating Chart % Rated load Wire WoundTemperature Metal FilmTemperature 100% 70oC 70oC 80% 110oC 85oC 60% 150oC 100oC 40% 190oC 120oC 20% 240oC 140oC 10% 260oC 145oC Design guidelines;For resistors mounted in series, consider the heat being conducted through the leads to the next resistor. At the same time axial lead-mounted parts also act as a heat dissipator and allow heat to be conducted away from the device and into the printed circuit card, or pads on the PCB. Of course heat is also removed from the component via convection and radiation.Large power resistors should be mounted to the metal chassis for heat dissipation. Do not mount resistors with power dissipation 1 Watt directly on terminal or printed wiring boards without use of heat sinks. A resistor that dissipates over one watt can damage a terminal board. A damaged board will have a lower insulation resistance. For the most efficient operation and even heat distribution, power resistors should be mounted in a horizontal position.MIL-R-39005 Fixed Wire Wound ResistorResistor Power ratings are normally specified at +25oC in the data sheet and must be reduced as the resistor temperature increases. A derating chart is often used, with derating starting at 70oC; however wire wound resistors Resistor Derating Curve below may operate up to 1250C before any derating is required. Since parameters are application dependent, power de-rating curves or charts should be considered general rather than absolute, and only used as a guideline.The safest designs use the largest physical size operating at conservative temperatures and power ratings. In this case MIL-R-39005 resistors are being used which define the type and size of the resistor Type RBR. Note that the vertical axis is Power Ratio derating factor and sets the recommended maximum power dissipation by temperature. MIL-39005 style resistors shall have a power rating based on continuous full-load operation at an ambient temperature of 125When higher ambient temperatures exist or when resistors are mounted in enclosures which limit ventilation, the wattage dissipation of any resistor should be reduced so that the maximum hot-spot temperatures permissible for the resistor is never exceeded under the most severe combination of temperature conditions. Note that the maximum permissible ambient temperature for a MIL-R-39005 style resistor is 1400C in still air. Wire-Wound ResistorFuse Derating: Fuses are specified to interrupt within a maximum of 5 seconds when driven at 200% of their rated current for nominal ratings up to and including 10 amperes. A fuse with a nominal rating of 15 amperes is specified to interrupt within a maximum of 10 seconds when driven at 200% of its rated current. The power supply shall be capable of delivering appropriate levels of current to achieve short fusing times. There is an additional derating of 0.2%/C for an increase in the temperature of fuse body. Main Fuse Derating Guidelines page. AC or DC Fuse operation. Fuse holders may also require derating.Recommended Fuse Stress Factor Fuse DeratingFuse Current Rating. Fuse Derating Factor2 - 1.5 amps0.501 - 1.5 amps0.450.5 - 0.75 amps0.400.375 amps0.350.25 amps0.300.125 amps0.25Derate a fuse by multiplying the rated current by the derating factor.Derate an additional 0.5%/C above 250C Keep in mind that a fuse holder, if used should be derated as well. When selecting a fuse holder be sure that the holder can withstand the maximum fuse rating for voltage and current. The fuse holder could melt trying to with stand the power dissipated by the fuse before the fuse opens.No derating data has been found for a Fuse Holder; How ever in many cases a connector is derated to 25% of its maximum Dielectric Withstanding Voltage. Or the dielectric should with stand Ambient Temp + Ohmic heating Temp + 50C Fuses are specified to interrupt within a maximum of 5 seconds when driven at 200% of their rated current for nominal ratings up to and including 10 amperes. A fuse with a nominal rating of 15 amperes is specified to interrupt within a maximum of 10 seconds when driven at 200% of its rated current.The power supply shall be capable of delivering appropriate levels of current to achieve short fusing times. There is an additional derating of 0.2%/C for an increase in the temperature of fuse body.Switch Derating: Switch Temperature Correction Current Derating Factor Application Ambient Temperature Military Commercial Load Type 0oC to 85oC Above 85oC 0oC to 85oC Above 85oC Resistive 75% of ratedResistive load 60% of ratedResistive load 75% of ratedResistive load 60% of ratedResistive load Inductive /Motor 75% of ratedInductive load 60% of ratedInductive load 40% of ratedResistive load 30% of ratedResistive load Capacitive /Lamp 75% of ratedCapacitive load 60% of ratedCapacitive load 25% of ratedResistive load 20% of ratedResistive load Inductor Derating: Inductor Temperature Correction Current Derating Factor Application Ambient Temperature Military Commercial Load Type 0oC to 85oC Above 85oC 0oC to 85oC Above 85oC Resistive 75% of ratedResistive load 60% of ratedResistive load 75% of ratedResistive load 60% of ratedResistive load Inductive /Motor 75% of ratedInductive load 60% of ratedInductive load 40% of ratedResistive load 30% of ratedResistive load Capacitive /Lamp 75% of ratedCapacitive load 60% of ratedCapacitive load 25% of ratedResistive load 20% of ratedResistive load EMI Filter Derating:The general recommendation is to derate an EMI Filter to 50% of rated voltage and 50% of rated current, using a maximum temperature of 850C.However that could be to strict for some applications, in which cause the next best option would be the dearting curve provided in the data sheet.This example shows 50% operation doesnt apply until 125C and maximum operation out to 150C Case Temperature.A manufacturers listing of EMI/RFI ComponentsNote that many temperature-power derating curves are just a linear curve or set of curves, others are a bit more complicated.Some curves show maximum power dissipation, others show percent rated load as current or voltage.EMI Chip Derating Curve Diode Derating:Diode Temperature Correction Diode Type Critical Stress Parameter Derating Maximum Junction Temp General Purpose,Rectifier, Switching,PIN/Schottky, Thyristors PIV 0.70 125oC Surge Current 0.50 Forward Current 0.50 Varactor Power 0.50 125oC Reverse Voltage 0.75 Forward Current 0.75 Voltage Regulator Power 0.50 12