BJT Temperature-Power Derating Curves
Complete List [below], NPN BJT Derating curves, PNP BJT Derating curves
2N718a Derating Curves, NPN, General Purpose Transistor, TO-18 package
2N930 Derating Curves, NPN, Low Power Transistor, TO-18 package, SMD
2N1613 Derating Curves, NPN, Medium Power Transistor
2N1711 Derating Curves, NPN, Low Power Transistor
2N2218 Derating Curves, NPN, Low Power Transistor
2N2219 Derating Curves, NPN, Low Power Transistor [Same graph as 2N2218]
2N2221 Derating Curves Case TO18, NPN Switching Transistor [Same as 2N2222]
2N2222 Derating Curves Case TO18, NPN Switching Transistor, General Purpose
2N2432 Derating Curves, NPN, Low Power Transistor, TO-18, SMD Devices
2N2484 Derating Curves NPN Amplifier Transistor, TO-18 metal Can and SMD devices
2N2604 Derating Curves, PNP Silicon Low Power Transistor, TO-46 metal Can, SMD device
2N2904 Derating Curves, PNP General Purpose Transistor, TO-39 package
2N2906 Derating Curves, PNP General Purpose Transistor, TO-18 metal Can and SMD Cases
2N2944 Derating Curves, PNP Switching Transistor
2N3019 Derating Curves, NPN Low Power Transistor
2N3055 Derating Curves, NPN Power Transistor
2N3250A Derating Curves, PNP Switching Transistor
2N3418 Derating Curves, NPN Medium Power Transistor, TO-39, TO-5, SMD
2N3439 Derating Curves, NPN Low Power Transistor
2N3441 Derating Curves, NPN Medium Power Transistor
2N3467 Derating Curves, PNP Switching Transistor
2N3485A Derating Curves, PNP Switching Transistor
2N3498 Derating Curves, NPN Switching Transistor, BJT
2N3634 Derating Curves, PNP High Voltage Transistor
2N3715 Derating Curves, NPN High-Power Transistor
2N3739 Derating Curves, NPN Power Transistor
2N3740 Derating Curve, PNP Power Transistor, TO-66, and SMD styles
2N3743 Derating Curves, PNP High Voltage Transistor, TO-39 metal Can, SMD
2N3762 Derating Curves, PNP Switching Transistor, TO-39 Can, and SMD Packages
2N3764 Derating Curves, 2N3765 PNP Switching Transistor
2N3791 Derating Curves, PNP High Voltage Transistor
2N3846 Derating Curves, NPN Power Transistor, TO-63 Stud-Mount, TO-254, TO-257
2N3867 Derating Curve, PNP Low Power Transistor
2N4029 Derating Curves, PNP Low Power Transistor, TO-18 metal Can
2N4033 Derating Curves, PNP Low Power Transistor, TO-18 Thou-hole and SMD packages
2N4150 Derating Curves, NPN Low Power Transistor, TO-5 metal can
2N4237 Derating Curves, NPN Transistor, TO-39 metal Can
2N4238 Derating Curves, NPN Transistor, TO-39 metal Can
2N4239 Derating Curves, NPN Transistor, TO-39 metal Can
2N4930 Derating Curves, PNP High Voltage Transistor, TO-39 Can, SMD Packages
2N4931 Derating Curves, PNP High Voltage Transistor, TO-39, SMD Packages
2N5002 Derating Curves, NPN High Power Transistor, TO-59 package
2N5003 Derating Curves, PNP High Power Transistor, TO-59 package
2N5004 Derating Curve, NPN High Power Transistor, TO-59 package
2N5005 Derating Curves, PNP High Power Transistor, TO-59 package
2N5151 Derating Curves, PNP Power Transistor, TO-205 package
2N5153 Derating Curves, PNP Power Transistor, TO-205 package
2N5339 Derating Curves, PNP Power Transistor, TO-39 package
2N5581 Derating Curves, NPN Switching Transistor, TO-46 metal can
2N6193 Derating Curves, PNP Switching Transistor, TO-39 metal can
2N6249 Derating Curves, NPN Power Transistor, TO-3, TO-257 packages
2N6300 Derating Curves, NPN Power Transistor, TO-66 Package
2N6301 Derating Curves, NPN Power Transistor, TO-66 Package
2N6306 Derating Curves, NPN Power Transistor, TO-3 Can and TO-254, TO-257 Tab Mount
2N6546 Derating Curves, NPN Power Transistor, TO-3, TO-257 packages
2N6676 Derating Curves, NPN Power Transistor, TO-3 Case and TO-254, TO-257 Tab Mount
2N6691 Derating Curves, NPN Power Transistor, TO-61 Case
Transistor Derating
Use the Transistor Curves in the table to determine how much to derate operational wattage over temperature. The Temperature-Power Derating Curves relate to only the device in ambient temperature. In some cases, in addition to the curve an equation may also be provided to show the reduction in power dissipation; watts/temperature increase. Many vendor data sheets only provide derating conversion [Derating Factor], with out the curves.
If the final design places one or more devices near the transistor package which result in radiant heat than the derating graph must be shifted lower to account for that heat source. However the opposite is also true as the graphs do not account for attached heat sinks or forced air cooling. Applying a heat sink or implementing forced air cooling will allow the transistor to operate above what the curve indicates. Pulsed circuits, or transistors that are switched off more than they conduct may not require as much derating as a transistor which is on and conducting much of the time.
When in doubt use a derating factor, or stress ratio of 75% [of maximum power dissipation] as a guideline.
Transistor Stress Ratio = Operating Power / Rated Power = 75%
Transistor Derating Definitions:
Absolute Maximum Rating. These ratings are limiting values beyond which the serviceability of
any individual semiconductor device may be impaired..
Altitude. Unless other-wise stated the derating curves assume a normal altitude of sea-level. Additional component derating may be required for an altitude above sea-level. For operation under conditions of very low atmospheric pressure or space vacuum heat loss by convection is essentially zero, while ambient temperature is the maximum temperature of the heat sink
or other mounting surface in contact with the part, or the temperature of the surface of the part
itself (case temperature).
Ambient temperature. Ambient temperature is the air temperature measured below a semiconductor device,
in an environment of substantially uniform temperature, cooled only by natural air convection [Free-Air], and not materially
affected by reflective and radiant surfaces. Note Free-Air is also called Still-Air, and also implies that the device is not installed with an electronic chassis that would restrict air flow.
Case mount. A type of semiconductor package (outline) which provides a method of readily attaching one surface of the
semiconductor device to a heat dissipater to achieve thermal management of the case temperature. A TO-3 metal package is an example of a case mount device. Another form of a case mount device is a TO-257 which uses a metal tab as a heat sink mounting location [see Tab Mount]. Some devices have one of the leads connected to the case, while in other instances the case is isolated from the terminals.
Case temperature. Case temperature is that temperature measured at a specified point on the case of a
semiconductor device. In some cases a transistor derating curve is provided for ambient temperature, while in other cases the curve covers case temperature. In either case the derating curve indicates what factor is being measured. Temperature-Power derating curves are also provided for a particular transistor case style without regard any semiconductor device.
Celsius. A temperature scale that defines ooC as the freezing point of water and 100oC as the boiling point of water [at standard atmospheric pressure]. The Celsius scale is used on all data sheets and derating curves. To convert from Celsius to Fahrenheit use; F = (9/5) x C +32.
Chassis Mount. See Stud Mount.
Conduction is the transfer of heat through solid objects. Heat conduction is the method of heat transfer from a semiconductor package and its heat sink, or the transfer of heat from the junction and the case of a transistor. Conduction is the most effective way to transfer heat away from the semiconductor junction.
Convection is the transfer of heat through air [or gases and liquids]. Heat conduction is the method of heat transfer from a transistor case or heat sink and the surrounding air. Heat convection is used as the heat transfer method for derating curves and equations for most semiconductors. Convection is the most effective way to transfer heat away from the semiconductor case and into the surrounding ambient air.
Derate the process of reducing the operational capabilities of a device to allow it to operate at higher temperatures. A policy of deliberately under stressing components in order to provide increased reliability, by reducing thermal and electrical stress to the component.
Enclosure. An electronic chassis that encloses a device. The semiconductor curves do not account for an enclosure and assume free-air. Also called a chassis or case.
Forced Air. The application of an air source via a fan, usually given in cubic foot per minute [CFM]. Fans are normally selected by the amount of forced air they provide [CFM] or their size in dimensions in millimeters or both characteristics. Mechanical fans are also supplied as either AC or DC operating fans, watch the change in Mean Time Between Failure [MTBF].
Guideline. Many of the component derating pages provide guidelines or recommendations for safely operating the device over temperature. The curves for the devices listed above should be considered rules to insure that the junction temperature is held under the absolute maximum limits provided within the manufacturers data sheet.
Grouping. or Component Grouping occurs when a near-by device imparts radiant heat onto the Device-Under-Test [DUT]. Component grouping is not accounted for in the derating curves.
Heat Sink. A metallic device that dissipates or radiates heat into the surrounding which is generated form an integrated circuit or other device. There are a number of Materials used for heat sinks; Aluminum, Brass, Bronze and Black anodized. There also a large section of heat sink styles; to include, Folded Fins, Bonded or Fabricated Fins, or Stampings. The point of the heat sink is to increase the surface area effected by the surrounding air. Most air cooled heat sinks are convection limited, and the overall thermal performance of an air cooled heat sink can often be improved significantly if more surface area can be exposed to the air stream. Such high performance heat sinks utilize thermally conductive aluminum-filled epoxy to bond planar fins onto a grooved extrusion base plate. metal heat sinks are available for plastic packages as well as metal cans. However; Heat sinks for TO-92 plastic packages may be available, but their thermal resistance is very high. [Heat Sink Vendors]
Hermetically Sealed. An air tight seal.
Mounting. See Case Mount, Tab Mount, or Stud Mount.
MTBF. Mean Time Between Failure. Definition of MTBF
Room temperature. is normally taken to be 210 Celsius. While ambient temperature is described in data sheets as 250C, or another 90F hotter than room temp. So in general a data sheet's rating will be referring to a temperature of 770 Fahrenheit.
Safe Operating Area [SOA]. The area bounded under a curve such that the combination of maximum current and maximum voltage are not exceeded. 2N3637 Safe Operating Area Graph.
Storage temperature. The maximum and Minimum storage temperature is a temperature at which the device may be stored without any
power being applied. The storage temperature always covers operational temperature at a minimum. Excessively hot temperatures can damage the die-to-case bond, damage the package or alter the electrical or thermal characteristics. Excessively cold temperatures can cause cracking of the chip. Always check the data sheet for the proper storage temperature.
Stress Rating is defined as the ratio of applied stress to rated stress. Types of stress include; temperature, voltage, current and power dissipation. Example Stress Ratio for a resistor;
Stress Ratio = Operating Power / Rated Power
Stud Mount. A type of package which provides a method of readily attaching one surface [the Stud] of the semiconductor device to a heat dissipater [heat sink] to achieve thermal management of the case temperature. A TO-61 is an example of a Stud Mount case. Other terms used to describe a Stud Mount device include Screw Mount, Bolt Mount, Chassis Mount or Panel Mount package.
Tab Mount. A type of package which provides a method of readily attaching one surface [the tab] of the semiconductor device to a heat dissipater [heat sink] to achieve thermal management of the case temperature. A TO-254 is an example of a Tab Mount case.
Temperature coefficient. The ratio of the change in a parameter to the change in temperature.
Thermal Derating. Reducing a transistor maximum operation based on thermal considerations.
Thermal Impedance. See Thermal Impedance Definition.
Thermal resistance. Thermal resistance is the temperature rise, per unit power dissipation, of a junction
above the temperature of a stated external reference point under conditions of thermal equilibrium. Thermal resistance graphs are also commonly provided with transistor data sheets. Thermal resistance is defined as Roja [the 'o' is theta].
Thermal resistance defines how well a material can
resist the flow of heat. A figure of merit for heat transfer [temperature drop divided by power dissipation] between different points in a conductive system. (T1 - T2)/Pd [in C/W].
For typical semiconductor thermal management
applications, low thermal resistance is desired. The total Thermal resistance of a device is the Junction-to-Case Resistance which is what is provided for in the derating curves. However, when a heat sink is applied to a device the total Thermal resistance becomes the device's Junction-to-Case Resistance plus the Case-to-Heatsink resistance plus the heatsink-to-ambient resistance. In many cases a heat sinks data sheet will provide surface to ambient thermal resistance for the heat sink.
Thermal Runaway. A heat related condition within a transistor or some other semiconductor device. As a transistor heats up electrical characteristics within the transistor cause increased losses within the transistor causing additional heat, which then increase losses still more. As the transistor continues to generator more and more heat the losses grow [runaway] until the junction temperature is exceeded and the transistor is destroyed. Thermal Runaway is provided in many of the charts above.
