2N2906 Transistor Derating Curves

2N2906 Through Hole Version

2N2906A Temperature-Power Derating Curve [2N2907A]
PNP General Purpose Silicon Transistor. Package, TO-18 metal Can.
2N2906A Applications; High-speed switching, Driver applications for industrial service ... NPN complements: 2N2222 and 2N2222A devices

2N2906 Transistor Temperature-Power Derating Curve
2N2906 Transistor Temperature Derating Curves

The above chart details the maximum allowable power dissipation with increasing ambient temperature. Maximum operational power dissipation is achievable at 250C. However above 25C the maximum package dissipation must be reduce to insure that the devices junction temperature remains constant. Decreasing a devices operational limits as temperature is increased is called derating. This graph details a 2N2906 transistor in a TO-18 metal package [through-hole].

The graph shows maximum operational wattage in still air [free air], using forced air cooling will allow the 2N2906A to operate at a higher temperature with out derating the power. Attaching a clip-on heat sink will also allow the transistor to operate at higher temperatures. Of course power derating is never required if the device is operated under its maximum limits.

Refer to MIL-PRF-19500/291; Semiconductor Device, Transistor, PNP, Silicon, Switching, Types 2N2906A, 2N2906AL, 2N2907A, 2N2907AL, 2N2906AUA, 2N2907AUA, 2N2906AUB, 2N2906AUBC, 2N2907AUB, and 2N2907AUBC, JAN level, [TO-18 package]
Note that the current version is the A version, and the specification references the 2N2906A version. However it's common just to refer to the transistors as 2N2906.

2N2906 Maximum Ratings:
Collector Emitter Voltage = 60 volts dc [Vceo]
Collector Base Voltage = 60 volts dc [Vcbo]
Emitter Base Voltage = 5 volts dc [Vebo]
Collector Current = 600mA [Ic]
Power Dissipation 250C = 400mW
Operating Junction Temperature = -65 to +2000C [Tj]
Storage Temperature = -65 to +2000C [Tstg]

How to interpret the graph;
The top curve [right-most] represents the maximum permissible operating range of the 2N2906. At no time should the junction temperature of the 2N2906 exceed 200C. The next curve shows the desire operating range of the 2N2906 for a junction temperature of 150C. However to provide for a longer life most designs will elect to operate a either 125C or 110C to provide even more head-room.

Select the desired junction temperature [below 200C]. Draw a line parallel to one of the curves to determine the functional operation of the 2N2906 over temperature.

Heat Sink Manufacturers [Clip-on], Fan Manufacturers

Similar device; PN2906 in a TO-92 case [non-metal package]
Although heat sinks are available for plastic packages, they are not very efficient.

2N2906 Surface Mount Version

There are two surface mount version defined in the specification, a UA version [below] and a UB version [left]. Both surface mount versions have a higher power dissipation over temperature than the through-hole version in the TO-18 package. The Surface Mount Devices [SMD] defined in the military specification are ceramic packages with a metal lid, and not the normal plastic SOT-23 packages normally used with low-power SMD transistors.

UA SMD Graphic and Schematic
2N2906-UA Package Style and Case Pinout

Attaching a heat sink to the metal lid of either of the surface mount versions will even greater heat to be dissipated, than the power dissipated from the device with out a heat sink. One version of a heat sink is shown to the right. A horizontal mounted heat sink is shown with straight fins, but other fin shapes are possible. Of course different size heat sinks are also available. Normally the heat sink will be black anodized aluminum. The heat sink can be attached by epoxy to the top of the 2N2906. Refer to the list of manufacturers producing Thermal Adhesive Compounds for use with heat sinks, that could be used with this type of heatsink.

Surface Mount version of a metal Fin Heat Sink

With out showing the derating graph, both SMD transistors have the same four curves as shown above. However the difference with the SMD types is that the data is related to the temperature of the Printed Wiring Board [PWB] solder pad, and not the temperature of the surrounding air as depicted in the curve above. Decreasing a device or components operational limits as temperature is increased is called derating, in this case derating a devices operational power dissipation vs copper pad temperature. Note that for what ever reason the chart does not provide the size of the solder pad used to attach the component [or the weight of the copper]. The fact that the acural solder pad or attachment point is not giving in detail, because the solder pad should act as a heat sink, making the size of the pad relevant to the amount of heat the component could handle.

The 2N2906-UA has a maximum junction temperature rating of 1 watt up to 90 degrees centigrade, and than falls in a straight line down to 200C. The maximum power dissipation of the 2M2906A-UB version is 1.5 watts out to 140C falling in a straight line down to 200C. The middle curve which defines the point that any electrical tests are performed is ignored here. The two gray curves which define the optimal power dissipation over temperature are as follows.

The 2N2906AUA should be operated between 0.8 and 0.9 watts at 25 C, moving down to zero watts between 110C and 125C. The 2N2906AUB operates a bit higher, having a power rating of 1.5 watts out to between 50C and 70C, than falling to zero power between 110C and 125C.

TO-18 Stright Fin Collar Heat Sink
2N2906 Heatsink

TO-18 metal Package
TO-18 metal Can Transistor

Lead 1= emitter, lead 2= base, lead 3= collector

Related: PNP GP Transistor
2N2906A [thru-hole]
2N2906AUA [SMD]
2N2906AUB [SMD]
Transistor Derating Curves

How to Derate;
Component Derating Guidelines

List of Transistor Manufacturers

Use short leads with the TO-18 package
to conduct heat into the PWB.
Avoid a transistor socket if possible.

Engineering Phrases:
2N2906 Transistor reliability,
2N2906 Failure rate
Qualified Military 2N2906, TO-18

UB Surface Mount Package
Transistor Package, 2N2906-UB SMD

Editor Note
Example heatsinks are provided
on many of the derating topics,
For the different package types.

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Modified 1/21/12
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