Transistor Derating Recommendations based on a linear equation.

Unlike the guidelines in this section, Transistor Derating Curves are not provided.

Most data sheets only provide an equation without a chart.

**Transistor Failure Rate**

These design recommendations are for devices in still air, with no other near-by devices generating heat. So the recommendations do not account for a device enclosed in a chassis or next to other transistors on the Printed Wiring Board [PWB]. So in the final design these number may not achieve the design goal of keeping the junction temperature under its maximum number [depending on the individual transistor].

As a general guideline use the Derating Factor shown to the left of the part number.

The derating factor may apply to one or more packages, using the same semiconductor.

2N918, TO-72 metal can, Derate linearly above 25C, 1.14 mW/^{0}C

2N1893, TO-5 metal can, Derate linearly above 25C, 17.2 mW/^{0}C

2N2060, TO-77 metal can, Derate linearly above 25C, 12.1 mW/^{0}C

2N2369, TO-18 metal can, Derate linearly above 25C, 2.06 mW/^{0}C

2N2605, TO-46 metal can, Derate linearly above 25C, 2.28 mW/^{0}C

2N2857, TO-72 metal can, Derate linearly above 25C, 1.71 mW/^{0}C

2N2905, TO-39 metal can, Derate linearly above 25C, 17.2 mW/^{0}C

2N2907, TO-18 metal can, Derate linearly above 25C, 3.08 mW/^{0}C

2N2919, TO-78 metal can, Derate linearly above 25C, 7.14 mW/^{0}C

2N2920, TO-78 metal can, Derate linearly above 25C, 7.14 mW/^{0}C

2N3057, TO-46 metal can, Derate linearly above 25C, 10.3 mW/^{0}C

2N3227, TO-18 metal can, Derate linearly above 25C, 2.06 mW/^{0}C

2N3486, PNP, TO-46 metal can, Derate linearly above 25C, 11.43 mW/^{0}C

2N3499, NPN, TO-39 metal can, Derate linearly above 25C, 5.71 mW/^{0}C

2N3500, NPN, TO-39 metal can, Derate linearly above 25C, 5.71 mW/^{0}C

2N3501, NPN, TO-39 package, Derate linearly above 25C, 5.71 mW/^{0}C

2N3506A, NPN, TO-39 package, Derate linearly above 25C, 28.6 mW/^{0}C

2N3507, NPN, TO-39 package, Derate linearly above 25C, 5.71 mW/^{0}C

2N3700, NPN, TO-18 package, Derate linearly above 25C, 3.08 mW/^{0}C

2N3735, TO-39 metal Can, Derate linearly above 25C, 16.6 mW/C

2N3737, TO-46 metal Can, Derate linearly above 25C, 11.3 mW/C

2N3810, TO-78 metal Can, Derate linearly above 25C, 3.43 mW/C

2N3811, TO-78 metal Can, Derate linearly above 25C, 3.43 mW/C

2N3866, TO-39 metal Can, Derate linearly above 25C, 16.6 mW/C

2N3904, TO-92, SOT-23, SOT-223, Derate linearly above 25C, 5 mW/C

2N3960, TO-18 metal Can, Derate linearly above 25C, 2.3 mW/C

2N3996, Stud-Mount, Derate linearly above 25C, 11.4 mW/C

2N3997, Stud-Mount, Derate linearly above 25C, 11.4 mW/C

2N3998, Bolt-Mount, Derate linearly above 25C, 11.4 mW/C

2N3999, Bolt-Mount, Derate linearly above 25C, 11.4 mW/C

2N4029, TO-18 metal Can, Derate linearly above 37.5C, 3.08 mW/C

2N4449, TBD package, Derate linearly 6.85 mW/^{0}C above TC = +25^{0}C

2N6674, 2N6675 TO-3 package, Derate linearly 34.2 mW/^{0}C above TC = +25^{0}C

2N6689, 2N6690 TO-61 package, Derate linearly 17.1 mW/^{0}C above TC = +25^{0}C

2N7367 IGBT, TO-258 package, Derate linearly 1.56 W/^{0}C above TC = +25^{0}C

2N7368 IGBT, TO-259 package, Derate linearly 1.56 W/^{0}C above TC = +25^{0}C

2N7508U3, TO-276AA package, Derate linearly 0.6 mW/^{0}C above TC = +25^{0}C

2N758xT3, TO-254AA package Derate linearly 1.67 W/^{0}C above TC = +25^{0}C

[2N7580T3, 2N7582T3, 2N7584T3, 2N7585T3, & 2N7580T3 in a TO-254AA package].

2N7625T3, TO-257AA package, Derate linearly 0.6 mW/^{0}C above TC = +25^{0}C

Attach a Heat Sink to the components tab for higher temperature operation.

Otherwise follow the recommendations in the curve or consult the data sheet.

For a general Rule-of-Thumb recommendation follow this Dearating Factor

**Transistor Stress Ratio** = Operating Power / Rated Power = 75%.

Engineering best practices indicate that all designs should be derated for temperature.

Which means a design should never force a device to operate at its maximum power dissipation [on near its maximum power dissipation, without leaving some operating room].

A circuit design should also never force a semiconductor to operate at or near its maximum junction temperature.

Pushing the device up to its dissipation limits causes the semiconductor junction to heat up.

The problem is compounded as either the package temperature increases or the surrounding air temperature is increased. In general the life of a component [transistor in this case] reduces as the component temperature is increased [junction temperature].