Confusing rating in Fairchild datasheet of KSP10

Thread Starter


Joined Nov 13, 2015
The derate parameter in the datasheet of KSP10 transistor has 8.0 watts per degree celsius. 8 WATTS?! :oops:
Maybe it should be 8.0 mW instead. Am I right?

Another: The power dissipation rating of the KSP10 (TO-92) UHF transistor looks a little bit high. Does this mean the transistor is a little bit high in power than general TO-92 UHF signal transistors?
Thank you!


Last edited:


Joined Aug 7, 2020
It does look a bit of a mess.
There seems to be two entries for power rating, but one is for ambient temperature and one is for case temperature.
Unless you are using a heatsink the case temperature line isn't of any interest.


Joined Aug 21, 2008
@Bordodynov has once again provided THE valuable solution.

You have spotted what is clearly an error in the datasheet. The KSP10 is for low power operation. Basically (and I think you already know this) anything in a TO-92 is not going to deliver much power, at least on a continuous basis. It is good for small signal generation and processing into the hundreds of MHz. Seems it would be useful as a local oscillator, mixer, or detector for RF.

The key factors for not exceeding the die temperature are the power dissipation, the thermal resistance from the junction to ambient, the maximum junction temperature (be sure to derate -stay well below that temperature) and the expected maximum ambient temperature.

Minor detail: The thermal resistance from junction to ambient increases as altitude increases (air pressure decreases).

Thanks to your post, this is the first time I noticed that the base-emitter junction reverse breakdown occurs after 3 volts, half of what most small signal transistors can withstand. There must be some interesting way to put this to use.