Datasheet confusion

"Rikard Bosnjakovic"

** No you do not - they are not data sheets. ** Those are second party re-listings.

Likely compiled by 12 year old Mexicans.

** Original manufacturers data sheets for individual types are there if you bother to look.

Shame YOU are too damn lazy to feed a number into Google.

** For the same type number in the exact same package - there is no significant variation in Pd.

...... Phil

The 3906 is a small signal transistor. It is not meant to dissipate any significant power. If you keep the dissipation below a couple of hundred milliwatts you should be ok. If you are asking about 650mW, you are using the WRONG part regardless of what some data sheets may say. Be safe and do not exceed the lowest listed value regardless of manufacturer. If you need more power, pick a different part.

Neither of those compilations is actually a data sheet. They are collections of interpretations of the information from data sheets. The first gives a power limit and the conditions that apply to that limit (25 C ambient). the second gives a power limit but no conditions, so it may apply to a completely different situation, like maximum rated ambient temperature.

These compilations are handy to find somewhat similarly rated devices, to start a selection process (for anything with more at stake than a hobby project), but the final decision should always include looking at the actual manufacturer's data sheet, and reading all the fine print. The same specification often means different things when you take the notes and specified test conditions into account.

The universe is complicated. Sorry.