Fried Transistor...

[JacobEdward]

This is the datasheet https://www.fairchildsemi.com/datasheets/2n/2n3906.pdf

The maximum voltage rating for the collector is suppose to be 40V and it fried from a 17V source... also the switch completely broke down... am I reading this right?  You control the transistor with a 5V signal and the collector/emittor at most 40V?  I've attached a screen shot of the specific part of the data sheet I'm reading

[xrunner]

Well, you say "control it with a 5V signal" but you really turn it on with a small current. It can come from a 5V supply, but you need a resistor to drop a lot of that voltage so the transistor turns on with a small current. It may have pulled too much current even if it was connected to a 17V supply - need more details of the circuit ...

[Seekonk]

If you drove something inductive like a relay, more than 40V can be generated.  The transistor figured out exactly what it was supposed to do, short out.  Post a circuit and we will figure where things went wrong.

[sleemanj]

The 3906 is a PNP transistor.

The Collector to Emitter junction as a breakdown of negative 40v in the off condition, that is for example the collector at 40v and the emitter at 0v, or the emitter at 17v and the connector at 57v, etc..

The 40v is telling you just how much "reverse" voltage across the transistor it can stop, just like a diode's reverse breakdown voltage.

The Base to Emitter junction can withstand 5v, in the off condition that is, the base can be 5v and the emitter can be 0v (or 10v and 5v, or ....).  Remember this is a PNP, if the BASE is (close, equal or) higher than the Emitter then the transistor is OFF.   Remember the emitter to base is effectively a diode, this is telling you that this diode can withstand up to 5v reverse biasing.  In other words 5v figure is telling you, in a way, just how "hard" you can "push" it into the off region.

Remember it's a PNP, you "pull" the base down lower than the emitter (by way of an appropriate current selection, this is a BJT not a FET), to turn on, and "push" it up to the emitter to turn it off.

Post your circuit diagram.

[Zero999]

A schematic would help.

There are plenty of ways to blow up a transistor, other than overvoltage.