Electrical – Have I fried the transistor in this circuit


It was a germanium PNP transistor. I might've pressed the button too. I saw transistors used as capacitors that were connected like this, but they weren't germaniums. What current (if any) has flown through the transistor? According to the datasheet, the reverse collector current at VCB=20V is 5μA, reverse emitter current at VEB=2V is 50μA, VEBO=3V, for what it's worth.


simulate this circuit – Schematic created using CircuitLab

Best Answer

The theoretical max power dissipation inside the transistor can have been 43 milliwatts. That's the case if the BE reverse breakdown voltage happens to be 4,5 V. If you have the datasheet of the transistor, find the thermal resistance from junction to the free ambient. Multiply it by 43 mW and see how much the internals were hotter than your room. Datasheet can also tell the max. allowed internal dissipation in some usual ambient temperature like 25 degrees centigrade.

If 2N3904 gets 43 mW, it would be about 9 degrees centigrade hotter inside than the room. I do not believe a discrete germanium transistor is destroyed due 43 mW dissipation.

ADD: Not any more so sure. I just found that I have had germanium rf transistors which can stand about max. 80 mW internal dissipation and that's in collector, which is several times larger than the emitter.