I was looking at the datasheet for the 2n2222 transistor. Collector-Base and Collector-Emitter Breakdown Voltage is a bad thing from what I understand.

But is Emitter-base breakdown voltage good? Is the what causes the trasistor to "switch on". Or is Emitter Base breakdown with electricity flows backwards through the emitter to the base and "fries" it?

 

The breakdown voltages of a transistor are all "a bad thing." They are voltages that cause the transistor to breakdown or cease normal operation.

The voltage that causes the transistor to "switch on" is V(be), where the base voltage is higher than the emitter voltage, typically around 0.6V. The emitter-base breakdown would be V(eb), where the junction is reverse biased with the emitter voltage higher than the base voltage.

 

One of the breakdown voltages is a zener action, so I'm told. Never used it, but it is worth knowing (and I don't).

 

One of the breakdown voltages is a zener action, so I'm told. Never used it, but it is worth knowing (and I don't).

I think you know more than you are saying. Perhaps your point is that breakdown is not always a "bad" thing. The zener and avalanche breakdown effects need not be destructive, and have uses in zener diodes, avalanche transistors and avalanche photodiodes.

 

A transistor's emitter-base junction is small and is not connected to the transistor's case. When it has avalanche breakdown then the heat is concentrated and slowly reduces the hFE of the transistor.

A Zener diode has a huge junction and is welded to heat-conducting connecting wires. It is designed to have avalanche breakdown.