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I'm coming to electronic from sw side so I have holes in my e-knowledge... please help solve this situation. I have an MCU pin connected to a BC327 pnp base through an 1K resistor. I wish to switch the power of something else with that. The emitter of transistor connected to +5V. The collector is not connected to anywhere yet. When I pull the MCU pin to 0V base gets low and the transistor gives +5V on its collector - it is what I expected. When I pull up to +5V the MCU pin (and therefore the base) I can measure about -10V at the collector of the transistor relative to the 0V. Ups, it's not what I expected. I expected 0V. I'm afraid of damaging the whole stuff and I don't dare to make more experimentations. So my questions are: - is it normal when collector is not connected to anywhere? - is it refers to a damaged transistor potentially? - if the answers to the above questions were "no" what else can cause this symptom?

Thanks in advance, F

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It's not normal. When the transistor is 'off' it is effectively an open circuit save for a bit of leakage to the +5V rail. A normal meter provides a an resistance of maybe 10M or 10G+ in some cases to the 0V rail. In any case, the voltage should be between 0V and 5V (and most likely close to 0V).

If you have a negative supply somewhere in your circuit, maybe there is a resistance between that and the PNP collector, if not then maybe something is up with your meter- it should read 0V when the test leads are open.

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