I'm a bit curious about this thing. I know in NPN BJT transistor, current flows from collector to emitter since the emitter usually connected to the ground (please correct me if I'm wrong). What I want to ask is, in the worst case (assuming severe transistor failure,) is it possible for current to flow from emitter to collector(assuming that the collector have lower potential or connected to ground) and the emitter have higher potential compared to the collector?
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\$\begingroup\$ FYI: Saying "ground" only complicates your question. A transistor doesn't know what "ground" is. All you need to ask is, "Can current flow from emitter to collector?" Andy Aka's answer says, "Yes, it can." \$\endgroup\$– Solomon SlowCommented Jun 28, 2021 at 11:23
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in the worst case (assuming severe transistor failure), is it possible for current to flow from emitter to collector
You don't need to assume transistor failure for this to happen. If you swap emitter and collector terminals, you will get an operational device but, it's β will not be as high as a normal connection. However, it will saturate to a lower emitter-collector voltage when driven hard and, occasionally, I've seen engineers do this (despite it looking a little odd).
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\$\begingroup\$ I see, thanks for the answer! \$\endgroup\$ Commented Jun 28, 2021 at 7:15
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\$\begingroup\$ to prevent this event, can i simply add a diode or does there exist other component to do such? \$\endgroup\$ Commented Jun 28, 2021 at 7:18
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\$\begingroup\$ Like Andy writes: "You don't need to assume transistor failure for this to happen" so there's nothing you need to do to "solve" this as it will not be an issue provided you use the transistor properly (not exceed its maximum ratings). There is nothing to "solve" so don't try to! (Don't worry, it is typical for beginners to try and solve all kinds of non-issues.) \$\endgroup\$ Commented Jun 28, 2021 at 7:22
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1\$\begingroup\$ @AgustinusYudhistira You need to be totally clear about your circuit and explain what it is intended to do. I cannot mind-read on Mondays. \$\endgroup\$– Andy akaCommented Jun 28, 2021 at 7:22
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1\$\begingroup\$ No, I don't have any suggestion and we have drifted far away from your original question now so, I suggest you raise a new question and get others involved in suggesting a solution @AgustinusYudhistira - this is a Q and A site and not a teaching forum; you ask a question and somebody answers it. OK a little leeway is given for follow-up questions but, we have gone past this point now . \$\endgroup\$– Andy akaCommented Jun 28, 2021 at 9:20