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Is a transistor uses opposite polarity?
Indeed we know that transistors are differentiated in two big families, the PNP and the NPN. This difference not only requires the use of opposite polarity for the three electrodes (collector, base and emitter), but it allows to achieve a symmetrical way of operation, very useful in many circuits, as we will see below.
Does it matter which way a transistor goes?
Yes current can flow in both directions. An NPN transistor backwards is also an NPN. There will still be a reverse beta, however, the backwards NPN transistor won’t work as well as a correctly oriented one will. It’s not recommended.
Why does a transistor switch not care about polarity?
Your relay operates irrespective of polarity because it is a switch operated by electromagnetism. The relay does not care about the polarity (direction of current flow). When current is flowing, electromagnetism closes the contacts.
What’s the difference between a transistor and a NPN switch?
The equations for calculating the Base resistance, Collector current and voltages are exactly the same as for the previous NPN transistor switch. The difference this time is that we are switching power with a PNP transistor (sourcing current) instead of switching ground with an NPN transistor (sinking current).
When do you use a transistor as a switch?
When there is a good amount of voltage which is ~0.7V in between the emitter and the base edges, then the flow of voltage at the collector to emitter edge is zero. So, the transistor in this condition performs as a switch and the current that flows through the collector is considered as the transistor current.
Why are multiple transistors used in a bipolar transistor?
Sometimes the DC current gain of the bipolar transistor is too low to directly switch the load current or voltage, so multiple switching transistors are used. Here, one small input transistor is used to switch “ON” or “OFF” a much larger current handling output transistor.