modified 2 years ago

Question..

00:36:44

What's the difference between these two setups? Would u use one over the other?

published 2 years ago

592azy2circuitdude

2 years ago

Hi. Maybe I can help. It looks to me that the only difference between the two setups is that the Collector and Emitter terminals are switched.

592azy2circuitdude

2 years ago

The transistor on the left is in the Active Region. This is the standard way transistors are biased. The small current flowing out of the Base controls the large current through the Collector.

592azy2circuitdude

2 years ago

The transistor on the right is in the Reverse Active Region, which is hardly used (if at all). The disadvantage is that the transistor no larger uses the Base current to control the Collector current. The Base current is very high and just splits between Emitter and Base terminals. You have less control with this configuration.

sicarus

2 years ago

Thank you very much for the great answer! You say "hardly used".... could you think of an example of when you would use something like that?

592azy2circuitdude

2 years ago

Reverse Active is just like Active, but everything is reversed. Since BJTs are not symmetrical (Emmiter and Collector terminals have different characteristics), operating in reverse kinda works, but not very well. That's why it's not used. HOWEVER, I found online that some TTL chips used Reverse Active Mode to create better transistor switches, much like your circuit demonstrates!

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