modified 10 years ago

Question

01:01:19

What is the difference exept that the base needs more current? I can't see a big difference

published 10 years ago

ferlop

10 years ago

As you can see on the circuits,the current thru the load is different with everything else being the same. The NPN transistor can carry more current than the PNP transistor. And it can do that because the NPN the electrons are the current carrier, and on the PNP the holes are the current carrier. Also hole carriers are a bit slower that electron carriers. You might think there is not a big difference because it's only 3.43 ma of load difference, but that might be enough to decide which transistor to use for a certain application.

thebugger

10 years ago

Both of them are NPN's but the lower one is connected correctly. The current must come through the collector and exit through the emitter, with no exception. This way the transistor is in oversaturation mode and won't have an amplifying effect. As you can see the upper one (which is the correct one) draws very low current from the base bias supply. The wrongly placed transistor draws as much current from the base supply, as it does from the collector, which means there isn't any amplification present.

ferlop

10 years ago

He got me, I didn't pay attention and assumed a NPN and a PNP, good catch thebugger. so may explanation is for two different transistors and not for this set up, disregard.

hunar

10 years ago

You mean that i can't make radio transmitters without finding the correct pin?

WTFCircuit

10 years ago

Yes

ferlop

10 years ago

But isn't one transmitter going to be more efficient than the other when the collector and emitters are reversed , besides having to much base current will overheat the transistor, correct?

thebugger

10 years ago

You can't have a transmitter without an active device like a transistor. But when the transistor is not wired correctly it doesn't provide any amplification, therefore it isn't an amplifying component anymore. The transistor is a 3 terminal component and all 3 terminals MUST be wired correctly for it to work properly. There are a few applications where they're wired differently but let's not dwell right now.

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