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Base-Emitter Resistance greater than Collector-Base Resistance NPN

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Wond3rboy

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Hi, this time the question is pretty simple and straight forward :p I wanted to know the reason why is the resistance of the B-E junction greater than that of the C-B junction for an NPN Transistor.
 
The base-emitter of a transistor is not a resistor, instead it is a diode. It is driven with a small current.

The collector to base of a transistor is another diode, not a resistor. It is usually reverse-biased so it does not conduct.

The transistor amplifies the base-emitter current which produces a much higher current from collector to emitter.
 
Thanks for the reply AG. Sorry i mixed up the diode function's unit. It should be volts, when put on the diode function, the B-E diode shows a higher voltage than the B-C junction. Is there any special reason for that ? Or its just a constructional consideration.
 
The emitter-base diode is different to the collector-base diode.
Why are you measuring the forward-biased voltage of the collector-base diode when normally it is never forward-biased?
If you need to see which pin is the emitter and which pin is the collector then simply look at its datasheet.
 
Thanks for the Reply AG. I do look up the datasheet for the pin configuration, i was just inquisitive about any specific reason. Guess its a constructional consideration. Thanks again.
 
Hi,

You can look at the transistor sort of like two diodes with one common junction. That common junction changes the behavior from simple diodes to a transistor. However, when you bias the junctions individually one at a time like you did (and this is a common practice just to perform a quick check on the transistor) you can look at it as two separate and distinct diodes. When you look at it in this light, you see two diodes that are constructed somewhat differently and this means their operating parameter values are different. For example, the emission constant is usually different for both diodes as well as the saturation current. The result is that for the same forward test current each diode will measure a different forward voltage.

Im sure you already know that to perform a better test you should test it with a forward base emitter current and a reverse base collector voltage.
 
Yep. I do check my transistors that way, but this is for some students that i was giving a demo to. Told them it is most probably a construction thing but wanted to confirm.
 
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