# Basic operation of BJT (Bipolar Junction Transistor) [duplicate]

I've searched many references, but now I'm stuck. What I understand so far is that a transistor is made up from two diodes, and as far as I know, the function of diode is only allow a current flow from one direction (ideal diode).

I've looked at this diagram of transistors:

For PNP transistor: If I trigger the Base with some small current, Ib, how can the current from the Collector flow to the Emitter, if there's a diode there (in the Emitter)?

Same question with NPN transistor.

I'm stuck here....

• The two-diode model of a transistor simply doesn't work. Throw that book away. – Chu Feb 11 '17 at 13:32
• So, what's the diagram of the transistor? i've search google and have that – Anton Io Feb 11 '17 at 13:38
• Yeah, you should stop thinking of them as two diodes as that will probably just confuse you. They say this because transistors are physically constructed with a P-N-P or N-P-N configuration, but they are all together in one piece of silicon. You can't model that with two discrete diodes. Firstly you would have P-N-N-P (or N-P-P-N), but also there is a lead between each. An actual BJT has more complex physics going on in the base layer and between the junctions. It's hard to give a short explanation of 'basic' BJT operation. – AngeloQ Feb 11 '17 at 13:40
• There are three main modes (cut-off, active, saturation) and there are various properties for each. I think the Wiki article does a decent job explaining it, and there are lot's of other good resources online - just stop thinking of it as two diodes from a functional perspective. en.wikipedia.org/wiki/Bipolar_junction_transistor – AngeloQ Feb 11 '17 at 13:41
• The diagrams of the transistors are as you showed in your question (the top ones, not the diode representations). – AngeloQ Feb 11 '17 at 13:42