Why don’t two diodes connected anode to anode (or cathode to cathode) function as PNP or NPN transistors?
Simple diodes are PN junctions that prevent electron flow in one direction through the negative charge and (some) transistors are PNP or NPN with two PN junctions so why cannot I use two diodes connected cathode to cathode or anode to anode (so that two anodes or two cathodes present on both sides) to replace a transistor/do not work that way?
Edit: Just reread the rules and it says that the question must be clear from the title (but I can’t change it) so I’ve put it on the first line.
In: 5
“Imagine a diode as a one-way door for electrons. It only lets them go in one direction. Now, a transistor is like a special gate with two doors. It can control the flow of electrons in a more complex way.
If you connect two diodes, like putting two one-way doors together, it won’t work like a transistor. That’s because the doors in a transistor can work together, one helping the other. But with two diodes, they can’t do this teamwork. It’s like having two doors, but they can’t work together to control the electron flow the way a transistor can. So, diodes connected this way can’t do the job of a transistor.”
Two diodes back to back are not PNP. It’s PN(Metal)NP. A semiconductor metal junction does not behave the same way as if the metal were not there.
Furthermore, the thickness and doping strength of each layer in a BJT is very specific. If you change those parameters, the transistor will perform very differently (or fail to perform). The PN junctions in diodes are tuned for different properties and applications.
There is more to a transistor, than just two PN junctions. The base must be thin – thinner than the mean charge travel distance, so the charges can randomly cross the base and get to the collector. The emitter is small, but heavily doped, so it contains more charge carriers. The collector is big, so it can catch more stray charges.
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