There are 20 milliamps flowing into the collector pin and 25 milliamps flowing out of the emitter. In this simplified example, when the switch is pressed, there are five milliamps flowing into the base pin. We can remove the main circuit and the control circuit Led will still turn on when the switch is pressed, but the current is returning to the battery through the transistor. On the control circuit we can see the current is flowing through both wires to the transistor. The main circuit is off until we press the switch. Both are connected to the positive of the battery. With an NPN transistor we have the main circuit and the control circuit. The entire thing is enclosed in a resin to protect the internal materials. In a PNP transistor this is just configured the opposite way. The base wire is connected to the P type layer. In an NPN transistor we have two layers of N Type material and one layer of P type. Inside the transistor we have the collector pin and the emitter pin between these. We can sandwich these together to form an NPN or a PNP transistor. We combine these materials to form the PN junction. Pure Silicon has almost no free electrons, so what engineers do is dope the Silicon with a small amount of another material which changes its electrical properties. So do check the manufacturer’s datasheet. However, not all transistors use this configuration. Typically with these resin body type transistors with the flat edge, the left pin is the emitter, the middle is the base, and the right side is the collector. This stands for the emitter, the base and the collector. Now, with a transistor we have three pins labelled E, B and C. The two transistors look nearly identical, so we need to cheque the part number to tell which is which. We have two main types of bipolar transistors, the NPN and the PNP type. Scroll to the bottom to watch the YouTube tutorial. What is the difference between an NPN and a PNP transistor.
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