|
Fig : A |
Transistors are manufactured in different shapes but they have three leads (legs).
The BASE - which is the lead responsible for activating the transistor.
The COLLECTOR - which is the positive lead.
The EMITTER - which is the negative lead.
The diagram below shows the symbol of an NPN transistor. They are not always set out as shown in the diagrams to the left and right, although the ‘tab’ on the type shown to the left is usually next to the ‘emitter’.
|
Fig :B |
Diagram 'A' shows an NPN transistor which is often used as a type of switch. A small current or voltage at the base allows a larger voltage to flow through the other two leads (from the collector to the emitter).
The circuit shown in diagram B is based on an NPN transistor. When the switch is pressed a current passes through the resistor into the base of the transistor. The transistor then allows current to flow from the +9 volts to the 0vs, and the lamp comes on.
The transistor has to receive a voltage at its ‘base’ and until this happens the lamp does not light.
The resistor is present to protect the transistor as they can be damaged easily by too high a voltage / current. Transistors are an essential component in many circuits and are sometimes used to amplify a signal.
|