Power Transistor Basics

• Transistors amplify and switch current. Jupiterimages/Photos.com/Getty Images

  Transistors are a type of semiconductor used for a wide variety of electronics. Transistors are small and easily placed in nearly any circuit and have several universal applications. Sometimes rows of transistors are used to control electrical flow in more complicated systems. Large transistor groups produce a large amount of heat and often need a heat sink to properly work.

Amplification

• One primary job of a transistor is to amplify a current. This occurs when the incoming current does not have enough voltage to power a device. If the incoming current is only three volts, the transistor might be able to increase it to three or fours times the voltage, enough to adequately power the device. This is why it is called a transistor (trans = change) rather than a resistor, which resists and lowers the incoming current.

Three Parts

• Transistors are made from a base, a collector and an emitter. The base activates the transistor and is the portion that can be either opened or closed (although the base generally lets a slight amount of current through no matter what). The collector acts as the positive lead and usually powers the device, while the emitter acts as the negative lead.

Switching

• Transistors are also used for switching power on and off from a device. When the input to the base of the transistor is zero or low, no base current flows, and the transistor is technically off. When current increases, the transistor allows the current to build inside before allowing it to flow from the collector side. This is a complicated process and changes based on the type of transistor and the arrangement of the circuit.

Materials

• Transistors typically are made of silicon and come in NPN and PNP designs -- N layers being negative and P layers positive. The most common type of transistor is NPN because it is easier and less expensive to make from silicon materials.