Transistors

Basics of Transistors

  • Transistors are essential semiconductor devices that can be used as either a switch or an amplifier.
  • They are typically composed of semiconductor material such as silicon or germanium.
  • A transistor consists of three layers of N and P-type semiconductor materials. The three-layer configuration can be either NPN or PNP.
  • The three parts of a transistor are the emitter, the base, and the collector.

Characteristics of Transistors

  • The layer at the middle, or the base, is thin compared to the emitter and collector.
  • In an NPN transistor, the emitter is N-type, the base is P-type and the collector is N-type. In a PNP transistor, the emitter is P-type, the base is N-type and the collector is P-type.
  • Transistors exhibit the property of current gain or amplification. The small input current at the base can control a much larger current flow from the collector to emitter.
  • The I-V characteristics of a transistor represent the relationship between the input current and the output voltage.

Types of Transistors

  • Bipolar Junction Transistors (BJT) are the transistors that we’ve described so far with a three-layer NPN or PNP configuration.
  • Field Effect Transistors (FET) control current by varying the width of a channel along which charge carriers move.
  • Metal Oxide Semiconductor Field Effect Transistors (MOSFET) are commonly used in integrated circuit technology.

Applications of Transistors

  • Transistors are fundamental in amplification circuits which are used in almost all electronic audio devices.
  • Utilised in switching circuits, transistors can turn electrical signals or power to a load on or off.
  • Transistors are also vital components in oscillator circuits, which are used for generating waveforms for radio signals and other applications.

Special Mention: Transistor Limitations

  • The maximum power dissipation of a transistor is the maximum amount of power it can handle without damaging itself.
  • The maximum frequency of operation refers to the upper limit of frequency that the transistor can amplify a signal effectively.
  • The base-emitter voltage, Vbe, must exceed a specific threshold (usually around 0.7V for silicon) for the transistor to turn on and conduct properly.

Remember: Understanding of both technical aspects of transistors and their practical applications is crucial. Always consult the datasheet for specifics of a transistor for its right utilisation in a circuit.