Transistor Schematic Symbols Quiz

Electronic Schematic Symbols: Understanding Transistors

Electronic schematics are visual representations of circuits used by engineers and technicians to design, analyze, manufacture, and troubleshoot electronic systems. These symbols can vary between different organizations and even within the same organization. However, there is some consistency in their usage throughout the industry, and certain standards have been established for various sectors. In this article, we will focus on one of these components - the transistor.

A transistor is a three-terminal electronic device commonly used to amplify or switch electronic signals and electrical power. It has two main types: bipolar junction transistors (BJT) and field-effect transistors (FET). Both types operate based on the principle of amplification and switching functions.

Bipolar Junction Transistors (BJT)

The bipolar junction transistor (BJT) was invented by William Shockley in 1946. It consists of alternating layers of p-type and n-type semiconductors. There are two basic configurations for a BJT: NPN and PNP.

NPN Transistor

The NPN transistor is formed by joining two p-type regions together with an n-type region sandwiched in-between. The base-emitter junction operates like a diode and controls current flow from emitter to collector while the collector-base junction acts as another diode that blocks current from collector to base.

PNP Transistor

The PNP transistor is constructed similarly but with the roles of p and n reversed compared to the NPN transistor. Here, the base-collector junction behaves like a diode and conducts current when reverse-biased, allowing it to turn on. Meanwhile, the collector-emitter junction also acts like a diode which blocks current under normal operation.

Transistors are typically drawn schematically as follows:

      +-------+
     |       |
+--Emitt|   B  | C---
er    |   E  |   oll
-----+-----+

Here, E represents the emitter, B is the base, and C stands for the collector.

Field-Effect Transistors (FET)

Unlike BJTs, field-effect transistors (FET) do not have a third voltage control terminal. Instead, they rely on an electric field to control the flow of charge carriers. FETs come in two varieties: junction gate FETs and insulated gate FETs.

Junction Gate FETs (JFET)

In junction gate FETs, current flows through a channel amidst two heavily doped regions called the source and drain. This channel leads to a pn junction known as the gate, which serves as a voltage-controlled resistive element. As the gate voltage changes, the width of the conducting channel alters, thus controlling the amount of current flowing in the circuit.

Insulated Gate FETs (IGFET)

There are two types of insulated gate FETs: MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and JUSFETs (Junctionless Unity Gain IGFETs). These devices operate analogously to JFETs, except they utilize metal gates that are surrounded by thick oxide layers to isolate them from the channel's surrounding space-charge region.

An example of an FET schematic symbol is as follows:

      +-------+
     |       |
S---Drain|---Gate|---Source

Where Drain is the drain, Gate is the gate, and Source represents the source.

Understanding the schematic symbols of electronics such as transistors is crucial for designing, manufacturing, and maintaining electronic systems. By familiarizing yourself with these symbols, you're equipped with valuable knowledge that can help you navigate through complex circuit diagrams and effectively communicate your ideas to others within the field.