Diodes and rectification

With most electricity generated to have alternating current, it is useful in some cases for this to be converted into direct current. This process is called rectification.

At its heart is the diode, an electrical component that only conducts electricity in one direction.


Key Concepts

Diode

A diode is an electronical component that conducts current in one direction (forward bias).

An ideal diode would have zero resistance in one direction and infinite) resistance in the other.

Stages in rectification

Half wave

The simplest form of rectification is the insertion of a diode in the series circuit. All current in the forward direction is transmitted; no current flows in reverse bias.

Notice that the diode symbol acts as an arrow to show the direction in which conventional current will flow.

This circuit has the downside that current is only flowing for half of the time.

Full wave

Full wave rectification uses two diode pathways (in opposite directions) to enable the current to flow at all times. Each diode path runs through the same resistor (or desired electrical component).

See if you can trace a finger around the following circuit diagram, first starting upwards from the power supply and then downwards.

While an improvement on half wave rectification, the output is still sinusoidal in magnitude.

Essentials

Semiconductors

Most diodes are made from semiconducting materials such as silicon.

Diode bias

The diode forward and reverse biases come from a PN junction connected to two electrical terminals.

Wheatstone bridge circuit

An understanding of rectification circuit diagrams can also be used to determine unknown values. The following circuit is known as a Wheatstone Bridge; the current directions are arbitrary.

\(R_1\) and \(R_3\) are known fixed resistors. \(R_2\) is adjusted until \(V_G\) is zero, at which point there is no net current from D to B. \(R_\text{x}\) can be determined:

\(R_1+R_2=R_3+R_\text{x}\)

Test Yourself

Use quizzes to practise application of theory.


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