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Electricity section 4: 4.4 The diode electrical device - how does it work and what is it used for?

Doc Brown's Physics exam study revision notes

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4.4 The diode electrical device - how does it work and what is it used for?

See also Part 3.4 An experimental investigation of I-V characteristics of a diode

graph of current versus p.d. volts for a diode

The current through a diode flows in one direction only

This is because a diode has a very high resistance in the reverse direction.

A diode is a special device made from a semiconducting material based on silicon (classed as a semi-conductor).

Since the current only flows one way through a diode, it can be used to convert an ac current into a dc current (rectifier, rectification).

With alternating current (ac), the current changes direction in a cycle, but with direct current (dc) there is no reversal in current direction, it flows one way with a constant voltage.

Oscilloscope traces comparing ac and dc current signals - showing the alternating + <=> - oscillation of the alternating current p.d. and the constant p.d. of a direct current.

Diagram 2. shows what happens if pass an ac current through a diode - 'before and after' trace after the dc output has been smoothed.

In some devices in the home the output from e.g. the transformer in your computer power supply, is rectified to convert it from ac to a dc supply.

Uses of a diode

Diodes are used as rectifiers (converting an ac signal/current to dc), signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators etc. etc. in other words - rather useful in electronic circuits.

Diodes are used radio transmitters and receivers.

See also Part 3.4 Investigating the current - voltage characteristics of a diode - graph explained

 

INDEX for physics notes on testing circuit devices and how they used


Keywords, phrases and learning objectives for a diode device in an electrical circuit

Know how a simples diode circuit device work,

Be able to describe what is diodes are used for e.g. rectifies a.c. to d.c., signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators and oscillators.


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