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One component which has been shown but not described is the diode or ‘rectifier’

The Diode
One component which has been shown but not described is the diode or ‘rectifier’.   This is a device which has a very high resistance to current flowing in one direction and a very low resistance to current flowing in the opposite direction.   The base/emitter junction of a transistor is effectively a diode and, at a push, can be used as such.   A proper diode is cheap to buy and has far greater voltage and current handling capacities than the base/emitter junction of a transistor.

Diodes are mainly made from one of two materials: germanium and silicon.   Germanium diodes are used with very small alternating currents such as radio signals coming from an aerial.   This is because a germanium diode needs only 0.2 Volts or so to carry a current while silicon needs 0.6 to 0.7 Volts (same as a silicon transistor base/emitter junction).   Germanium diodes (and transistors) are very sensitive to temperature change and so are normally restricted to low power circuits.   One very neat …

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