DTM7000
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Doc.: 00293978-v1
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Diodes
They are members of the semi-conductor family and are used to let current flow in one direction whilst
blocking it in the other.
The graphical symbol used for the diode is:
The arrow shows the direction in which current may flow.
Current flows
Current cannot flow
The use of diodes is not restricted to electronic circuits, they can often be found in classical electrical
circuits (e.g.: alternators).
Zener diodes
Take a standard diode. If one applies too high a voltage in the opposite direction the diode will let current
pass, but this will damage it, rendering it unusable.
However, the Zener diode will permit voltages above a certain level to pass through it in the opposite
direction without breaking.
Symbol:
The Zener diode can be found in a wide range of circuits, notably for voltage regulation, load voltage
regulators, etc.
Transistors
Members of the semi-conductor family (germanium, silicon, etc.) and can generally be taken as relays.
There are two groups of transistors, as follows:
Type PNP:
For these transistors to allow current to pass:
The flow of the control current should be from the emitter towards the base
The flow of the current should be from the emitter towards the collector.
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