Specifications

33
The Recognised Name In Security
Cathode
Anode
__
+
1N4001
Current Flow
Cathode
__
Anode
+
Current Flow
Component
Diagram symbol
Diodes are necessary in the following applications:
* Connecting two sets of switches to the same trigger in
put, e.g. bonnet and boot.
* Flashing two separate parking light circuits with the same relay output.
* Sending two different circuits control pulses while keeping them isolated from each
other.
* Preventing feedback through the windings of relay coils.
N
ote: Diodes do cause a voltage drop across a circuit just as a resistor does, but it
is only about a 0.7 volt drop, so be aware of this when designing circuits using
diodes.
When installing diodes, they should always be selected with consideration given t
o
their maximum current handling capacity. For instance, if a diode is needed to
isolate one power source from another, it should be selected on the basis of the
maximum current that the circuit could possibly draw. If the circuit in question could
potenti
ally draw five amperes, then the correct diode should be rated for at least
five amperes. It is often better to use a diode of a greater current value than
needed just to be on the safe side.
RESISTORS
What is a resistor?
-
A resistor is a device used to
reduce the amount of current
flowing through an electrical circuit. They are generally manufactured from carbon
but higher wattage capability ones are usually made of wire wound around a
ceramic former.
The value of the resistor is usually printed on th
e wire wound type, and carbon
types use a colour band system to denote their value. The first band gives the first
number, the second band gives the second number. The third band is the number of
zero’s that must be added (the multiplier). The band on its
own is the tolerance
band; this indicates how accurate the resistance is, the most common are shown.