See also:
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Resistors
Buying a simple resistor can be a complicated
task. Here are some of the parameters
you
will need to decide on:
- resistance - measured in ohms, typically
from 1 to several million (a.k.a.,
"megaohm"),
the resistance measures the
amount of current
the device will allow to pass
it in normal
operation. The resistance of
most resistors
are marked with color bands
on the body for
easier identification.
- power rating or wattage - this describes
the heat tolerance of the device and typically
range from a quarter of a watt up to several
watts. Since higher resistance components
allow less current to pass through, they
typically are lower wattage devices. For
example, in a five volt DC circuit, a 10
ohm resistor would need to handle 0.5 amps
and 2.5 watts, whereas a 100 ohm resistor
in the same circuit would only need to handle
0.05 amps and 0.25 watts.
- tolerance - common carbon resistors are designed
to be within 5-20% of their
rating; more
expensive devices are designed
to tolerances
of 1% or less. If the actual
resistance is
important in your circuit,
you will need
to order one of the more expensive,
more
precise resistors. "Banded"
resistors
commonly show their tolerance
with a color
band.
- composition - in addition to carbon resistors,
other choices include carbon and metal film,
cermet film, wirewound, and metal glaze.
- packaging - the most common shape for a resistor
is axial, which means that the two leads
protrude from the center of the body of the
resistor as if they were a single wire running
straight through it. Resistors are also available
in surface mount and inline and dual inline
arrays.
Resistors are typically sold in packages
of 5 to 10, but some companies will sell
them individually. |
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