set entirely by the feedback network.
They are widely used when a closely controlled amount of gain
or some form of signal processing is necessary in an electronic
system.
The branch of electronics dealing with devices that
generate, transform, transmit, or sense optical, infrared, or
ultraviolet radiation, as cathode-ray tubes, electroluminescent
and liquid crystal displays, lasers and solar cells.
A light-emitting diode is a semiconductor diode that
converts electrical energy into light when an alternating current
is applied.
Note: This does not apply to flashing LEDs.
Flashing LEDs can be driven from a voltage source, i.e. without
a resistor
A liquid crystal display is a screen in which a liquid
crystal material
sandwiched between two sheets of glass exhibits computer
data when a voltage appears across leads that are connected
to character-forming segments etched onto its inner glass surface.
An optocoupler, also known as an optoisolator,
is a semiconductor device that allows signals to be transferred
between circuits or systems, while keeping those circuits or
systems electrically isolated from each other.
|
|
Fuses provide reliable and low cost protection
against excessive currents, which occur during overloads. There
are many different types and styles of fuses and selecting a
fuse for a particular application can be difficult.
When replacing a blown fuse, try to obtain
a fuse with a rating as close as possible to the original. If
it is not possible to locate an exact replacement, remem-ber
this a higher current fuse will offer less protection to the
equipment, increas-ing the risk of dam-age and fire. A lower
current fuse will offer more protection, but will be more prone
to nuisance blowing. Therefore, it is better to substitute a
lower value fuse until the correct type is obtained.
This indicates the current carrying capacity of a fuse
under a particular set of test conditions, at 25 o C. Fuses
operated at a higher temperature need to be de-rated and allowance
must be made for any surge that occurs during switch-on. It
is generally recommended that fuses be specified at 125% of
normal load current in order to avoid nuisance blowing.
This is the maximum circuit voltage at which a fuse
can be relied upon to safely interrupt an over-current. At voltages
higher than the rating, a fuse may not be able to suppress the
internal arcing that occurs after the fuse link melts. In electronic
circuits, where limiting impedances ensure that the fault current
is kept low so that a destructive arc cannot occur, fuses may
sometimes be used beyond their specified voltage rating.
Standard fast acting fuses are designed to open very
quickly during an overload. They are not designed to withstand
the inrush current or switch-on surge that occurs in some equipment.
Time delay or slow blow fuses are designed
to tolerate the temporary overloads that occur during switch-on,
but they still blow quickly if subjected to gross overloads
during faults. Slow blow fuses are commonly used in the primary
circuits of electronic equipment, where the initial surge can
be many times the normal load current. Slow blow fuses and fast
acting fuses are not interchangeable due to their different
time characteristics.
It should be understood that the overload needed to
cause even a fast acting fuse to open quickly must be of the
order of 200% or more. An overload of only 35% (ie. a 4A through
3A fuse) could take an hour to open a fuse. |
|
