Page 71 - Testing Electronic Components
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Testing Light Emitting Diode (LED)
Typical LED
Light emitting diode (LED) is a diode that produces light when current
flows through it, when it is forward bias. The LED does not emit light
when it is revered-biased. The LED is used as a low current indicator
lamp in many types of consumer and industrial equipments, such as
monitors, TV, printers, hi-fi systems and machinery control panels.
The plastic lens is very important in directing and modifying the small
amount of light emitted by the LED chip. Light can be visible, such as
red, green, yellow and white. It is label as LED in circuit board.
An LED only needs about 2v across its anode and cathode terminals to
make it emit light. If a higher voltage is used, the current which flows
through it may be high enough to damage it. In order to limit current
when an LED is used at higher voltages, a resistor must be connected in
series with it.
The cathode of the LED is identified on the package by the flat side on
the plastic. The life expectancy of LED is about 100,000 hours.
flat anode
cathode anode
cathode
General appearance and Symbol for a light emitting diode.
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