Page 68 - Sensors and Control Systems in Manufacturing

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original intensity after 50,000 hours, it is at the end of its useful life,
although the LED will continue to operate as output diminishes.
®
Unlike standard incandescent bulbs, DDP LEDs resist shock and
vibration and can be cycled on and off without excessive degradation.
1.13.6 Voltage/Design Currents
LEDs are voltage-driven—in other words, they are current-driven
devices. Although drive current and light output are directly related,
exceeding the maximum current rating will produce excessive heat
within the LED chip due to excessive power dissipation. The result
will be reduced light output and reduced operating life.
LEDs that are designed to operate at a specific voltage contain a
built-in current-limiting resistor. Additional circuitry may include a
protection diode for AC operation or a full-bridge rectifier for bipolar
operation. The operating current for a particular voltage is designed
to maintain LED reliability over its operating life.

1.13.7 Heat Dissipation
When many LEDs are mounted into a small area, heat generation
must be taken into consideration. If there is a possibility that the
ambient temperature may exceed 60 degrees centigrade, some kind
of forced cooling system will be needed.
The ambient operating temperature must be taken into consider-
ation when a product/system is being designed. Certain limits exist
to maximum current at certain temperatures, which must be kept in
mind.

1.13.8 EMI Countermeasures
When instantaneous power failure or a current surge by lightning
stops the controller at abnormal conditions, the abnormally high elec-
tric current may continue running through the LEDs for an extended
period of time. This can damage the LEDs in the system. Circuit pro-
tection against abnormally high current must be built into the system
to protect against this.

1.14 Non-Phosphor White LEDs at a Viewing
Angle of 30°
A non-phosphor white LED is shown in Fig. 1.14.

Description:
• Superbright LED Lamp
• Round type