Surface mount LEDs

Surface mount devices (SMD) are more common than ever thanks to miniaturization. LEDs inside disk drives, modems, and small personal electronic devices are more often SMD devices these days. ...
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The myth of the 5 volt LED

A commonly encountered question on message boards and in my email inbox deals with the elusive “5V LED,” and goes something like this: I have a 5V blue LED, can ...
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Why do I need a resistor with an LED?

Why do you need a resistor with an LED? The short answer: to limit the current in the LED to a safe value. The long answer: LEDs are semiconductors, diodes in ...
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How many LEDs can I drive in series?

It depends on your supply voltage. You have to be able to overcome the cumulative forward voltage of the series combination in order to get them lit. As an example, ...
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How do I drive LEDs from alternating current?

Without getting into a detailed circuit design, there are a couple things to think about when using an AC source. Diodes will conduct only when forward biased, so with AC ...
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How do I replace an LED with a brighter LED?

Generally, improvements in brightness have come about a result in improvements in manufacturing processes and materials. The electrical characteristics of the brighter LEDs don’t differ drastically from the older generation ...
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How are infrared LEDs different?

There are a couple key differences in the electrical characteristics of infrared LEDs versus visible light LEDs. Infrared LEDs have a lower forward voltage, and a higher rated current compared ...
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What is thermal runaway?

When a junction gets warmer, the current through it at a given voltage will increase. The increased current in turn heats the junction further, and the problem gets worse. Eventually, ...
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What kind of resistor should I use with an LED?

The important considerations when you’re selecting a current-limiting resistor are the value in Ohms and the power rating in Watts. The LED resistor calculator can help you determine both values ...
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What is the useful life of LEDs?

When you buy a package of light bulbs, you’ll see a number on the box that says something like “Life: 1125 hours.” This is defined as the time it takes ...
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How do I convert between candelas and lumens?

You can’t directly convert since they measure different things. The most useful explanation I’ve found is that lumens measure light output at the source, while candelas measure the light emitted ...
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Are LEDs inherently directional?

No. One way for a manufacturer to boost the luminous intensity spec (usually given in candelas or millicandelas) is to focus the beam more tightly. The same light flux, focused ...
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