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The LED Dude
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5,876 Posts
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A 355nation Tutorial presented by
captainrab, brewer15650

Tutorial Name
LED Primer


Eye Protection
LED's are very bright. DO NOT look directly into the LED light!! The light can be intense enough to injure human eyes.




Basics on LED’s
How does a LED work? This is a very simple explanation of the construction and function of LED’s. Let's take white LED's for an example. They need 3.5VDC and use approximately 30 milliamps of current, a power dissipation of 100 milliwatts. The positive power is applied to one side of the LED semiconductor through a lead (1 anode) and a whisker (4). The other side of the semiconductor is attached to the top of the anvil (7) that is the negative power lead (2 cathode). It is the chemical makeup of the LED semiconductor (6) that determines the color of the light the LED produces. The epoxy resin enclosure (3 and 5) has three functions. It is designed to allow the most light to escape from the semiconductor, it focuses the light (view angle), and it protects the LED semiconductor from the elements.

As you can see, the entire unit is totally embedded in epoxy. This is what makes LED’s virtually indestructible. There are no loose or moving parts within the solid epoxy enclosure.

Therefore, a light-emitting diode (LED) is essentially a PN junction semiconductor diode that emits light when current is applied. By definition, it is a solid-state device that controls current without heated filaments and is therefore very reliable. LED performance is based on a few primary characteristics:



Voltage/Design Current
LED’s are current-driven devices, not voltage driven. 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.

Having said that if you are going to wire a number of LED’s in series then a current limiting resistor is usually needed or should be considered. There are however a few cases where a resistor is not needed if you add enough LEDs. See next paragraph



LED's in series without Resistors
You can wire LEDs in series without the need for a current limiting resistor. For a 12 volt automotive application (which is actually calculated around 14.5 volts) The reason is that each diode creates a voltage drop so each diode does not see 14.5 volts but more like 3.5 volts.

For example: 4 blue LEDs is equal to 3.5 volts X4 = 14.0 volts as each LED creates a 3.5 volt drop in the chain.

• 4 in series (blue, green, white, UV-black-light, pink) (3.5 volts X4 = 14.0 volts)


• 6 in series (red, yellow, orange) (2.3 volts X 6 = 13.8 volts )




Led's in parallel
I like this option because it's really easy, one LED, one resistor and just tie it across the power supply. Stack as many as you want. Having said that, though each diode will need a current limiting resistor.





Sizing current resistor for using LED's in parallel.
• A single LED (blue, green, white, UV-black-light, pink) needs a 470 ohm limiting resistor


• A single LED (red, yellow, orange) needs a 560 ohm limiting resistor



See attached drawings below which reflect data and principles:







Here are two sites that will calculate the current limiting resistor value for you.
Led current limiting resistor links


LED Resistor Calculator
LED Calculator - Current limiting resistor calculator for LED arrays

Ok, Now that your familiar with Led's and how they work. You might want to check out these How To's and use them as a guide when your working on your own conversion.

 

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The LED Dude
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5,876 Posts
Discussion Starter #5
On 12 volt single led applications a current limiting resistor is required so as not to blow the diode open. There is not a how to on the doors because I didn't document the polarity of the voltage present on the sockets. Having said that they are really easy to do but it requires a little patience. For white LEDs you would need to series a current limiting resistor with a value of 470 ohms as the tutorial suggests. Solder to the pads on the board. If it doesnt light up swap polarities on the led and that's it. One tip is to sand the 3mm led flat then apply a slight coat of clear grease so a's to spread the light. Try to match the height of the original led a's close a's possible. On the driver doors a t4 premade led replacement will work without soldering anything. The remainder of the doors however will need the led resistor Assy soldered onto the boards.
 
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