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How to Use a Solderless Breadboard
Written By: John R. Sewell

All LEDs, even High Lumen LEDs or also called Super Bright LEDS are Constant Current devices NOT Constant Voltage. Regardless of how they are listed, All LEDs require some form of Current Control and with the High Lumen LEDs you will need to control heat. Heat is the most 8mm Super Bright White, 100000mcd LED common failure cause with High Lumen LEDs. As the temperature rises the Forward Voltage decreases causing an increase in current; more current, more heat etc.; this is called thermal runaway and is destructive. If available a Constant Current supply designed for LEDs should be used. Theas supplies will be specified with a current output such as 1A, 900mA and show a compliance Voltage Range. Most power supplies are Constant Voltage output and require the use of a current limiting resistor.

Always be sure to understand the specs. Many sellers of LEDs say “9-12V” this doesn’t mean you can you can throw a 12V supply on it. The Voltage range listed is the Forward Drop of the LED. Since most High Lumen LEDs are not a single LED but constructed of multiple LED 12 Lumen Blue Super Bright LED Module, 12VDC “Chips” connected in series, parallel and combinations of both. An example is a 3W LED listed with 9-12V Forward Voltage. It will contain 3 chips all with a forward drop of 3-4V connected in series and requires a current limit of .3A(300mA). Since they are is series, all will use the same 300mA current. Higher wattage units can contain 100+ individual LED chips and will specify a Current and a Voltage. Example is a 10W unit with Spec listed as 9-12V Forward Voltage @ 900mA. This will contain 9 matched “chips” connected as 3 sets of 3 series LEDs in parallel. Doing the math; we get 3 LEDs in series at 3.4V with a 10.2V Vf with 3 times the series current of 300ma. = 900mA which yields us an approximate 10W LED. Other combinations give Forward Voltages of 18-24, 32-36 etc. A 100W Array will have 10 rows of 10 “Chips”, with a Forward Voltage of 32-36V (10x3.2-3.6V) and a current requirement of 3.5A (3500mA). Check the specification for a current limit value, usually listed as a test value or a max value. Operation under this Max value is the safe range.

Lets start with current; an LED that says that it is 10W, first, what does this mean? Power equals E X I or Power=volts time current so a 10W LED could be anything that gives us 10 as a product. Here the device physics jumps in; LEDs have a “forward drop”, White around 3-4V while Red around 1.8-2.5V per chip. If we just stuck 12V on the unit, it would almost immediately blow as the current was only limited by what the supply puts out. So we must add a series resistance to limit the current.

If we have a 10W White LED with 3”Chips” we now have a Vf Drop of approximately 10 volts, a specified current of 900mA, then we must use a resistor equal to:
1. 12V – forward drop or 12-10=2V
2. E/I=R 2/.9 = 2.2 ohm resistor
3. Resistor Wattage= I2 x R (IxIxR) or .81 x 2.2= 1.78W
So we would use a 2 to 5W 2.2ohm Resistor

The heatsink is required to remove as much heat as possible from all those “Chips”. Most High Lumen LEDs list 50degree “C” as a maximum temperature. Even this limit will cut the life from the typical 50 90 Lumen Super Bright Warm White SMD LED thousand hours. The Sink should be a large as physically possible while considering the environment to be used. Use in warm or hot areas, sealed enclosures or outside all may require larger heatsinks; where air conditioning, fans, drafts can use smaller heatsinks. Finned Sinks should allow linear flow along the fins. Vertical finned sinks to allow for drafting of rising of heated air so are more efficient than other styles. Dissipation to room air is encouraged. If the LED is a 30W then you must remove 30W of heat so a loose “Rule of thumb” is for use in a typical room temperature (25C) with free air flow environment, and vertical fin alignment; figure using a aluminum heatsink with a surface area of 6500mm2 per Watt (10 in2/W) so our 30Watt High Lumen LED needs a heatsink with a surface area exceeding 30 in2.

Heatsinks, the LED package, thermal pads, etc. all have thermal resistance. These all “add” together to give you a total degree rise/watt. The point here is not to beat to death math but to give you an idea into the use of High Lumen LEDs.
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