How to determine if LED Drivers are correct for LEDs

I just received some 10W RGB SMD LEDs.

The seller's specs read:

Model: 10W
Color: RGB
DC Forward Voltage (VF): Red 6-8V, Greed 9-12V, Blue 9-12V
DC Forward current (IF): 300MA
Out put Lumens: Red 120-150LM, Green 200-300LM, Blue 70-100LM
Wave Length : Red 620-625nm , Green 515-520nm, Blue 455-460nm
Beam Angel: 140 degrees
Life span: >50,000 hours

I've never seen a 10W LED light up so I connected it to a 9V transistor battery. All works, especially red since I pushed it with 9V.

There are posts in this forum similar to mine, but they don't seem to address how to handle the difference in voltage between red and green/blue. Also, the DC forward current for my LED is 300mA and I am seeing others talking about needing 350mA.

I'm a software developer, not an electronics engineer. I don't want to burn these LEDs out and I also don't want to catch the house on fire! :stuck_out_tongue:

My application is for various outdoor lights needing replaced. Each will be connected via NodeMCU Dev Board to control red, green and blue brightness. Each light is controlled using MQTT. A RaspBerry Pi is the broker.

Can anyone point me to a layman's How-to on determining hardware that will push this LED to its max rating correctly?

In other words, can a single 10W LED Driver be used for one of these LEDs even though forward voltage requirements are different? There must be a resistor or something needed to accomplish this.

Also, how do I limit forward current for each (red, green, blue) to 300mA?

A 10W driver that seems like it might work: http://www.ebay.com/itm/301815614382

Or should I use 3 of these: http://www.ebay.com/itm/231411107048

Does anyone know of a link/video that would help me understand what is needed here?

I've never seen a 10W LED light up so I connected it to a 9V transistor battery. All works, especially red since I pushed it with 9V.

Not really a good idea... The internal resistance of the battery may have saved you from frying your LED. If you would have measured the voltage you would have found it's not 9V with the LED connected.

In other words, can a single 10W LED Driver be used for one of these LEDs even though forward voltage requirements are different?

No. You can run multiple LEDs in series, but since RGB LEDs have a common connection (only 4 wires) you can't connect the internal LEDs in series.

Also, how do I limit forward current for each (red, green, blue) to 300mA?

With a special "constant current" power supply (or driver circuit). This type of power supply/driver provides the rated current and due to the characteristics of the LED, the voltage falls into place.

A 10W driver that seems like it might work: http://www.ebay.com/itm/301815614382

No.

Or should I use 3 of these: http://www.ebay.com/itm/231411107048

Yes, but I usually don't but the cheapest thing I can find on eBay :wink: .

You have two options.

Use a 12V supply and individual power resistors to limit current for each colour - advantage
1 supply, disadvantage lots of power wasted.

Use 3 300mA supplies (constant current), one for each colour.

The last link you gave are to avoided, they are extremely dodgy and I would never
attach those to the mains, you are risking life and property using non-certified supplies
and those are obviously not properly isolated to proper safety standards.

First of all, you're lucky 9V batteries are crap. Otherwise you would have certainly blown the red led :wink: Never voltage drive a led :wink:

The whole idea of the driver is to limit the current. So just get a 300mA driver for each (each color is 3W :wink: ) that can output at least 12V (max of the max led you want to drive) and you're done. They drive current, so you don't have to worry about the voltage part. You can get 3 types of drivers, step down type (supply with more then the 12V). step up (drive with less then the 12V) or step up down (they don't care).

Another thing to pay attention, does the LED have a common lead (common anode or cathode) the driver needs to have the current sensing in the not common lead.

It's also possible to use a common step up or down converter but then you have to modify it an most have the sens in the negative, so only work for separate leads or common anode. And most have a 1,25V orzo drop which is a bit high @ 300mA.

And it's better to slightly underdrive then then to overdrive them :wink: They will last wayy longer. You also need a pretty beefy heatsink to keep it cool.

MarkT:
You have two options.

Option 3, don't use mains drivers... Then you just get 3 drivers and 1 supply :slight_smile: Most of them are easier to dim/control from a uC

Need a part like this to control the current and not burn out anything
http://www.digikey.com/product-detail/en/microchip-technology/MCP1664T-E%2FOT/MCP1664T-E%2FOTCT-ND/5323386
Lots of other options
[http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-led-drivers/2556628?k=led%20driver](http://“http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-led-drivers/2556628?k=led driver”)

The RGB LEDs I purchased can be seen in the bottom of the image here:

http://www.ebay.com/itm/141822473474

septillion, you can see that the positive terminal is intact, but the seller or supplier has precut the negative terminal. Wish they wouldn't have done that... it could have been left longer, but I can deal with it. Does this answer your question regarding the common lead(s)?

To those of you who pointed out the dodgy drivers, thank you. I will avoid them for sure.

To further clarify the intended use and operation of these LEDs, as an example, I have a front yard light that sits on a brass pole about 5'-6' off the ground. It has 3-25 watt bulbs in it currently and is connected to 120v AC with a crappy photoelectric cell. I'm not sure if a single 10W RGB LED will match the brightness of 3-25 watt bulbs. It almost looks like it would be similar brightness if the 9V battery was any indication. (Btw, I thought I might blow the red leds and glad I didn't. Thanks to everyone for the warning on the 9V battery.)

So, I would like to be able to control the hue and brightness of these LEDs no matter how many I put in place using an ESP8266 WiFi and MQTT (not really relevant to my post). I understand I will need a good heat sink and probably a cooling fan. I think I'm hearing that brightness of each color (red, green, blue) needs to be controlled by using the voltage range specified. For red this would mean 6V is somewhere near the lowest and 8V is somewhere near the highest. This is 2 volts range from low to high, whereas the green/blue has a range of 9V-12V, or a 3 volt range.

The desired end result is to have a full range of colors and a full range of brightness.

I understand septillion's recommendation of 3 individual drivers, 3W - 300mA and 12V. This is a good start, though I'm still not understanding how the voltage is controlled remotely for each color. I have some 5050 RGB SMDs connected directly to GPIO port of a NodeMCU Dev Board using PMW, but I don't think I dare connect these 10W LEDs directly like that. What am I missing? :S

rwkiii:
I understand septillion’s recommendation of 3 individual drivers, 3W - 300mA and 12V. This is a good start, though I’m still not understanding how the voltage is controlled remotely for each color. I have some 5050 RGB SMDs connected directly to GPIO port of a NodeMCU Dev Board using PMW, but I don’t think I dare connect these 10W LEDs directly like that. What am I missing? :S

You turn them on and off using transistors to switch the power to the driver (MOSFETs are recommended for this). You always need to use an external transistor to drive something with the Arduino if it draws more than 20mA. You cannot do PWM unless you use a PWM capable driver.

You can also use a linear driver IC like the AMC7140, which uses a resistor to set the current, and has a pin you can PWM. These are less efficient (they dissipate the extra power as heat), but they’re easy to use an easy to PWM. This is usually my go-to for <700 mA LED drivers (what I do for bigger ones, people here would beat me up over, so I won’t talk about it)

A much worse way is to do it with a large (physically, as in, high power rated - 5W I’d say, minimum - those big white ceramic ones) resistor, like you would an indicator LED, only larger. This provides lousy control over the current, since the forward voltage drop on the LEDs falls as they get hot, so they will end up getting more current. But if you don’t push their specs, and put proper heatsinking on them, this is at least viable.

I'm understanding better. Found a link to a Youtube video that shows something like you were talking of for PWM. It looks interesting, but I don't see breakout boards like this anywhere.