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Topic: Lost with 50w LEDs + PWM (Read 9 times) previous topic - next topic

dc42

That first schematic is OK. If each mosfet is only switching one LED (max 330mA), then you don't even need to use mosfets, you can use NPN transistors such as BC337, with a 220 to 470 ohm resistor between the base of the transistor and the Arduino output, and no pulldown resistor.

The second schematic unfortunately won't work, because it will only pass a very low voltage to the LED. Unless the supply for the LEDs has a floating output, you need an NPN transistor followed by either a PNP transistor or a P-channel mosfet.
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Hinjeniero

Ok, I understand it now. I'm not sure about the specs that I got from the seller and I guess that each LED will take much more than (330mA). I'll run my own tests to be sure and then I will decide which transistor to use.

Thanks.

PD: I found this picture and I would say that is common anode because of the colors of the clamps but, of course, it's not sure.

no pain, no gain!!

fungus


That first schematic is OK.


The red LED needs about 10V less than the blue/green so it might need a resistor to absorb the extra volts.

10V@300mA = 33 Ohms, although it will need a large wattage.

Something like this should be enough: http://www.ebay.com/itm/271109598315
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rickso234

> The red LED needs about 10V less than the blue/green so it might need a resistor to absorb the extra volts.

Each LED needs a resistor to limit current, but yes, the red LED needs a different value from the rest.

As for taller heatsinks, look at these...

http://www.ebay.com/itm/Heat-Sink-for-20W-30W-50W-LED-/380534842067?pt=LH_DefaultDomain_2&hash=item5899a4e2d3

http://www.ebay.com/itm/20W-30W-Led-Light-Heatsink-With-FAN-Aluminium-Cooling-For-20W-30W-Led-12V-/190785568355?pt=LH_DefaultDomain_0&hash=item2c6bb4be63

Hinjeniero

#24
Jan 22, 2013, 01:15 pm Last Edit: Jan 22, 2013, 01:17 pm by Hinjeniero Reason: 1


The red LED needs about 10V less than the blue/green so it might need a resistor to absorb the extra volts.

10V@300mA = 33 Ohms, although it will need a large wattage.

Something like this should be enough: http://www.ebay.com/itm/271109598315



I'm trying to avoid the use of resistors to limit the current directly to the led because it's a waste of power. I prefer (if possible) to limit the current trough the MOSFET.


> The red LED needs about 10V less than the blue/green so it might need a resistor to absorb the extra volts.

Each LED needs a resistor to limit current, but yes, the red LED needs a different value from the rest.

As for taller heatsinks, look at these...

http://www.ebay.com/itm/Heat-Sink-for-20W-30W-50W-LED-/380534842067?pt=LH_DefaultDomain_2&hash=item5899a4e2d3

http://www.ebay.com/itm/20W-30W-Led-Light-Heatsink-With-FAN-Aluminium-Cooling-For-20W-30W-Led-12V-/190785568355?pt=LH_DefaultDomain_0&hash=item2c6bb4be63


The first one is perfect, tall but the base is small, it would fit. The second one there is no way I could fit it in the spot light.

Speaking about the voltage of the LEDs, I found something interesting.


Code: [Select]
30W:
Color: RGB
DC Forward Voltage (VF):  Red 22-24V, Green 32-34V, Blue 32-34V
DC Forward current (IF): 300MA
Out put Lumens: Red 400-500LM, Green 600-800LM, Blue 200-300LM
Wave Length : Red 620-625nm , Green 515-520nm, Blue 455-460nm
Beam Angel: 140 degrees
Life span: >50,000 hours


50W:
Color: RGB
DC Forward Voltage (VF):  Red 22-24V, Greed 32-34V, Blue32-34V
DC Forward current (IF): 300MA
Out put Lumens: Red 400-500LM, Green 600-800LM, Blue 200-300LM
Wave Length : Red 620-625nm , Green 515-520nm, Blue 455-460nm
Beam Angel: 160 degrees
Life span: >50,000 hours


The specs for 50w and 30w are the same but the layout of the array of LEDs is completly diferent!! (see the attachment)

In the 30w version , for every color, there is 1 row of 10 leds and in the 50w version you will see 2 rows of 8 led.

Since the 10w version is 3 led per row and the 20w is exactly doble and the voltages match, it easy to figure out the voltage for the 50w version.


Code: [Select]
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


20W:
Color: RGB
DC Forward Voltage (VF):  Red 13-15V, Greed 18-20V, Blue 18-20V
DC Forward current (IF): 600MA
Out put Lumens: Red 260-300LM, Green 400-600LM, Blue 150-200LM
Wave Length : Red 620-625nm , Green 515-520nm, Blue 455-460nm
Beam Angel: 140 degrees
Life span: >50,000 hours


If the 10w red is 6-8v and contains 3 LEDs then 7/3= 2.4v per LED. Therefore the 50w version,wich contains 8 led (in each row) will be 19.2v.

Applying the same for the other 2 colors we will have than the green and blue are 28v each.

I don't know any other way to find the voltage safely without destroying the LEDs.
no pain, no gain!!

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