Lost with 50w LEDs + PWM

Other Hardware LEDs and Multiplexing
21

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.

22

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.

23

dc42:
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

24

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

25

fungus:
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.

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

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.

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.

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.

$T2eC16V,!y8E9s2fjtNhBQ4PnwBU8g~~60_57[1].JPG

26

I don't know any other way to find the voltage safely without destroying the LEDs.

If you supply them with the correct (and less than maximum rated) current and enough voltage to turn them on then it doesn't matter what the exact voltage is... the LED will drop whatever voltage it does given the supplied current. Look into buying/making some constant-current drivers for the LEDs. That way you set the current (in your case <300ma) and the driver puts out that current... no load resistors, no guessing, and not much wasted power. Maxim makes some driver devices as does On-semi. A driver circuit will cost more but is simpler and more efficient.

This device is pretty neat but it's only for up to 25V...

This one might work to regulate current but you'd still need the MOSFETs though. I just discovered it and you'd have to do some reading about it.

27

Hinjeniero:
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 only way to avoid wasting power when driving large LEDs is to use a switched mode constant current regulator. You can build them yourself around a switching regulator IC, inductor and a few other components, but they can be tricky to design.

28

rickso234:

I don't know any other way to find the voltage safely without destroying the LEDs.

If you supply them with the correct (and less than maximum rated) current and enough voltage to turn them on then it doesn't matter what the exact voltage is... the LED will drop whatever voltage it does given the supplied current. Look into buying/making some constant-current drivers for the LEDs. That way you set the current (in your case <300ma) and the driver puts out that current... no load resistors, no guessing, and not much wasted power. Maxim makes some driver devices as does On-semi. A driver circuit will cost more but is simpler and more efficient.

This device is pretty neat but it's only for up to 25V...
http://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF

This one might work to regulate current but you'd still need the MOSFETs though. I just discovered it and you'd have to do some reading about it.
http://www.onsemi.com/pub_link/Collateral/NSI50350AS-D.PDF

I've been reading about CC and CV, and CC seems to be the best way to drive LEDs, but I would have to buy/build 15 of those and the circuit will become more complicated and less reliable and efficient. I don't think it's worth to control every spot light individually so I decided that I will join the Rs, the Gs and the Bs to finally get just 3 channels.

I would say that every single color of every LED will forward like 600mA, therefore if I join the colors of the leds, the total current would be 600mA * 5 = 3A per color.

dc42:
The only way to avoid wasting power when driving large LEDs is to use a switched mode constant current regulator. You can build them yourself around a switching regulator IC, inductor and a few other components, but they can be tricky to design.

I've been watching how to build one and you're right, is tricky (and much more for me).

I'm thinking to buy 3 of these, put a heatsinks, and adjust the output at 2 - 2.5A.

![](http://i.ebayimg.com/t/DC-Constant-Current-3A-Converter-I-5-30V-LED-Driver-Charger-/00/s/NTQ3WDUxNw==/$(KGrHqEOKj8E6Wnp-ebKBOnY(wWteg~~60_12.JPG)

http://www.ebay.com/itm/DC-Converter-Constant-Current-3A-Voltage-2-30V-LED-Driver-Battery-Charger-LM2596-/270955376640?pt=LH_DefaultDomain_0&hash=item3f1632f000

Feature:

-Fixed turn lamps current,that can show charging or not
-Reverse Protection,add input reverse connect protection diode on it
-Output the counter-current diode to stop battery power back
-Use the special benchmark of IC, and high precision sampling resistance,is more stable

Specifications:

-Module Properties: Non-isolated step-down / Buck charge module;constant voltage module(CC CV) charging module 
-Input Voltage:DC 7~35 V 
-Output Voltage:DC 1.25~30 V ( adjustable, continuous output )  
-Max output Current: 3A  (if output power more than 15w,you can plug heat sink)
-Constant Range:0-3A (adjustable)
-Turn lamps current:CC value*(0.1),CC value will change with Turn lamp current.
-The minimum voltage difference:  2V   
-Output Power:Natural cooling 15W,  25W with heat sink
-Convert Efficiency:  Max 90% (higher Output voltage, higher efficiency) 
-Output Ripple:  20M Bandwidth(Just reference )  input 12 V output 5 V 3 A 60 mV (MAX)
-Full Load temperature rise:45? 
-No-load Current:   Typical 10mA  
-Load Regulation:   ± 1% 
-Voltage Regulation rate:  ± 0.5% 
-Dynamic response speed:  5% 200uS 
-Potentiometer adjustment direction:  clockwise (increase), counterclockwise (decrease) ,Close to the input  potentiometer is voltage regulation(CV), close to the output potentiometer is current regulation(CC)
-Indicator light:RED(charging);GREEN(finish charging)
-Output Short-circuit Protection:  Yes, Constant current
-Input Reverse Protection:  YES
-Output prevent reflux: YES, output have internally series against a prevent the diodes.
-Operating temperature:  Industrial grade (-40 ? to +85 ?) (ambient temperature exceeds 40 degrees, lower power use, or to enhance heat dissipation) 
-Wiring way: welding, add pin can be weldinged directly in PCB
-Size: 49 x 23.4 x 11.4 mm ( L*W*H )not include potentiometer
29

Hinjeniero:
I'm thinking to buy 3 of these, put a heatsinks, and adjust the output at 2 - 2.5A.

I was thinking of suggesting those to you. Here are some warnings if you use them:

  1. The input capacitor is only rated at 35V and you indicated you needed about 36V. You should be OK if you swap out the input capacitor for a 50V one, since the chip it is based on (LM2596) is rated at 40V continuous (45V abs max).

  2. Don't try to PWM those by switching the supply. However, if they have left pin 5 of the IC floating, then you can apply a 5V inverted PWM signal directly to that. This will be easy to do if your LEDs are common cathode.

  3. You shouldn't need heatsinks, because they are rated for 3A and you are only drawing 350mA from them.

  4. There may be quite a lot of ripple in the output current, because they are designed for up to 3A and you will be using them for only about 1/10 of that current. You could reduce the ripply by changing the inductor on the board for one with a higher inductance but lower current rating.

30

dc42:
3. You shouldn't need heatsinks, because they are rated for 3A and you are only drawing 350mA from them.

He;s looking at putting the LED's in parallel and therefore drawing 2-2.5A

31

abrookfield:

dc42:
3. You shouldn't need heatsinks, because they are rated for 3A and you are only drawing 350mA from them.

He;s looking at putting the LED's in parallel and therefore drawing 2-2.5A

I missed that bit. But it's a bad idea to connect LEDs in parallel - especially high power ones - because they are won't share the current evenly. The hotter ones have a lower forward voltage at a given current than the cooler ones, which causes the hotter ones to take more current, which makes them hotter...

32

dc42:
I missed that bit. But it's a bad idea to connect LEDs in parallel - especially high power ones - because they are won't share the current evenly. The hotter ones have a lower forward voltage at a given current than the cooler ones, which causes the hotter ones to take more current, which makes them hotter...

You're right, what would you recommend then?

Is a good idea buying 15 of these?

700×700 45.9 KB

http://dx.com/p/mr16-1-3w-650-700ma-constant-current-regulated-led-driver-8-40v-input-13557

Based on the PT4115

http://www.micro-bridge.com/data/CRpowtech/PT4115E.pdf

FEATURES 
z Simple low parts count 
z Wide input voltage range: 6V to 30V 
z Up to 1.2A output current 
z Single pin on/off and brightness control using DC 
voltage or PWM 
z Up to 1MHz switching frequency 
z Typical 5% output current accuracy 
z Inherent open-circuit LED protection 
z High efficiency (up to 97%) 
z High-Side Current Sense 
z Hysteretic Control: No Compensatio 
z Adjustable Constant LED Current 
z ESOP8 package for large output power application

I would have to change the capacitor for one of 40-50v and a resistor to set the output at 550mA.
Also to step down the vin from 32v to 30v but won't be a problem using voltage regulator that can handle 10A.

The construction of the pcb looks really poor but it's also really cheap ($1,49 for more than 10).

PD: I may need some help to change the resistor to get an output of 550mA.

That's the formula in the datasheet: Iout = 100mv/Rs therefore Rs = 100mv/550

Then, to get 550mA output, Rs need to be 0,181ohm (or the closest value) . I tough there was something wrong with the units (because for me less than a ohm is weird) but the resistor that comes in the pcb is R160 (0.16ohm) so it make sense.

33

Looks like that little driver would work, and certainly cheap enough.

...and a resistor to set the output at 550mA.
DC Forward current (IF): 300MA

I'm missing why you want to drive the 300mA LED with 550mA.

34

rather than modifying the reference resistor, why not go with these ..? http://dx.com/p/mr16-1-1w-320-350ma-constant-current-regulated-led-driver-8-40v-input-13553

35

rickso234:
Looks like that little driver would work, and certainly cheap enough.

...and a resistor to set the output at 550mA.
DC Forward current (IF): 300MA

I'm missing why you want to drive the 300mA LED with 550mA.

abrookfield:
rather than modifying the reference resistor, why not go with these ..? http://dx.com/p/mr16-1-1w-320-350ma-constant-current-regulated-led-driver-8-40v-input-13553

Because I don't think that the forward current is 300mA, it's suppose to be a bit less than the double.

If you look at the picture, the 50w version es almost 2 of 30w in parallel.

30w > 10leds in serie (300mA)
50w > 16leds in 8s2p (? mA)

36

Hinjeniero:

abrookfield:
rather than modifying the reference resistor, why not go with these ..? http://dx.com/p/mr16-1-1w-320-350ma-constant-current-regulated-led-driver-8-40v-input-13553

Because I don't think that the forward current is 300mA, it's suppose to be a bit less than the double.

If you look at the picture, the 50w version es almost 2 of 30w in parallel.

30w > 10leds in serie (300mA)
50w > 16leds in 8s2p (? mA)

16 + 16 + 16 = 48

37

abrookfield:

Hinjeniero:

abrookfield:
rather than modifying the reference resistor, why not go with these ..? http://dx.com/p/mr16-1-1w-320-350ma-constant-current-regulated-led-driver-8-40v-input-13553

Because I don't think that the forward current is 300mA, it's suppose to be a bit less than the double.

If you look at the picture, the 50w version es almost 2 of 30w in parallel.

30w > 10leds in serie (300mA)
50w > 16leds in 8s2p (? mA)

16 + 16 + 16 = 48

That's the total number of leds in the matrix , but there is only 16 per color. Each CCsupply will drive a single color of each matrix (3channels per matrix = 15 CCsupply in total) and that's why I'm calculating the maximum current for every color and not for the whole matrix.

38

The current does not increase with the number of LEDs in series. That is why it is called a constant current power supply. What changes is the forward voltage so...

If you've got 10 LEDs in series with a 300mA current rating and 2.5 Vf/ LED then you still need to supply 300mA to the LEDs but 10 x 2.5 + X Volt for it to work.

39

I have a few 10watt of these models, same thing only smaller.

To compare, I used a cree ssc p7 (12watt) the ebay ones use double
the power and give off a lot less light than anything i've seen from
Cree or SSC and even NXP (Phillips)

Because of the high wattage, a switching regulator for power, then use
PWM through an n mosfet, tie the base to gnd with a 10k resistor
and you should be good to go.

with these 10watts i have i'm just going to use power transistors, via pwm
with a 200ohm resistor on base, roughly 20ma per pin vs next to no current
on a mosfet.

40

I can see the point about each color drawing 500ma...
16 LED per color so with 48W total (48 LEDs), power for each color is around 16W. Using P = I*E, or I = P/E, I = 16W/32v or 500mA.