Lost with 50w LEDs + PWM

Hinjeniero:
Hope that running the LEDs at <55% plus a bunch of these fans the temperature won't raise too much.

Anyway before installing them, I will run some tests to see what could I expect in every single situation so I'll be sure that I won't blow up something or set my house on fire.

You should also plan for the Arduino crashing and leaving all the LEDs at 100%, eg. Add a fuse that can't handle that much power.

Fuses are cheap and might save you from killing some expensive LEDs due to a software glitch.

PS: Be sure to test it to see if it blows!

fungus:
It should be that simple, yes...

The amperage of those LEDs isn't too bad (300mA), that should make the PWM switching easier on the PSU than low-voltage/high-current LEDs. If you want to be extra sure you could add some extra capacitors on the power lines near the LED. Get come big ceramics.

Fans will make a big difference, yes

(if the noise doesn't bother you...)

I was thinking to add the capacitors between the psu and the MOSFET, because if I put them between the MOSFET and the LED, the final wave would be shark type or even almost linear. But in the other hand I think that the wave doesn't matter as long as the average voltage is the same so probably would be better as near to the LED as possible.

rickso234:
At first glance that heatsink/fan looks small for 50W... think they're for 5-10W LEDs. THere are some nice big, round LED heatsinks on ebay that should work without a fan. Is there good airflow in those ceiling fixtures?

http://www.ebay.com/itm/20W-30W-High-Power-Led-Heatsink-Aluminium-Cooling-For-20-Watt-30-Watt-Led-Light-/190774600422?pt=LH_DefaultDomain_0&hash=item2c6b0d62e6

If you want 15 separate PWM channels then you'll need some sort of multiplexer since Arduino only has 6 PWM channels... or you can run all the reds together, greens together, and blues together so only need 3 PWM channels.

Does the suggestion for "NMOS transistors" really mean NMOS FETs (N-channel MOSFETS)? Look for devices with low drain-to-source resistance (Rds) otherwise you'll waste power in the FETs and may need to heatsink them too. If driving the gate with a transistor (recommended since they'll drive the MOSFET gates with sharper-edged signals that minimize heating) you won't need "logic compatible" devices.

The problem with the heatsink is that I don't have too much space for it. The spot light has 50mm diameter so would be impossible to fit a 10cm diameter heatsink but there is enough space above the light to provide good ventilation.

I will use an arduino mega which has 15PWM so I could avoid multiplexing.

Since I don't know yet if the LED is common anode or common cathode there is not much I can do to find the transistor that I need but of course it has to be high efficiency because otherwise it will waste a lot of power. The lights will be on at least 7 hours every day so I need the system to be as efficient as possible.

fungus:
You should also plan for the Arduino crashing and leaving all the LEDs at 100%, eg. Add a fuse that can't handle that much power.

Fuses are cheap and might save you from killing some expensive LEDs due to a software glitch.

PS: Be sure to test it to see if it blows!

That's a very good idea, I was thinking how was the best way to reduce the maximum that the psu can supply in case of system failure and a fuse is just perfect.

The seller has answered, seems to be an expert about his products.

hi?dear,
but?i?don't?understand?your?question.
sorry
?
?
2013-01-22
xiangpailighting
?
?????eBay Member: rexaviis
??????2013-01-21?23:33
?????xiangpailighting
???????????: rexaviis ? 10W 30W 50W watt RGB Changing LED Bright Lamp High Power Chip For flood light????230827659562 ???????
xiangpai-lighting????

Hi, is it common anode or common cathode?

Thanks!

- rexaviis

I made a quick schematic (considering that is common anode) to have a visual reference, this is just for one the LEDs.

Is there anything wrong? Notice the resistor after PWM2, the red LED should work at less voltage than the other two so the resistor drops the input voltage in the third transistor. I prefer do this by hardware instead of setting a different PWM for the red LEDs by software, but I don't know if is the best idea.

PD: The voltages in the schematic are random, I don't know them yet.

PD2: I'm thinking to use this MOSFET (15 in total).

Manufacturer: IR
Manufacturer Part No: IRFZ44N
Package / Case: TO-220
RoHS: Yes
Datasheet: Click Here

Specifications
Transistor Type: MOSFET
Transistor Polarity: N Channel
Drain Source Voltage, Vds: 55V
Continuous Drain Current, Id: 49A
On Resistance, Rds(on): 17.5mohm
Rds(on) Test Voltage, Vgs: 10V

That schematic won't work, there is nothing to pull down the mosfet gates, also the transistors reduce the mosfet gate drive.

If the LED is common anode then you can use N-channel mosfets connected in a similar way to PWM the LEDs, but connect the mosfet gates to the Arduino PWM outputs through 100 ohms resistors (no transistors). Use logic-level mosfets. Also connect a 10K resistor between each of the Arduino PWM outputs and ground.

Hinjeniero:
The seller has answered, seems to be an expert about his products.

Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.

fungus:

Hinjeniero:
The seller has answered, seems to be an expert about his products.

Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.

Unfortunately, it also affects the circuitry needed. Common anode LEDs needing more than 5V can be controlled form the Arduino just with a N-channel mosfet or NPN transistor. Common cathode LEDs needing more than 5V require a P-channel mosfet or PNP transistor plus a level shift circuit, unless your 36V power supply has a floating output.

dc42:
That schematic won't work, there is nothing to pull down the mosfet gates, also the transistors reduce the mosfet gate drive.

If the LED is common anode then you can use N-channel mosfets connected in a similar way to PWM the LEDs, but connect the mosfet gates to the Arduino PWM outputs through 100 ohms resistors (no transistors). Use logic-level mosfets. Also connect a 10K resistor between each of the Arduino PWM outputs and ground.

You're right, forgot about pull down the gates. I think I fixed it.

dc42:

fungus:

Hinjeniero:
The seller has answered, seems to be an expert about his products.

Doesn't really matter...

The day they arrive you can just connect a low voltage across them and find out which way lights them up. The only difference it will make is the type of transistor you need.

Unfortunately, it also affects the circuitry needed. Common anode LEDs needing more than 5V can be controlled form the Arduino just with a N-channel mosfet or NPN transistor. Common cathode LEDs needing more than 5V require a P-channel mosfet or PNP transistor plus a level shift circuit, unless your 36V power supply has a floating output.

I didn't know that the transistor type would change depending of if the led is common anode or cathode, I thought it would be as easy as the second schematic I made.

dc42:
Unfortunately, it also affects the circuitry needed.

Not really. He's already using a BJT to drive the MOSFET gate. He just has to pick NPN or PNP and connect accordingly. It's not a radical change in design.

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.

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.

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

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

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

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.

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.

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

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.

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

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...

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?

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.