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

Hinjeniero

Hi guys, first of all sorry for my bad english. I'm also a noob so this makes an awesome mix.

I'm a bit lost in my project and I need some guidance.

I'm trying to control 5 x 50w RGB led.



I couldn't find the datasheet and the only info that I have is this.

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

What I want to do is to control each single channel (RGB) of each led (5x3= 15 in total).

I'm gonna use exactly this psu.



http://www.ebay.com/itm/110933317767

Input Voltage Range  90~132V AC/ 180~260V AC by switch; 254-370VDC
Out    32-36V,0-9.7A

I know that I will have to reduce the output voltage more or less for each channel, that's not a problem, the problem that I have is this one.

Will I be able to use PWM through a transistor (one per channel) to control the intensity of each channel? Will I blow up something?

Thanks for the help!
no pain, no gain!!

macegr

Use some nice big NMOS transistors, and the slowest PWM you can bear. Might need to drive the gates higher than 5V to avoid heating.
Unique RGB LED Modules and Arduino shields: http://www.macetech.com/store

dc42

As those LEDs have only 4 connections, they are either common anode or common cathode. You need to determine which. The connection on the left is probably the common one. To determine the polarity, connect your power supply between that connection and one of the others through a 10K series resistor and see if there is a faint glow from it. If necessary, do it is a dim light and reduce the resistor to 1K.

I suggest you drive them through a mosfet+BJT constant current circuit, because your power supply gives very little spare voltage so a series resistor won't give good current regulation. The details of the mosfet+BJT circuit depend on whether the led is common anode or common cathode.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Hinjeniero


Use some nice big NMOS transistors, and the slowest PWM you can bear. Might need to drive the gates higher than 5V to avoid heating.


I'll take it on consideration, thanks!


As those LEDs have only 4 connections, they are either common anode or common cathode. You need to determine which. The connection on the left is probably the common one. To determine the polarity, connect your power supply between that connection and one of the others through a 10K series resistor and see if there is a faint glow from it. If necessary, do it is a dim light and reduce the resistor to 1K.

I suggest you drive them through a mosfet+BJT constant current circuit, because your power supply gives very little spare voltage so a series resistor won't give good current regulation. The details of the mosfet+BJT circuit depend on whether the led is common anode or common cathode.


I completely forgot to check if they are common anode or common cathode (I said I was a noob).

I don't have the LEDs yet, I just wanted to get ready before them arrive.

After a long time of searching I'm still unable to find the datasheet. I finally got to the manufacturer's website but there is not anything similiar to a RGB led so I give up. I'm just ask to the seller, I know it's a long shot but, why not to try it?.

Meanwhile I'm ordering the psu and  I'll test the LED when I got it. I just wanted to know if what I want to do can be done by the way I was thinking of.

I'll post the results as soon as I got it.

Thanks!
no pain, no gain!!

Headroom

#4
Jan 19, 2013, 10:54 pm Last Edit: Jan 19, 2013, 11:01 pm by Headroom Reason: 1
In general the inability to find  a data sheet would personally concern me, but I suppose that is normal for a lot of eBay stuff from ominous sources. Based on a recent post using that same sort of LED for Aquarium lighting, you should be able to find at least a data sheet for the single LED elements that they have assembled in this package.

Also make sure you have sufficient heat sinking, possibly using a fan if you intend to run these close to their max current. The 50000 h lifespan is likely not applicable if you run them at max current and will be definitely many magnitudes smaller if you don't heat sink properly.

A second suggestion is to use a switched constant-current power supply. Most high brightness LED drivers are switched constant-current power supplies for reasons of energy efficiency. Otherwise they would dissipate too much heat and also would need a lot of heat sinking. Energy efficiency is also the reason of a relatively low PWM frequency.

Perhaps if you post a little more about your project you'd also be rewarded with more pointed advice.

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