Pages: [1]   Go Down
Author Topic: Current liming arduino led driver from high current dc source  (Read 1082 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 30
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm interested in building one of the countless arduino led drivers that offer dimmability to the leds, but all the examples i have seen use mosfets and the like to pwm from an arduino signal. This works fine if you have a dc source of the correct amperage that is NOT a led driver. Since a led driver will want to push out a constant current, and the pwm will push back, or cause some issues with capacitor charging/discharging when switched on/off so much if they are wired after the pwm output. All i know is its unfeasable.

So my issue is that i want to drive ~10-100w of leds, 5w smd's, 10w smds, and a 40' ~75w rgb strip, and dim pwm them with the arduino. My dc supply will kick out ~10A 12v, its a voltage regulated output from a solar charger controller. Actually a picoups device meant for car computers, but thats charged by a seperate pwm charger w/ a 20w solar panel and a few sepics to help get more usable current, since below 13v it won't charge the battery. I figure get more watts in shady/clouds/dawn/dusk by just kicking up the voltage with a few sepics in parallel, and get a usable voltage at albeit lower current.

Anyway, not to get too far off topic, my question is how would you limit the current going into the mosfets pwm switching the led's to dim, but not supply a CONSTANT current as a typical led driver would? I've been advised thats a bad idea, as it would cause stress on the driver wanting to push 10x more power into the leds, but the pwm is pushing back by pulsing the output.

So, how would i go about finding what i need to supply the mosfets that power the leds at a certain amperage at 12v, that doesn't waste energy as heat through resistors, and the like. A efficient current limiter, and not constant voltage, that can handle a high input current like 12v dc 10a, and give me the max power needed for the led's with the least amount of energy waste as heat (ideally 50w max, i won't be running them full power/all of them as its for backup lighting in power failure situations, at least until i get a grasp on how to power them, then i wan't to get more panels and have all the lights solar powered).


For the TLDR, how do i limit the current from a 12v 10a dc source, to potentially down to a few watts/low amperage (no pwm) at max effeciency? Sepics perhaps?

I have 8 of these lying around to play with-

http://www.ebay.com/itm/140875280472?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Would i fry them if i hooked them up to a 12v 10a dc input? Or are they not like drivers, in that they can sip off a relatively low amount of current from a high current input. Also, could you then use these in parallel to power the mosfets at the correct maximum wattage for the led's to drive? Would they waste power or be stressed as a led driver/resistor would be configured as such?

Any advice is most welcome, i'm looking foreward to starting on my first arduino project, and would like any advice that can be offered as to doing this right/not frying hardware.

 smiley-mr-green

Thanks-

I know there are some sepic IC's that can do current limiting, but can't really find an answer to this problem.
Logged

United Kingdom
Offline Offline
Tesla Member
***
Karma: 224
Posts: 6614
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Your best bet is to buy dimmable switch-mode constant current drivers. Something like these http://www.led-supplies.com/led-drivers-LED-power-supplies/1-10V-PWM-Dimmable-Constant-Current-LED-Drivers.html. Or make your own if you are brave enough, there are plenty of ICs designed for power LED control.
Logged

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.

Norfolk UK
Offline Offline
Faraday Member
**
Karma: 69
Posts: 2552
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I built this http://arduino.cc/forum/index.php/topic,123665.0.html into 3 channel constant current circuit to drive a 10W RGB LED in a simple mood lamp.

* ATtiny-RGB Moodlamp.pdf (8.88 KB - downloaded 57 times.)
Logged


Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You can simply get one of those dc-dc converters with a shutdown pin for this. Those dc-dc converters will regulate the current going through the leds, and the shutdown pin allows you to pwm the current.
Logged

Pages: [1]   Go Up
Jump to: