LED driver

Thread Starter

cminke

Joined Jun 7, 2014
64
So after some revisions and updates im having to change my plans again and I'm looking for the best way to power 6 RGBW LED. with (If max) of 4A (3A red so I'm aiming for 3A around) and an (Vf) of ~3.2v (red is about ~2.8v) and assume its being powered by a car.

Last thing, I also have MINIMAL space!

4ch
6x 4ch leds @3A/each ~2.8-3.2v
PWM dimming

I was wondering if I could have one power rail and use NexFETs to switch the ground on the leds with a resistor on the red to drop that .4v

The board will have SMT leds and SMT parts with taller TFT reverse mounted / SMT on rear
 

Thread Starter

cminke

Joined Jun 7, 2014
64
anyone? it seems to be a challenge to find a 3A driver that also is a step up to ~21v, a driver that is a boost buck or SEPIC to ~10.5V@6A, or a 3.5V to 21A driver
 

wayneh

Joined Sep 9, 2010
17,153
So help me understand your goal. You want to control 6 multi-color (4 channel) LEDs. Do you want them to be fully independent, or will they do the same thing all together? These are not smart LEDs, meaning you have to PWM the power to them to control them, versus controlling them by a small PWM signal. Right?
 

Thread Starter

cminke

Joined Jun 7, 2014
64
Yes, PWM for dimming each color individually but all 6 leds at the same time.

The end goal is to flash the leds in different: brightness, colour and sequences, for an experiment and research for public safety equipment.

BASICLY a lightbar for a emergency vehicle that will not be used on the road but rather as a research tool!

For all intents and purposes, assume I'm building a light bar, and I'm designing the internal module.

The LEDs I've picked are the brightest in their size class but use a lot of amperage, I'm going to be experimenting with different duty cycles and flash rates to keep thermals down.






the details of the leds are attached
 

Attachments

wayneh

Joined Sep 9, 2010
17,153
Yes, PWM for dimming each color individually but all 6 leds at the same time.
OK, well one simplification you can make is to arrange the 6 LEDs into two parallel strings of 3 each, 4 color channels for each string. You'll have enough voltage to beat the combined Vf and the total current will be much lower with just two strings.

I additionally believe you can then "waste" a bit of the power in a simple current-limiting resistor for each channel of each string. The efficiency loss really won't be too bad, and the gain in simplicity is great. With those 8 total resistors in place (two strings, 4 channels each), you could PWM each color channel, both parallel strings of that color, using a single MOSFET. Four MOSFETs total, one for each channel. The four PWM signals - the brightness of each color - could come from a micro such as Arduino, from one of the many PWM modules you can find on eBay, or whatever.

Making sense?
 
Last edited:

Thread Starter

cminke

Joined Jun 7, 2014
64
you sir, make a lot of sense! Except when you work out the numbers...... 3000mA with a VF or only 8.4v Max (red) 10.2Vmax (Blue/ white)

that's 10w on the red Ch, and 5.4w on the blue& white and then green in the middle, point is thats ALOT of head and space is limited. soooo thats going to be a no-go partner. but thanks for the input!
 
Last edited:
Top