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Author Topic: So called LED lighting drivers  (Read 1460 times)
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Hi folks, another newbie question. Not sure if this is the right forum as it seems more specialized with display LEDs, but I figured this might be the best forum to post this.

So I'm looking into controling several LED lighting circuits (abour 3-5W per circuit @12VDC). I've been looking at a lot of existing products out there, and most of them require LED "drivers" to drive them. So my question is: are the so-called LED drivers just bonefied AC-DC power supplies, or is there something special about these drivers?

And if I wanted to build a circuit to control (i.e. switch on and off) these LEDs circuits via the Arduino without using relays, any suggestion as to what type of circuit I should use? Assuming my power supply has enough juice, would a simple Dralington transistor suffice?

Finally, if I wanted to get fancy and try to dim these LEDs, would PWM work for dimming LEDs?

An advice will be appreciated!

Thanks,
- K.
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3-5W is a lot of current: 2.4A with 5W, 12V. You'd want something MOSFET based with real low Rds so they don't burn up. And to ensure they change states fast from low Rds (full on) to the off state, you need a MOSFET driver. That combination is what makes the LED driver.

PWM would work.
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are the so-called LED drivers just bonefied AC-DC power supplies,
It depends on what you are driving. Driving high powered LEDs require a constant current source where as driving lots of low power LEDs together so you require a large current just requires a normal power supply.
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Thanks everyone for your explanations! In that case, does anyone know of ICs that have multiple FET driver circuits (with low enough Rds) in a single package?

Thanks again!
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LED drivers are designed to drive LED loads typically in a constant-current (CC) mode.
Some drivers are constant-voltage (CV) and require a current regulator others are
CV/CC and can be operated either mode. The outputs are short-circuit (SC) and
open-circuit (OC) protected.

If you are looking at LED drivers with an AC input these will typically have power-factor (PF)
correction. Since there are a lot of outdoor LED applications a number of
drivers will have outdoor ratings for moisture as well as surge protection.

(* jcl *)

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Your question is too common, can you provide a link to datasheet/specification of your:
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LED lighting circuits (abour 3-5W per circuit @12VDC)
?
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Finally, if I wanted to get fancy and try to dim these LEDs, would PWM work for dimming LEDs?

An advice will be appreciated!

Thanks,
- K.

I'm really new to Arduino and planning to use it for RGB-light control. I have RGB-power leds + LED-drivers. LED-drivers from Dealextreme are quite cheap and comes with a PWM-dimmer.

http://www.dealextreme.com/p/mr16-3-1w-300-350ma-constant-current-regulated-led-driver-12-16v-input-13555
and
http://www.dealextreme.com/p/10w-500-lumen-multi-color-rgb-led-emitter-metal-plate-140-degree-44043

I'm planning to use 3x of those for each color (RGB) and use Arduino to control drivers via PWM.

The driver is PT4115E with almost identical to that reference board.
Here's a link to datasheet: http://www.micro-bridge.com/data/CRpowtech/PT4115E.pdf


ELECTRICAL CHARACTERISTICS
The following specifications apply for VIN=12V, TA=25 oC, unless specified otherwise.

VIN Input Voltage 6-30 V
FSW Max. Switching Frequency 1 MHz

DIM Input
VDIM Internal supply voltage DIM floating 5 V
VDIM_H DIM input voltage High 2.5 V
VDIM_L DIM input voltage Low 0.3 V
VDIM_DC DC brightness control 0.5-2.5 V
fDIM Max. DIM Frequency fOSC=500kHz 50 kHz
Brightness control range 5000:1

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I'm planning to use 3x of those [drivers] for each color (RGB) and use Arduino to control drivers via PWM.

You'll only need one of those drivers per color.  3*1W as in 3 x 1W = 3W.

Keep in mind that VDIM_H is 2.5V and the Arduino's PWM is 5V.  I've used the Arduino to control a PT4115 by using a voltage divider between the Arduino's PWM outputs and the 4115's DIM input.
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I'm planning to use 3x of those [drivers] for each color (RGB) and use Arduino to control drivers via PWM.

You'll only need one of those drivers per color.  3*1W as in 3 x 1W = 3W.

Keep in mind that VDIM_H is 2.5V and the Arduino's PWM is 5V.  I've used the Arduino to control a PT4115 by using a voltage divider between the Arduino's PWM outputs and the 4115's DIM input.

Sorry, I explained it wrong. You're right. 3 drivers per 1 RGB-led - one driver per color.

I've looked PT4115 datasheet, and VDIM max voltage is ~6V. So voltage divider isn't necessary IMO.
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Hmm, I remembered seeing 0.3-2.5V on the data sheet but I guess this is just for the analog dimming.  I guess it wouldn't really make sense to have a 0.3V PWM signal.  I guess I used up a bunch of resistors for nothing  smiley-lol
Carry on, let us know how it goes!
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