LED and BuckBlock Configuration

I'm working on making a photo enlarger which requires turning on/off and dimming several LEDs. I've been trying to figure out how to drive them but am way lost!

I got 1W LEDs off ebay that claim a forward voltage of 3.2v - 3.4v and a forward current of 350mA.

Question 1:
I got a LuxDrive BuckBlock A009 1400 mA driver. In hindsight, this is the wrong driver... I can't wire 4 LEDs in parallel to get up to 1.4A, correct? I'll need a 350mA dimmable driver and put the LEDs in series, correct?

Question 2:
I'll probably want to drive 5-10 LEDs.. what metric do I need to look at on a driver to make sure it's adequate?

Question 3:
On a related note, I get how to dim the driver, but when turning the LEDs on and off, should I use the dim wires or just cut power to the driver?

Any general pointers or driver recommendations would be really helpful.

Thanks everyone!

I'll need a 350mA dimmable driver and put the LEDs in series, correct?

Correct.

what metric do I need to look at on a driver to make sure it's adequate?

Typically, constant-current power supplies are rated for current and maximum power (watts). But, you can check the maximum voltage too.

On a related note, I get how to dim the driver, but when turning the LEDs on and off, should I use the dim wires or just cut power to the driver?

The "industry standard" is 10V PWM for dimming. You'll need a 10V power supply and a transistor or MOSFET driver circuit to "boost" the Arduino's 5V PWM. Sometimes 10V is generated internally and there is an internal pull-up resistor so a pot can be used for dimming (0-10VDC). In that case you can just use a transistor or MOSFET.

Of course you can cut the power to turn it off, but for pulsing or dimming the constant-current supply will "try" to hold constant-current so that won't work well. (With a dimmable supply, it's technically "controlled current" rather than "constant current.)

Thanks for the reply, makes sense! Although I was looking at a data sheet and I think I might be able to drive the LEDs in parallel. I might give it a shot.. worst case I toast some LEDs but learn a valuable lesson =)

Hi,

You should be driving the LED in series, using a constant current supply that can vary the current from very low to 160ma. The driver must be able to output a voltage in the range of 12 to 15 Volts to power you 4 LEDs

I've been looking for the same type of item on eBay. The only options I have found is a linear supply based on an LM317. It will work but will tend to get hot and not be particularly efficient.

The A009 BuckBlock you purchased will vary the voltage until the current is 1400 ma. Nearly 10 times what your LED's are rated for. Will light them really bright then they will burn out.

If you connect the LEDs in parallel than each LED will get approximately 350ma in the best case and due to the variations in LED voltages the LEDs will likely get difference levels of current perhaps ranging from 100 ma to 500 ma each or perhaps more.

JohnRob:
I’ve been looking for the same type of item on eBay.

Low voltage PWM LED driver.
Sparkfun LED driver.
Sparkfun three-in-one.
leo…

If you connect the LEDs in parallel than each LED will get approximately 350ma in the best case and due to the variations in LED voltages the LEDs will likely get difference levels of current perhaps ranging from 100 ma to 500 ma each or perhaps more.

Ohhhhh, that’s the piece I was missing about why it’s better to run them in series. Thanks for that!

I ended up getting a boost puck . It’s a little spendy, but I’ll only need a couple of them and I’m fortunate enough to be at a point where I can throw a little money at problems to make them go away =)

For dimming I got a digital potentiometer. It’s a 10k chip, but I’ll just use half it’s range.