BuckPuck question

(This kind of relates to my previous post 'Heatsinking a 3W Luxeon').

Anyone know anything about BuckPucks for Star LEDs? I've never used one before, and I'm confused about the voltage requirement. I am not using batteries.

I want to use a Luxeon 3W (is that the Luxeon III?) Star LED. I have a

1000mA BuckPuck that I also purchased which apparently accepts voltages between 5 and 32V. There's a couple of questions about the connectivity of these two devices that remain unanswered . yet I have been searching frantically on the web!

If I want to run a single 3W green Luxeon Star LED using the 1000mA rated BuckPuck, is the voltage applied to the BuckPuck important? Hypothetically speaking, say if I apply 12V to the BuckPuck, does the LED also get the 12V or does the BuckPuck reduce it down automatically to suit the LED's requirements without me doing anything? It doesn't say anywhere (that I can see) in the LuxDrive 3021 BuckPuck Product Manual that proper voltage input is important according to the LED configuration, and what you need to do.

I will not be supplying the full 1000mA to the LED - I will be reducing the power down a bit using the BuckPuck's optional pot. Hopefully this would allow me to reduce the power a little somewhere around 850-900mA.

Thanks

Jason.

Reply to
Jason S
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Oh, also, it says, "The on-board 5VDC output/reference provides power to external control circuits, eliminating the need for additonal power supplies mounted on the PC board".

Is this 5V output fixed current also? I want to be able to connect it to a couple of IC's on another board.

Thanks again Jason.

Reply to
Jason S

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Find your answers here:

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If you want to use the 5V output you should provide at least 5V25 at the input. The 5V output is not fixed current but it will have an upper limit.

--DF

Reply to
Deefoo

OK, let's assume I *do* connect say 5.25V so I get the 5V output (which is my second priority). According to the text found in the link you provided me : "Unlike standard power supplies, which deliver a fixed voltage to the output, the 3021 is designed to deliver a fixed current. The output voltage will vary as required to maintain the specified output current with differing forward drop voltages of LED junctions." ... Does that mean my 3W Luxeon would work just fine with that particular voltage? Even if I increased the voltage? Sorry, better to be safe than sorry - I find this a little confusing.

Jason.

Reply to
Jason S

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The typical forward voltage for the green Lumileds LXHL-LM3C is 3V7 @ 700mA (see Lumileds Technical Datasheet DS46) so if you hook up your BuckPuck to at least 5V25 and your LED to the BuckPuck then you should be allright for both the LED and the 5V output. When, in this setup, you actually measure the voltage over the LED you should see a value close to the mentioned forward voltage (if you use a current of 700mA of course).

--DF

Reply to
Deefoo

Thanks DF. I hooked up my green 3W Star LED for the first time (not for very long because my CPU heatsink didn't have its cooling fan connected yet), and wow it's bright... hurts my eyes when i look at it. Anyway I meausured the voltage across the LED like you said, and it was close to the 3V7.... 6 volts was applied to the BuckPuck initially. I reduced the current ('Set and Forget' Inbuilt Pot) of the BuckPuck down to around 800mA so it wasn't giving out the full 1000mA. The external 5K pot worked fine for dimming, woo hoo. Gradually I increased the voltage to the BuckPuck to 9V, then 12V (my main power supply is 12V you see). All seemed well - Voltage across the LED remained between 3V4 and 3V8 without dimming). Hope nothing goes wrong *fingers crossed*. I am relying on that BuckPuck!

Jason.

Reply to
Jason S

Hey Jason, LEDs in general are very temperamental about the power that is supplied to them. The BuckPuck as noted is a constant Current Driver. LEDs require a voltage to light, but it is the current that determines how bright the LEDs are. Yes you can hook up the 5V reference to power a pic. That is actually how the unit was designed. Then you can turn around and hook the output of your pic to the Ctrl Pin on the BuckPuck to pulse, or strobe the unit. The output of the Ctrl Pin is specified at 5V, 20mA maximum. In terms of power, the minimum input of the BuckPuck is 5V, while the maximum input is 32V. You can drive a single Luxeon III using anywhere from 5-32V. You will however notice the efficiency decrease, as the gab between the vf Load, and vf input increases. To drive a single LED I wouldn't recommend using more than say 18-20V. Don't get me wrong you can, but the BuckPuck just isn't going to be very efficient. For your application one LED and 12V you are all set.

LED Supply

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For all of your LED and LED Driver needs.

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zach

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