# Thread: EE question for a non EE...(Buckpuck fctn)

1. ## EE question for a non EE...(Buckpuck fctn)

Since ordering this Buckpuck, I was pondering how the crap it works. I can plug a bunch of emitters in series into it and just run higher voltage than the collective series requirements.

Ex: I'm running a 2s XP-G setup, so I need to use 11.1v LiPo pack. From what I understand though...I could in theory plug my 18v Ryobi pack into the thing and it will still "buck" the voltage and only deliver what the string requires.

How does it know how much voltage to deliver? How does it sense it?

2. Current (hint) regulated drivers don't sense the "voltage to deliver", they provide a constant current to the load.

So, as long as you run them within spec (don't exceed max input voltage) and you have at least a volt or two (depends on the headroom requirement) they will provide a constant current to the load. The output voltage therefore will adjust as needed to maintain that constant current...

cheers,
george.

3. I understand that.

My question is...how does the output voltage adjust. Does the current draw dictate the output voltage?

I believe the max input voltage for the Buckpuck is some crazy 32v. But if I'm running just one single XP-G that requires only 3.7'ish volts...how does it know to only deliver that voltage? If I run two LED's in series...it's still only 1amp...but twice the voltage. I don't quite understand this stuff yet.

4. It works just like I said - the driver is current regulated, therefore it will adjust the output voltage as needed to maintain the selected current flowing through the load.

It really is no different than a voltage regulator - how does it maintain a constant voltage regardless of the load current? Just flip that question on its head and you have the equivalent question for a current regulator... how does it maintain a constant current regardless of load voltage?

Essentially a current regulator has a small sense resistor (fraction of an ohm) that is in series with the output load. The regulator measures the voltage across that sense resistor and it will adjust output voltage as needed to maintain a constant voltage across the sense resistor. Since the resistor is a constant and V = I x R, if you have a constant voltage across the sense resistor then you must have a constant current flowing through it AND the load...

There's always google for more detailed explanations....

cheers,
george.

5. Excellent...I can live with that.

Thx george.

6. I can't say how it works, just that it does work....very easy. As long as you have at least 2v over what your LEDs are looking for. If the voltage drops too low I assume it goes to direct drive. you lose the dimming ability, but you still have light...no surprise shut off.

7. the drivers are full of magic smoke. be careful not to let it escape

8. I was thinking fairy dust.

9. Originally Posted by slidecontrol
the drivers are full of magic smoke. be careful not to let it escape
This is true!
I hooked up one of taskled's drivers backwards and it caused the magic smoke to escape.
It stopped working until I sent it back to george so he could fill it back up.
Now it works fine.

10. Yeah, I, too, realised way too late in life that instead of getting a degree in graphic design, it was electrical engineering the whole time. Better pay, more work, understanding how a current regulator works, etc.

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