Led driver NUD4001 problems - need help

Thread Starter

bobank

Joined Nov 19, 2005
21
I just made board for 2 luxeon REBEL lights using NUD4001 driver. I used 2 NUD4001, connect them parallel and use 2 Ohm 1/4W set resistor what should give 0.350A per each, as they are parallel, current of 0.700A should go through both REBELS ( they are conneterd in row). But when I measure current it shows about 0.17 A, I made second one and it shows the same current. It must be some stupid mistake that I just can't see.
 

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Thread Starter

bobank

Joined Nov 19, 2005
21
Forgot to say Voltage is 9V ( for 9V battery), but I tried higher voltage on my power suply and sowed the same current.
BobanK
 

Papabravo

Joined Feb 24, 2006
13,471
The application circuits in the data sheet show a series resistor when the drivers are used in parallel to account for the differnece in voltage drop between the 9V source and two forward voltage drops in the two LEDS. You seem to have forgotten this detail.
 

mrmeval

Joined Jun 30, 2006
833
You are using two chips to drive two LEDs. What is the current needed to drive one?

There is an example in ON's documents of a single chip running three 350ma diodes in series.
 

Thread Starter

bobank

Joined Nov 19, 2005
21
Papabravo. 2 leds 3.6V each is 7.2 + Vsense(0.7V) = 7.9V - 7.9 = 1.1 what is little bit below of Vdrop, so I do not need series resistor, if this is what are you talking about.
Mrmeval, I want to drive 0.7A each led. Nud4001 is good for 0.350 ( with resistor of 2 Ohms. Still do not see the problem. Please, keep trying, I just lost 2 days making so far 30-40 boards. I made one tonight, but still didn't check it, with single LED and single NUD 4001. That one has Resistor in series of 1 Ohm and 1 wat. to make difference bet, 9V and 3.6V. I will connect it tomorrow ans see if I am getting, this time 350mA.
Thanks
Boban K
 

JoeJester

Joined Apr 26, 2005
4,259
bobank,

Can I assume you downloaded the design spreadsheet?

The manufacturer's site has two different design spreadsheets and it should not be a problem to do what you want.
 

Thread Starter

bobank

Joined Nov 19, 2005
21
Do you mean datasheets? I did follow direction on datasheets. What is spreadsheet and where to find it?
Thanks
BobanK
 

JoeJester

Joined Apr 26, 2005
4,259
Go to http://www.onsemi.com and search for the Part Number.

The results will show 13 matches. Select the "Supporting Tech Materials" tab. The first two are design spreadsheets ( xls format ). You plug in your numbers and it will provide you with the values and which circuit configuration to use.
 
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