I did check one NUD4001, one set resistor 2 Ohms and one LED. It gives right current about 0.350 A. Soon as I do 2 parallel NUD4001 in order to get double current, I actually get 1/4 of current. I did follow data sheet instructions, I did make paraller circuti with LM 317 and it worked nice, double the current from one chip. It jsut doesn't work with NUD4001. I put 7 leds, 27V (3x9V battery), used 2 chips, 2 resistors 2 Ohm each and got .350A, not 0.7A.

 

What is the value of the DC voltage you are applying to the circuit?

It would seem the all you would need is one nud4001 set to produce 350 milliamps and connect your LED's in series. In this case you would need an input voltage of 7 or 8 volts.

hgmjr

 

It is not a problem with 1 chip. It is problem trying to reach .7A, what should be 2 chips parallel. Above test I just made to confirm that 1 chip with 2 Ohms set resistor will give me .350A. I used 9V battery with 1 Ohm 1W resistor in series with LED to make up for extra voltage.
So if 1 chip is giving .350A, than 2 chips parallel should give 0.7. But - NOT. I get lower, much lower current. Can it be because of bad PS, maybe not enough copper ( my boards were presintesised, but little bit old so I did have hard time making good board ( print on transparency, than expose board to UV)

 

If I understand your goal correctly, you are trying to drive each LED with 350 milliamps. That being true, then by putting the 2 LEDs in series the result will be that each of the LEDs will get 350 milliamps since the current will be the same through each one.

hgmjr

 

Few posts below you will find tread titled NUD4001 driver problems or something like that. That explains what I am trying to do in more details. I want to drive 1,2,3 leds ( in seris) eash of them uses 0.7A. Nud4001 can make no more than 0.5 A withou transistor. So I am putting 2 chips parallel to make 0.7 A. For some reason I am not getting 0.7 A. Rset is Ok ( 2 Ohms) volstage is OK for allleds in series + V sense, Power is ok. Can't find waht. I used datasheet,
I will try new one with Power transistor and Schottky diode, if it works, i wll add PWM, so I can have small light for head magnifier. Problem is I do not have too much time as I spand most of my time working on the field. This week was slow so I tried to make light I need, but ... Now I am interested in making it right and I will post results ( I am sure i will make it right, just have to find stupid mistake i am cought in.

 

hi hgmjr,

u were the one who steered me to this devices, and i got samples from onsemi. up to now i have not tried making a circuit using these. i have not also read the datasheets thoroughly. however the problem presented by "bobank" is quite interesting. he's trying to derive 700ma from the parralel chips w/c i believe he can have. i believe you have more indepth knowledge on this.

moz

 

Rather than using two NUD4001's you may want to build
a current sink circuit. The current sink consists of an
op-amp, MOSFET and a sense resistor. The amount of
current you can sink is limited only by your MOSFET.

I have a schematic in the "Load Schematic"
section of my document at ---

http://www.luciani.org/geda/util/matrix.pdf

(* jcl *)

---
www.luciani.org