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LM317 i problem z uzyskaniem 1A dla Power Led

smithpl 26 Kwi 2009 22:02 5158 11
  • #1 26 Kwi 2009 22:02
    smithpl
    Poziom 15  

    No właśnie,
    wykonałem na szybko układ oparty na LM317T jako źródło prądowe 1A
    aby do testów zasilać Power LEDy Q5 o poborze max. 1A.
    ( Zgodnie z notą aplikacyjną do LM317 )

    Niby wszystko działa ale martwi mnie uzyskanie tylko 0,65A.
    Rezystor dobrałem wg. opisu - wyszło mi 1,35ohm.

    Jednak przy tym rezystorze uzyskuje tylko 0,65A

    Układ zasilam z zasilacza 12V 2A ( prąd stały )
    na wyjściu podłączone są 3 power LEDy szeregowo. ( docelowo będzie 5 power LEDów )


    Dzięki za pomoc.

    0 11
  • #2 26 Kwi 2009 22:11
    jony
    Specjalista elektronik

    Podłącz jedną diodę i zobacz czy prąd nie wzrośnie. (Rezystor 1.2Ω/2W)

    0
  • #3 26 Kwi 2009 23:02
    smithpl
    Poziom 15  

    OK, a jak wzrosnie ?

    gdzie szukac problemu ?

    0
  • Pomocny post
    #4 26 Kwi 2009 23:51
    Ronin64
    Poziom 35  

    Prawdopodobnie w zbyt niskim napięciu zasilającym.

    0
  • Pomocny post
    #5 27 Kwi 2009 08:25
    Dar.El
    Poziom 40  

    Witam
    Potrzeba 2,5V na LM317, aby dał 1A. Docelowo potrzeba 5x3,5+2,5=20V na wejściu stabilizatora.

    1
  • #6 27 Kwi 2009 10:32
    smithpl
    Poziom 15  

    Super, dzięki za pomoc.

    0
  • #7 27 Kwi 2009 14:15
    HackoBoy
    Poziom 9  

    before many months i build this circuit
    Link

    in my case i use LM317 , Q1 = bc337 , r1 = 2 k , r2 = 2,2 k , pot = 4.7 k , C = 47 uF , r3 = 0.8 r

    use this circuit for my luxeon LXHL-LW3C - drive with 3.75 V / 1000 mA = supply circuit just ac/dc adapter ( 7,5 V / 1000 mA ) work well with 6,5 V up to 12 V ( for this moment i don`t test with more voltage )

    i give info :

    R3 is the "sense resistor" for the current-limiting circuit. select the value of R3 as follows: R3 = 0.55 / (LED string current). so for my circuit I have R3 = 0.55 / 0.8 = 0.69 ohms. resistors don't come in every possible value, the closest match was 0.68 ohms. you also need a resistor that can handle a bit of power, use this guideline:

    Selecting R4 control slider/dial
    First choose if you want a slider or dial! this is your user interface for your controls. It's less work to make a control panel using dials, because you just drill a hole for them, but you might prefer the look & feel of the sliders. I went with the sliders, but you'll see how much of a hassle they were later. any dial or slider between 2k-ohm and 10k-ohm will work. a 2k-ohm is the best because it allows precise calculation of the output voltage without testing. for sliders, i was only able to find 10k-ohm sliders which required a bit of trial-and-error to get the output voltages correct.

    Setting R1 and R2 control range resistors
    The combination of R1, R2 and R4 set the output voltage (= LED brightness) of the regulator. the output voltage is approximately equal to: 1.25 * (1 + ((R2+R4) / R1)). This becomes less accurate with larger R values. With a 2.5k dial for R4, the formula will be very close, with a 10k dial, you'll need to hand-test your R1, R2 values. below i work through two examples: one with 10k slider and one with 2.5k dial.

    0
  • #8 05 Maj 2009 12:26
    smithpl
    Poziom 15  

    HackoBoy thanks for information. Unfortunately in Poland is not a simple to find LD1585CV ADJ.

    Thanks for info about LM317 - it works :-)

    0
  • #9 05 Maj 2009 22:55
    HackoBoy
    Poziom 9  

    If you use this IC LM317 - you too hot, you better change it to this LM1084IT-ADJ
    difference is that the lm317 is 1 Amp, but LM1084IT-ADJ is 5 amps - which means that less will be shipped integrals.

    0
  • #10 05 Maj 2009 23:15
    smithpl
    Poziom 15  

    Exactly, I see LM317 and resistor 5W are so HOT.

    I'm looking for IC which will be easy available in Poland and I will be able to make normal drive 1A.

    PS. I will try to replace LM317 on LM1084IT-ADJ

    0