Found this circuit on the internet

Discussion in 'General Electronics Chat' started by mrel, Oct 17, 2015.

  1. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hello
    Found this circuit on the internet.
    I want to power up led that need voltage between 11 to 12 volts.
    The led can take up to 1.68 amp.
    Do anyone know if circuit will work with IRF 510 instead of IRF540.
    Anyone who know about circuit will this circuit?
    mrel
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    632
    Probably; the IRF540 would dissipate less power but the IRF510 should work, only dropping a little more than half a volt, and probably would not need a heatsink -that would depend on the thermal environment.

    Is your LED more than a bare LED or is it a LED lamp with some current limiting circuit so it can operate directly from 12 volts? If you provide a photograph or manufacture and part number we can check to see whether the LED is safe to use in this circuit.
     
  3. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Dick Cappels
    Enclosed is attach file of the led description.
    mrel
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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  5. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hi Dick Cappels
    I attach file for a current regulator will this work with the original circuit post earlier.
    not to sure r1 is correct valve of 1.2 ohm for this led 12 volts at 1.68 amp.
    Way i hook this regulator up ,part that say input attach 12volt the other end i hook the negative end from led to drain of the IRF 510.
    mrel
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    This a good and easy-to-use current regulator.

    With a 1.2 ohm resistor you will get about 1 amp through the LED array. Even thought the LED array is rated at 1.68 amps (Very strange to see current rating to 3 digits resolution), running it at a lower current will give you more lumens per watt and result in slower degradation of light output over time.


    I take it that you want the LED to come on when it is dark, in which case, you can connect it as you suggested.
     
  7. ISB123

    Well-Known Member

    May 21, 2014
    1,239
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    Use two 2.7R 15W resistors wired in paraller.
     
    Last edited: Oct 18, 2015
  8. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hi Dick Cappels
    In the first post drawing show a transistor 2n3906 in the circuit, do really need that transistor in the circuit,I pull that transistor(2n3906) out of the circuit the circuit still work when it is dark the led come on which i want the led to come on when it is dark.
    Do you know what the purpose having this transistor (2n3906) in the circuit?
    mrel
     
  9. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    Really bad title thread. Can you make it something descriptive?
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    The transistor adds hysteresis to the circuit, as noted in the drawing. Hysteresis is a type of positive feedback, and makes the circuit's response to slowly changing light levels much more abrupt. Without it, as the light level slowly decreases, the LED's brightness slowly increases. With the 3906 in the circuit, as the light level slowly decreases the LED stays off until the light level reaches a particular level called the trip point. Then the LED snaps on full brightness.

    ak
     
  11. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hi AnalogKid
    Since you seen this circuit in this thread post .
    Do know why when put 12 volts on the 2n3906 transistor emitter the Led would not turn off .
    Phototransistor in the circuit supposed turn on led on when no light on the phototransistor when dark,right now led stay on when put 12 volt on the transistor emitter.
    Could use help on why circuit not working right.
    mrel
     
  12. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    Replace phototransistor with switch and see if it works.
     
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