Dual stage LED driver for 70mA P4's

Discussion in 'The Projects Forum' started by DreyeIce, May 13, 2016.

  1. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
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    Hi, im working on a small lighting project. I need 3 circuits. 2 that simply turn on with 12V power and put a string of 3 LED's to 60mA, and one dual stage circuit that turns on 5 strings of 2 led pairs from 16mA to 60mA.

    Using 2.5v, 70mA Cree P4 leds, I have prototyped just a simple circuit with LM regulators and resistor strings, i have tried using an LM337 with a voltage divider on the ADJ/OUT pin, and i have tried the ON-Semi method of transistor controlled strings using a LM317T with my own addition of a 2n7000 mosfet to introduce another resistor in parallel to get dual stage.

    All have worked but i have been wanting something more efficient. Being the device is battery powered i dismissed the first 2 ideas (one with 7809 regulators, and the other using 5 LM337's) due to them being too hungry for use on a battery. The third idea is better, using only 3 LM317's in total, but still not quite there for me.
    Earlier i entertained the idea of using a 555 for PWM and controlling a TLC5947, but it only outputs about 30mA max, and i cant find anywhere if i can parallel mode 2 of the output pins to get 60mA like a few of the TI LED devices say.

    Any ideas? I can use eagle cad, and have a very god understanding of electrical. Just a little out of the loop for products/IC's on the market that can be used.
    I have attached my current plan. I put some other things on the same eagle file (will be on the board with other things in the end), the 7809 with the 150ohm is extra. Thanks.
     
    Last edited: May 13, 2016
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    You can't build one for the price of these:
    Just to make sure.....
    The dual stage has 2 currents 16 and 60 ma.
    It is 2 LEDs in series and another set of 2 in series with the first 2. Then 4 more sets the same. All 5 run at 16 or 60 ma.?
     
  3. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
    13
    0
    I figure that much for price.

    16 to 60mA is what I'm aiming for. See the initial larger circuit of the 7809 and the 317? On each output from the 317 there will be 2 leds in series on each string, to make up a 10 led array (5 outputs). I chose this just so there is an even number of leds on each string so the transistor circuit works properly.

    Reading it I see my initial explanation of "2 led pairs" is confusing. My bad.
     
  4. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
    13
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    Any more Input? Is my mosfet setup for each string ok for the components used?
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I think I would buy 2 of these little guys:
    http://www.ebay.com/itm/Boost-Buck-...952440?hash=item2ca0a868b8:g:0CAAAOSwLVZVs4ch
    We can then build you a simple constant current circuit for the 10 LEDs that we will put in series running off of about 30 volts. I don't see in your schematic what adjust the current. Is it a potentiometer or a micro or what?
    Then we can do the similar thing with the 6 LEDs.
     
    KJ6EAD likes this.
  6. DreyeIce

    Thread Starter New Member

    Nov 23, 2011
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    Each led string of the 10 when running would output 16mA based on the (should be) 78ohm resistor in series with each string. When 12V is applied to LSP11 post, the mosfet puts the 26ohm resistor in parallel with the 78 to get the 317 to output 60ma and brighten the setup.

    I actually just realized i drew it switched. The 78 should be always on in series, and the 26 should be introduced by the mosfet. That is the only way i could come up with to retain the transistor circuit to keep the 317 happy and introduce a dual stage. Still unsure if im using the mosfet correct though. The circuit shown is supplying 4.5V to the gate.
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe like this:
     
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