Driver for power leds

Discussion in 'The Projects Forum' started by ctwistedpair, Sep 21, 2013.

  1. ctwistedpair

    Thread Starter New Member

    Jan 14, 2013
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    I am building a light string for use on a Clear lexan canoe. The string of leds will be shining down into the water at night for viewing the lake at night. I have 6 strings of 1watt 350 mA leds. 3 leds in series.
    What type of voltage regulator will handle the amperage for each group of three? It will be powered by a deep cycle 650amp deep cycle marine battery.

    Thanks for your help.
     
  2. #12

    Expert

    Nov 30, 2010
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    You don't use a voltage regulator for LEDs. You use a current regulator.
    12 ohm resistor at 3 watts (minimum) per string of 3 LEDs.
     
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  3. wayneh

    Expert

    Sep 9, 2010
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    You should look for a pre-built LED controller that matches your needs. They are quite cheap these days and will probably include nice features like dimming.
     
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  4. #12

    Expert

    Nov 30, 2010
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    I feel an objection coming on. Which LED controller has 6 channels?

    Lacking a pre-built, 6 channel dimmer, you could use a pre-built one channel PWM dimmer, if you wanted to dim the lights, but you will still need the resistors.
     
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  5. wayneh

    Expert

    Sep 9, 2010
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    Guess I should have read better. Yeah, a resistor on each series string is the right solution.
     
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  6. ctwistedpair

    Thread Starter New Member

    Jan 14, 2013
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    I have 3 watt resistors in each string, but I want to make sure that the current doesn't change as the battery charge changes. Too high or too low. High will smoke the leds, right?
     
  7. ctwistedpair

    Thread Starter New Member

    Jan 14, 2013
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    I would also prefer to build my own pwm. I etch my own boards now so this would be a good learning experience.

    Thanks
     
  8. #12

    Expert

    Nov 30, 2010
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    I already designed this to work properly with up to 12.77 volts from the battery. Why do you think that will cause the LEDs to die?

    If you want to build a PWM circuit board, that is a different thing. Do you have a circuit in mind or do you want to start with this and change it to fit your needs?
     
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  9. wayneh

    Expert

    Sep 9, 2010
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    Right, one problem with the simple approach is that you must design for the highest voltage - to protect the LEDs - and then live with LED brightness at the lowest voltage.

    But, the proper operating range for a 12V battery is not so wide, and I think you would see a barely perceptible loss of brightness as the battery drains. A constant-current DC-DC converter can solve this problem but at the expense of ...expense, and a loss of simplicity. For a canoe, I'd choose simple.
     
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  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  11. abhaymv

    Active Member

    Aug 6, 2011
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    You could use an LM317 as a current regulator to power the LEDs. Such a circuit will limit the current to your required value. However, for 350 mA you'll need 3.57 ohm resistor.
    This circuit is fairly easy. In fact, I've done it. I think you'll find the circuit in one of the LM317 datasheets.
    To dim the LEDs here, you'll have to use a 10 ohm or 20 ohm pot.



    Alternatively, you can use six HV9910 ICs, one for each string. These PWM drivers are dimmable, so you can dim the LEDs.
     
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