Converting a small circuit to run from an outlet

Discussion in 'General Electronics Chat' started by aconz2, Feb 9, 2010.

  1. aconz2

    Thread Starter New Member

    Feb 8, 2010
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    Hello this is my first post so bear with me and tell me if I need to add anything.

    What I have is a circuit taken from a solar LED lawn lamp. It charges a single AA battery using a small solar panel which then lights two LEDs when it is dark using a sensor.

    What I want is to remove the solar panel and battery and just use a wall wart to power it. I have a 4.5V 100mA wall wart that i would like to use. I think i need to use a voltage divider using resistors to end up with 1.5V like the original circuit.

    What I have done is to replace the existing LEDs with a different color, but that shouldn't make a difference and I tested it with the battery and it worked fine. I removed the solar panel and battery. I made a voltage divider circuit using a 3.3KΩ and 1KΩ which should divide the voltage by 1/4 and that is attached to the wall wart. Well I tried attaching the circuit to the now divided wall wart and nothing happened but i measured with a multimeter and the voltage was the correct amount so I am stuck as to what is wrong.

    Any help would be appreciated. Thanks.
     
  2. przachar

    New Member

    Feb 8, 2010
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    Could you explain how the rest of your circuit is built? Did you check the voltage at various stages of the circuit?
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    Your resistors divide the voltage only when they do not provide an output current.
    They also divided the current so the LED circuit does not have enough current to operate.

    You could use a voltage regulator like an LM317 IC to regulate the output voltage to the circuit at 1.25V.

    Did you know that the LED circuit steps-up the voltage from the 1.25V battery to about 3.5V for the LEDs? The entire circuit can be replaced by a single resistor in series with each LED and powered from your 4.5V wall-wart. But then the LEDs will not have the circuit that turns them off in daylight.
     
  4. joemmech

    Member

    Jan 22, 2010
    32
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    do you have a schematic for this?
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The schematic for the LM317 1.25V regulator is shown in its datasheet. It needs an LM317, an input capacitor and an output capacitor.
     
  6. aconz2

    Thread Starter New Member

    Feb 8, 2010
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    Yes I am aware of that but I would like to keep the circuit that will turn it off in the daytime. Would eliminating the part of the circuit that ups the voltage and then running the entire circuit off of 4.5V be harmful to any of the components?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You would need to reverse-engineer the circuit to remove the parts that increase the voltage. Use an LM317 voltage regulator to power the entire circuit from 1.25V.
     
  8. aconz2

    Thread Starter New Member

    Feb 8, 2010
    16
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    Thanks for the advice and one last thing, do you think I will need an extra heatsink for the LM317?
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    The solar garden light uses such a low amount of power that the LM317 will not get warm.
     
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