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Looking for a simple circuit for power regulation and led indicator light

Discussion in 'LEDs and Optoelectronics' started by pityocamptes, Nov 18, 2012.

  1. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Power intake will be from solar and testing it yesterday showed power fluctuations from 5 volts dc .85 amps to 3.5 volts .4 amps. due to clouds or more important its a non tracking system. The charging circuit I am using uses a chip that is only good until 5.5 volts. Can someone suggest or post a simple circuit that limits voltage (with little waste) to 5.5 volts maximum and controls two leds (one red and one green) - the green led will stay lit if the voltage stays above 3 to 3.5 volts and switches red if the voltage drops below 3 or 3.5 volts (haven't decided on a ceiling or floor voltage). Thanks!! Looking for a low voltage circuit option as the solar panels and charging unit will basically be powering the circuit.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    A 5V 10W zener should do the trick for clamping the voltage (it's wasteful).

    An alternative is one of the buck/boost regulators from eBay that would be able to take your 3.5 to 5.5 V input and turn it into a constant 5V (load dependant)

    As for turning LEDs on and off at different voltages, there are a number of voltage detector devices (three terminal devices) that will do this with no additional components. However, note that they're generally not adjustable, you order them with the switching voltage you required.
     
  3. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Thanks. I just ordered a cheap buck convertor from ebay. I guess what I am looking for now is a simple circuit that turns on a green led for input voltages lets say above 9 volts and if the source voltage drops below 9 volts the green led switches off and a red led switches on... any ideas?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
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    Jan 21, 2010
    A buck regulator can only reduce the input voltage. Are you sure that's what you want?
     
  5. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Actually yes. My original plan was to run buck/boost convertors directly from teg units run in series but after calculating loss from a small charging unit I figure now that I will run the units in series, reduce the voltage since I have more to work with and use the buck convertor to run the charging chip for super caps.

    Any thought on the led lights? Thanks again!
     
  6. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    On a conservative mind the LEDs for simple status indication are horribly wasteful, unless necessary...
     
  7. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I found this circuit. How would I change it so that green led was on for voltages above 12 volts, red for voltages under 9, and nothing for voltages inbetween? Thanks! Oh, also how would I calculate the resistor values in case I need to modify it? What does VR1 do?

    http://electroschematics.com/5397/three-state-voltage-indicator/
     
    Last edited: Nov 19, 2012
  8. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I know but it is sort of necessary for my project..
     
  9. BobK

    BobK

    7,609
    1,648
    Jan 5, 2010
    This looks like a classic case of voltage creep. You better hurry up and finish this project before you have to start dealing with dangerously high voltages...

    bob
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    I'm not sure I understand how that circuit can work.

    edit: this makes more sense. You can do a similar trick with the output to get a red/green LED, but it's pretty wasteful of power. Also ressitors either side of the pot will make the adjustment less critical. If you use a 10k trimpot, then I would have 10k resistors at either end. That will allow adjustment from about 7.5V to 15V
     
    Last edited: Nov 20, 2012
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