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Homework Help: Solar panel tester circuit?I really need help

  1. Nov 12, 2008 #1
    hey there..
    I was asked to design a circuit using multisim software of a solar panel tester..
    I know I need an operational amplifier.. a diode pehaps..
    but I don't have a background concerning the way operational amplifiers work...

    The lecturer wants us to construct this kind of circuit:

    "The Tester consists of four levels of LEDs voltage display, Red, Orange, Yellow and Green.

    1. The tester will show all the LEDs lighting up when the voltage of the Solar Panel is 6V.

    2. When the voltage of the Solar Panel is 5V, the Red, Orange and Yellow LEDs will light up.

    3. When the voltage of the Solar Panel is 4V the Red and Orange LEDs will light up.

    4. When the voltage of the Solar Panel is 3V, only the Red LED will light up.

    5. When the voltage of the Solar Panel is less than 3V no LED will light up."

    I don't know where to start..I can't find till now useful information to helpme construct such a circuit on multisim... can ne1 help by atleast giving me the way to start?
  2. jcsd
  3. Nov 12, 2008 #2


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    It sounds like you need to build some voltage comparators (which are implemented using op amps). Comparators, as their name suggests, compare voltages. More specifically, they have two inputs. One input is tied to a reference voltage (which is the voltage being compared TO). The other input is the variable voltage level that needs to be compared to that reference. If the test input is less than the reference, then the output of the voltage comparator is at a certain level (let's say low). On the other hand, if the test input is greater than the reference level, then the output of the comparator is the opposite (let's say high). Therefore, you need four voltage comparators, one for each reference level. The output of each comparator can drive the LED in question. You can easily generate the reference voltages using a resistor voltage divider.

    Does that help? The rest you can do by researching how a voltage comparator works (and how to build it using an op amp).
  4. Nov 12, 2008 #3


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    I just did some quick checking and it looks like a comparator is just about the simplest application of an op amp there is. You don't have to build much of a circuit around the amplifier...you just use it open loop.
  5. Nov 13, 2008 #4
    Thanx a lot cephied...
    u really helped .. I appreciate all ur effort a lot..
    I'll try then to search more about how a voltage comparator works..I think I'll need 2 use 5 comparators ..
    I'm just a begginer in these stuff, that's y it's kind of difficult for me ..
    Thanks again :)
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