Help with this circuit

Discussion in 'Homework Help' started by supra, May 11, 2012.

  1. supra

    Thread Starter New Member

    May 11, 2012
    Hi, I was hoping someone could help me with the following circuit. Does anyone know what this circuit is? I need to calculate the output current.


    Low voltage regulator??
  2. Audioguru

    New Member

    Dec 20, 2007
    The opamp is connected as a follower so its output voltage is exactly the same as its input voltage.
    Do you agree that its input voltage is +5V?
    Then use Ohm's Law to calculate the output current.
  3. lll

    New Member

    Mar 7, 2012
    When the output is fed back into the negative terminal like that, it is called a unity gain buffer amplifier, or just buffer amplifier. So the voltage at the (+) terminal is the same as the output voltage.

    Not sure how your class treats LED's, but mine treated them like a voltage source. The flat side of the triangle is the positive end of the LED, and the pointed side of the triangle is negative, so the voltage in the (+) terminal of the op amp is -5 Volts (remember, the voltage across the 10k resistor connected to the (+) terminal is 0 because almost no current flows into the op amp terminals).

    So the output voltage is also -5 volts since the (+) terminal voltage of a buffer amplifier is the same as its output voltage. And then you just use ohm's law to find the current.
    Last edited: May 14, 2012
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
    I see no LED here. :rolleyes: There is a reverse biased zener diode though.