# Help with this circuit

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

1. ### supra Thread Starter New Member

May 11, 2012
1
0
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
9,411
896
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.
Simple.

3. ### lll New Member

Mar 7, 2012
21
1
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
1,426
364
I see no LED here. There is a reverse biased zener diode though.