Recognitions:
Homework Help

## op-amp circuit help

You may be under a misunderstanding that the only voltage source in the circuit is Vcc. That would be quite wrong. Not shown in many schematic diagrams are the + and - DC supplies powering the op-amp itself.

The Vcc shown serves to supply current to the zener diode. What voltage do you expect to find at the junction of the two 10k resistors and the zener diode?

Bearing in mind what you said about the horizontal 10k resistor, deduce the voltage that you would expect to measure on the right hand side of that horizontal 10k resistor (i.e., as measured at the inverting input (-) of the op-amp).

 V1 and V2 my lecturer kind of gave us an idea that there both 15 V and Vcc is 10V now im more confused
 Recognitions: Homework Help The voltages powering the op-amp do not dictate the output voltage of the op-amp, meaning you can largely ignore those voltages---which is why they are not even shown on some circuit diagrams. What is important is that the output voltage of the op-amp is controlled by the input voltages of the op-amp.
 then lets calculate the current..?
 Recognitions: Homework Help I framed some leading questions in post #18. Still waiting to see your answers. I'll be away, may not be back on for 3 or 4 days.
 5 V? we said the horizontal 10k would be 0 V

Recognitions:
Homework Help
 Quote by moe619 5 V? we said the horizontal 10k would be 0 V
Right. So how to determine the op-amp's output voltage? Remember, it's nothing to do with Vcc, providing Vcc is sufficiently high.

 the output voltage of the non-inverting amplifier is in phase with the input voltage. Vout=Vin

Recognitions:
Homework Help
 Quote by moe619 the output voltage of the non-inverting amplifier is in phase with the input voltage. Vout=Vin
Meaning Vout would be how many volts?

 5V? more or less?

Recognitions:
Homework Help
 Quote by moe619 5V? more or less?
Let's suppose the op-amp has an open loop low frequency differential gain of 10,000. Can you determine Vout exactly?

 approximately V out can be determined there is a formula but its for a summing/difference amplifier Vout= -(V1 + V2) (for unity gain mode) Vout= -(Rf/R) (V1 + V2) (where R1=R2=R) ...................... Vout= V2 - V1 (for a unity gain amplifier) Vout= (Rf/R1) (V2 - V1) (for an amplifier with gain where R1=R2 and Rf=R3
 Recognitions: Homework Help At seeing the word exactly I thought you may have applied this formula: Vout = A (V₊  ̶ V₋) But 5V is close enough. So with an output voltage of 5V, how much current is flowing in the load resistor? I believe that is what you are asked find?
 Vout = A (V₊  ̶ V₋) never seen this formula is it the same as Vout=Av*Vin V=IR 5=I x 10k I= 0.0005 A

Recognitions:
Homework Help
 Quote by moe619 Vout = A (V₊  ̶ V₋) never seen this formula is it the same as Vout=Av*Vin
The op-amp triangle shows two inputs. What is Vin?
 V=IR 5=I x 10k I= 0.0005 A
That looks right.

 Tags electrical circuits