# Drawing the DC Model of a Circuit

1. Mar 7, 2015

### KTiaam

1. The problem statement, all variables and given/known data

[Picture of Problem](http://i.imgur.com/7q4yj8O.png)
2. Relevant equations

* It is dealing with drawing the DC model of a circuit
* Now i know when drawing a DC Model, all capacitors are open (or ground) and AC sources are grounded as well.
* In this specific problem, i know that the left most OP-Amp is a Voltage follower, meaning that i can just disregard that OP-Amp, and connect a wire form pin 3 to pin 5 and treat it as just a wire connecting those two pins.
* The second OP-Amp on the right is going me trouble, however. Pin 6 goes straight in to a capacitor (C2) which is ground. So does that mean that the OP-Amp does not exist?
* Also from my understanding R3 does not exist, because both ends of the resistor are connected to ground. Also if my logic is right about R3, then R1 does not exist.
* At this point any help is appreciated.

2. Mar 7, 2015

### Staff: Mentor

At DC capacitor C1, C2, C3 each represents an open circuit.

3. Mar 7, 2015

### Staff: Mentor

Not really. An op-amp as a voltage follower also provides isolation. Pin 3 should never "feel" anything that happens to pin 6 (I think you meant pin 6, the output of the op-amp). And pin 6 should not be able to "see" the impedance at pin 3. You want to just declare the voltage at pin 6 to be whatever the voltage is at pin 3.
Not at all. The capacitor is an open circuit at DC.
C2 and R3 effectively don't exist at DC. But R1 most certainly does.