Load seen by opamp

Hi,
1)If i use an opamp with resistor feedback (for example in inverting
configuration with gain -R2/R1), the output resistence seen by opamp
is one resistor of R2 value?
2)for an opamp used in noninverting configuration (with gain 1+R2/R1),
the output resistance seen by opamp is R1+R2?
Thanks in advance

 

[John Fields]

On Sat, 25 Oct 2008 02:33:04 -0700 (PDT), silusilusilu@gmail.com wrote:

Hi,
1)If i use an opamp with resistor feedback (for example in inverting
configuration with gain -R2/R1), the output resistence seen by opamp
is one resistor of R2 value?

---
Yes
---

2)for an opamp used in noninverting configuration (with gain 1+R2/R1),
the output resistance seen by opamp is R1+R2?

---
Yes.

JF

 

[Bob Eld]

<silusilusilu@gmail.com> wrote in message
news:f4a7253c-23a8-4b24-8b2a-22806bb35394@p49g2000hsd.googlegroups.com...

Hi,
1)If i use an opamp with resistor feedback (for example in inverting
configuration with gain -R2/R1), the output resistence seen by opamp
is one resistor of R2 value?
2)for an opamp used in noninverting configuration (with gain 1+R2/R1),
the output resistance seen by opamp is R1+R2?
Thanks in advance

True if nothing else is connected to the op-amp output. Of course, what is
an op-amp circuit for if not to drive other circuitry? Technically this is
the not the "output resistance" but rather the load resistance. The output
resistance is internal to the op-amp and has a low ohmic value. That low
value is further reduced by the loop gain of the amplifier with feedback.

 

[Eeyore]

silusilusilu@gmail.com wrote:

Hi,
1)If i use an opamp with resistor feedback (for example in inverting
configuration with gain -R2/R1), the output resistence seen by opamp
is one resistor of R2 value?

Excluding the external load, yes.

2)for an opamp used in noninverting configuration (with gain 1+R2/R1),
the output resistance seen by opamp is R1+R2?
Thanks in advance

True with the same caveat.

Graham