# CE amplifier

#### hamza324

Joined Jul 10, 2011
33
hi i have a basic question related to op ams.

In circuit analysis of op amps.....when is it possible to ignore the $$r_o \ (output \ \ resistance)$$

for calculation of $$R_L$$

because in some of the problems i solved for CE amps ......$$r_o$$ was included during some of the problems and it was ignored for some problems in calculation of $$R_L$$
Thanks

#### crutschow

Joined Mar 14, 2008
27,242
hi i have a basic question related to op ams.

In circuit analysis of op amps.....when is it possible to ignore the $$r_o \ (output \ \ resistance)$$

for calculation of $$R_L$$

because in some of the problems i solved for CE amps ......$$r_o$$ was included during some of the problems and it was ignored for some problems in calculation of $$R_L$$
Thanks
$$r_o \ (output \ \ resistance)$$ is reduced by the loop gain in a op amp with negative feedback, so for practical values of circuit and op amp open loop gain it typically is negligible. If you use the op amp in an open loop or positive feedback application, then you may need to consider it.

#### Audioguru

Joined Dec 20, 2007
11,249
The output resistance of an opamp reduces the max peak output voltage when the load current is fairly high.
An output resistance of 100 ohms reduces the max peak output voltage 2.5V when the max peak output current is 25mA.