Hi all,

Can someone explain the effect of a capacitor on the output of an op-amp? Will it behave like an RC circuit because of the resistor inside of the op-amp or something else?

Thank you in advance!

 

Hi sE,
Welcome to AAC.
It will act like an RC circuit, RC = output impedance of the amplifier and capacitor.
It will also reduce the high frequency output.
E

 

Welcome to AAC!

It would be helpful if you posted a schematic showing RC configuration, with values, that you're curious about.

 

Hi sE,
Welcome to AAC.
It will act like an RC circuit, RC = output impedance of the amplifier and capacitor.
It will also reduce the high frequency output.
E

Got it! Thank you

 

A capacitor to ground at the output of an opamp will cause it to oscillate at a high frequency if it causes enough phase shift for the negative feedback to become positive feedback.
The datasheet of most opamps show it working but almost oscillating with a 100pF capacitance. Most preamps use a series output resistor of 100 ohms to isolate the opamp output from the capacitance of a shielded output cable.

 

What about if you want to make a High pass filter coming from the output of an op-amp, would you put a 100-ohm resistor in series with the filter?

 

Most opamps can not drive a 100 ohms resistor, because at operating frequencies (below 10's of kHz)the current will be much too high.
The minimum load for most opamps is 2k ohms but a few can drive 600 ohms.

A highpass filter is best at the input of a non-inverting opamp because at the input, the input biasing resistor is high and the capacitor can be small.

 

Hi all,

Can someone explain the effect of a capacitor on the output of an op-amp? Will it behave like an RC circuit because of the resistor inside of the op-amp or something else?

Thank you in advance!

It depends on where you connect the other end!

 

Most opamps have an output resistance of about 75 ohms but negative feedback causes the output impedance to be almost zero ohms. The additional phase shift caused by an RC filter at the output causes oscillation.