0
\$\begingroup\$

I'm using this TL071 op-amp datasheet and I am trying to find the op-amp output impedance on the datasheet so I can calculate the output impedance when used in amplifier/peak detector circuit. Do I need to calculate the output impedance from one of the other characteristics on the data sheet or am I missing something?

Many thanks in advance!

\$\endgroup\$
5
  • \$\begingroup\$ You really shouldn't be using a 741. \$\endgroup\$ – Hearth Apr 4 '20 at 17:52
  • \$\begingroup\$ Sorry, just edited its a TL071, to be used in a peak detector circuit. \$\endgroup\$ – arry_h Apr 4 '20 at 17:53
  • \$\begingroup\$ Oh, much better choice. \$\endgroup\$ – Hearth Apr 4 '20 at 17:55
  • 1
    \$\begingroup\$ You realize that when applied in a closed loop, the output impedance is usually less than an ohm across a broad range of operating frequencies. \$\endgroup\$ – Andy aka Apr 4 '20 at 17:57
  • \$\begingroup\$ Thank you for all the responses. Yeah I now realise, when implementing it practically, I shouldn't consider it too much - thanks again. \$\endgroup\$ – arry_h Apr 4 '20 at 18:01
2
\$\begingroup\$

You won't find it if it's not explicitly listed (which is rare). Typically Zo of the order of a hundred ohms for that type of op-amp.

Closed loop output impedance, of course, is almost zero.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Many thanks for your answer, Sir. \$\endgroup\$ – arry_h Apr 4 '20 at 18:03
0
\$\begingroup\$

The output impedance in a closed loop situation will increase with frequency because as frequency increases the feedback reduces. The feedback factor in an amplifier, for instance, is equal to 1 + BAo and as frequency increases, the open loop gain,Ao rolls off. You could say that the output impedance is simulating an inductance which also has an increasing impedance with frequency.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.