0
\$\begingroup\$

i have a question about this circuit

enter image description here

the inverting input is connected to ground , so any voltage different than 0 in the non inverting input will saturate the op amp ( correct me if i'm wrong). how can this circuit work without feedback ?

\$\endgroup\$
  • \$\begingroup\$ Where did the circuit come from? \$\endgroup\$ – Colin Jan 24 '18 at 12:50
  • \$\begingroup\$ @Colin__s it is the same as the application diagram in the datasheet. \$\endgroup\$ – Bimpelrekkie Jan 24 '18 at 12:51
  • \$\begingroup\$ Any opamp without NFB is fairly useless(except perhaps as a comparator). Fortunately this is not an opamp (and it has NFB internally). \$\endgroup\$ – Brian Drummond Jan 24 '18 at 12:53
  • \$\begingroup\$ @Bimpelrekkie that's why I wondered. If it's from the datasheet this question was already answered. \$\endgroup\$ – Colin Jan 24 '18 at 12:53
  • \$\begingroup\$ Picture from google, I typed audio amplifier \$\endgroup\$ – Mourad Jan 24 '18 at 12:55
7
\$\begingroup\$

The LM386 has feedback and it sits inside the chip.

As opamp's generally do not have overall feedback (local feedback can be present though), the LM386 clearly is not an opamp, it's an audio power amplifier.

Open the datasheet and on the first page you see the internal schematic:

enter image description here

These's a 15 kohm resistor which is part of the feedback circuit together with the 150 ohms and 1.35 kohm resistors.

Never assume an IC's function from its symbol, all amplifiers (can) use a triangle shaped symbol, it is not reserved for opamps. Instead, read the datasheet so you know what it is (instead of guessing/assuming).

|improve this answer|||||
\$\endgroup\$
10
\$\begingroup\$

The LM386 is not a opamp. It is a power amp with a fixed gain of 20. This is, of course, all very clearly spelled out in the datasheet.

Right on the first page:

|improve this answer|||||
\$\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.