inverting or non-inverting input?

bassk81976 · Post by **bassk81976** » 04 Aug 2010, 03:03

what's the difference between the two for an ic like the lm386 or the lm4562?

earthtonesaudio · Post by **earthtonesaudio** » 04 Aug 2010, 12:19

Those are two very different ICs.

The LM386 has internal feedback and biasing networks so that the inputs are ground referenced and the gain is fixed at 20. The other is a more general purpose op-amp which means the input bias and gain need to be set externally.

Basically you just need 3 bits of information to understand (ideal) op-amps:

1. The inputs draw no current
2. Through the use of feedback, the output does whatever is necessary to make the inputs equal.
3. The output follows the (+) or non-inverting input and does the opposite of the (-) or inverting input.

briggs · Post by **briggs** » 04 Aug 2010, 23:02

What's the difference how? Bias? Gain? Freq Response?

bassk81976 · Post by **bassk81976** » 04 Aug 2010, 23:30

yea, i knew the two chips were vastly different, i listed them as examples because the have a common thread - an inverting and a non-inverting input pin. I just don't know the difference. Phase shift?

earthtonesaudio · Post by **earthtonesaudio** » 10 Aug 2010, 16:05

In very general terms, when the signal at the non-inverting input goes up, the output goes up. When the signal at the inverting input goes up, the output goes down.

What's the difference how? Bias? Gain? Freq Response?

General purpose op-amps have very high (ideally infinite) open-loop gain and need external components to set gain. The LM386 has its gain set by internal resistors. Also, most op-amps need their inputs biased by external components, but again the LM386's inputs are internally biased near ground.