# LM675 non-inverting gain amplifier not working

#### eetech00

Joined Jun 8, 2013
2,644
It is not at 1/2 of the supply voltage. It is at:

$$\dfrac{Vcc\;+\;Vee}{2}\;\approx\;0$$

We have a bipolar supply of ±18 or ±24 depending on which simulation you're looking at. The input is biased at approximately DC ground. That is because the input signal is supposed to be 5.4 VP-P or ± 2.72 V. The input signal coming from an Arduino is 0-5.4 V and so AC coupling is indicated. It does take a few cycles for the input to get to it's steady state level, but I'm thinking that this is a minor concern. Certainly you would not want to have a 5.4V signal going into an amplifier with a gain of 21.
Thank you...

#### Papabravo

Joined Feb 24, 2006
17,245
Hello,

There are two parameters that will influence the output.
The GBW and slewrate:
View attachment 247260
The slewrate will limit the maximum frequency for the square wave.

Bertus
The measured slew rate in the simulation was 7.25 V/μsec which is IMHO in good agreement with the datasheet. Since we have discrete time steps in a simulation, accurate measurements on waveforms can be difficult to achieve. I think the problem here is mostly in the slew rate limitation.

The TS has stated that the prototype he has constructed still does not work at low frequency. In the simulation the output looks more like an amplified replica of the input than it does at higher frequencies. I believe that the reference circuit from the datasheet will work at low frequencies in the absence of wiring, component, and construction errors.

#### Audioguru again

Joined Oct 21, 2019
3,833
Since the amplifier does not work at a low frequency then the IC, a resistor or the wiring is defective.