I'm trying to reduce the input voltage into an opamp from about 15 to 4. I have mocked a circuit up and it kinda works but I want to understand the math better. It is wired up to be a differential opamp for current sensing.
How I wired it up is with 2 1.6k input resistors, then 2 46k a feedback resistors, one I to ground the a other I to the inverting input. Then I added two more resistors to ground on a the inputs creating effectively a voltage divider. This seems to work, however in spice simulations adding these two resistors increases the gain. I want to be able to calculate the gain, but when I add these resistors the gain is tweaked just a little bit. It would be amazing if someone could point me at some info, I'm sure it's simple but I can't grasp it. I'm trying to write this on a cell phone, so I can add a diagram later if that is necessary, and I apologise for the rampant auto correct, is it's there.
How I wired it up is with 2 1.6k input resistors, then 2 46k a feedback resistors, one I to ground the a other I to the inverting input. Then I added two more resistors to ground on a the inputs creating effectively a voltage divider. This seems to work, however in spice simulations adding these two resistors increases the gain. I want to be able to calculate the gain, but when I add these resistors the gain is tweaked just a little bit. It would be amazing if someone could point me at some info, I'm sure it's simple but I can't grasp it. I'm trying to write this on a cell phone, so I can add a diagram later if that is necessary, and I apologise for the rampant auto correct, is it's there.