### Author Topic: Non-inverting op-amp question  (Read 3018 times)

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#### hazzer123

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##### Non-inverting op-amp question
« on: August 08, 2007, 01:57:09 AM »
I need to amplify a signal that varies around the range 2.4-2.6 volts, so that it outputs 0 - 5V.

I understand the basic circuit where the gain is 1+ (R2/R1), but i want an offset, where 2.4V into the V+ pin creates 0V on the output pin (and vice versa with 2.6V in = 5V out).

Any one have any ideas?

My op-amp has no balance pins.
« Last Edit: August 08, 2007, 02:16:53 AM by hazzer123 »
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#### Soeren

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##### Re: Non-inverting op-amp question
« Reply #1 on: August 08, 2007, 06:05:56 PM »
I need to amplify a signal that varies around the range 2.4-2.6 volts, so that it outputs 0 - 5V.

I understand the basic circuit where the gain is 1+ (R2/R1), but i want an offset, where 2.4V into the V+ pin creates 0V on the output pin (and vice versa with 2.6V in = 5V out).
So, you need a gain of ((5-0)/(2.6-2.4)) = 25, with an offset of -2.4V.

The offset will also see the amplication factor, so you need to add an offset of only -2.4/25 = -96 mV.

Since it's a negative numbe, easiest way is to lift your inverting input by 96 mV (since inverting a minus yeilds positive).

Regards,
Søren

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##### Re: Non-inverting op-amp question
« Reply #2 on: August 09, 2007, 07:30:40 PM »
Another method Ive used is to have two seperate grounds.

Set the amplifier circuit ground to 0V, and set your microcontroller ground to 2.4V.

To do that, you would use a 2.4V regulator for microcontroller ground, and a 5V+2.4V regulator for the positive voltage of your microcontroller.

Then just design your amplifier gain to not go above the 5V+2.4V voltage.

Ok maybe not elegant, but it works really well!