# How to change the voltage polarity in an inverting amplifier?

I want to implement a simple circuit which can map -10V +10V voltage range to 0V 5V voltage range. Thus I'm planning to use two op-Amps, one for the slope and the other for the offset. So basically I'm planning to use an inverting amplifier and a summing amplifier consecutively.

But Inverting amplifiers multiplies the input voltage with a minus sign. I need a positive slope. How can I overcome this? Also Could you gibe me any ideas for a cheap op-Amp models for this purpose?

• Don't use an inverting amplifier OR if you do use two with the 2nd one restoring the slope. – Andy aka Aug 24 '13 at 14:03

## 1 Answer

There is a calculator on this website here. Here are the results for the two scenarios of: -

• input voltage = -10V, o/p = 0V
• input voltage = +10V, o/p = +5V I've arbitrarily chosen R1 to be 1K and I knew from experience that V2 needs to be half the range of the output requirements so I set that to 2.5V. By simple examination of range of input voltages to range of output, the gain has to be 0.25.

As you can see, both scenarios produce the same result of R2 = 250ohms, R3 = 1kohm and R4 = 250ohms.