Flipping a voltage signal

Hi all,

Well, this is either going to be easy or impossible. I have a signal from a current transducer that produces a 0 to 5 VDC signal - 0 V when no AC current is detected, up to 5 V when it detects full scale AC amps. I want to use that voltage signal as an input to a motor controller, but I would like it changed from 5 to 0 VDC. That is, I want the full 5 V signal present when the transducer measures zero current, and zero volts present when the transducer has the maximum current through it.

Is there a simple circuit to do this? The controller has a +5 V pin, a signal pin, and ground for its voltage command input.

Thanks in advance.

Use an inverting op amp with a gain of one, and an offset of +2.5V applied to the plus(+) input (See below).

If your supply is +5V you will need a rail-to-rail type op amp.

Hi Carl,

Yes, this will do the job, thanks. Two last questions - I have the resistors, but would you suggest a particular type/vendor for the op amp? Is the 2.5 V offset done with a battery? Thanks again.

jcganley said:

Yes, this will do the job, thanks. Two last questions - I have the resistors, but would you suggest a particular type/vendor for the op amp? Is the 2.5 V offset done with a battery? Thanks again.

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A rail-to-rail op amp such as the TI TLV2374 should work for you application with a single 5V supply (you didn't state what your supply is).

The 2.5V can generated by a resistive divider from the power supply. Two equal resistors from a +5V supply will give 2.5V.

Thanks a million - I'll look for the TI.