Zener_Diode

Hey all.
I saw the thread "Dual or single supplies for opamps" - but there are no information about IN, so I need to ask u the question:

I have a ciruit as shown in the jpg image.
when known:
Vdc>0
V1<=Vdc
Vout>0

In the calculation I have -R1/R2*Vdc, but Vout always positive.
Can I conenct the amp to single power supply or I have connect it to the dual one.
please explane.

thanks ahead.

Attached Images

amp1.JPG (7.3 KB, 24 views)

Hero999

You need a bipolar supply for this circuit.

Whilst it's possible to use a virtual earth circuit and just one supply, all the signals comming into and out of the op-amp need to be referenced to the virtual earth.

You can make a virtual earth with another op-amp so you could use a dual op-amp like the TL082.

Linked below is thread which deals with virtual earths.
http://www.electro-tech-online.com/e...wo-7805-s.html

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crutschow

Since the circuit you show is a non-inverting amp with gain, you can use a single supply only if the op amp is capable of rail-to-rail input and output voltages. A standard op amp, such as a 741, will only operate to within a couple volts or so of the supply rails.

Hero999

So it is, I didn't notice that, so yes, you can use a single supply op-amp like the LM358.

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Zener_Diode

thanks.