Really need some help.

[stickpin]

Ok, i need to design an opamp that uses just single rail supply. I know it can be done with the CA3140? and i have some to hand. However i cant seem to get any gain with this! am i doing something wrong? i have tryed inverting and non-inverting configeration just like i would with say an LM741 dual rail opamp.

Maybe someone can post some diagram up ?

thanks

 

[gramo]

Im a big fan of the MC34072

Its a single supply, rail to rail opamp


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More can be found at the bottom of this **broken link removed**

 

[audioguru]

Hi Grammo,
The MC34072 is not rail-to-rail.
Its input common-mode voltage range is 0V to 1.8V less than the positive supply. Its output low voltage is 0.3V above the negative supply and its output high voltage is 0.7V less than the positive supply.

 

[gramo]

Hi Grammo,
The MC34072 is not rail-to-rail.
Its input common-mode voltage range is 0V to 1.8V less than the positive supply. Its output low voltage is 0.3V above the negative supply and its output high voltage is 0.7V less than the positive supply.

Sigh, sorry about that

Its a single supply 3V to 44V opamp though, and I use it primarily with some applications because of its decent source/sink current capabilities (30mA)

You can take the high end right up to 5V if you power it with 6V+, but you will never get right on 0V on the bottom end

audioguru, you recommend a newish decent single supply rail to rail opamp for simple applications?

 

[audioguru]

I have never seen and have never needed a rail-to-rail opamp. Most are Cmos with low max allowed supply voltage.
I have used the MC34071 single, MC34072 dual and MC34074 quad opamps for projects and also the similar MC33171, MC33172 and MC33174 low power opamps.

 

[Hero999]

It depends on what you want, the LM358 is slow but will do for many applications.