Can a single single supply op amp be used as a summing circuit?

What a coincidence: there's a thread in s.e.b. that discusses this at length.

John

If you read the thread, you would also know that I was unable to get an answer.

On Oct 8, 12:41=A0am, Andy wrote:

Seems odd. This seems to work in LTSpice. The 1.25V voltage reference could be any one of number of three-terminal references, such as the

You might need to buffer your source.

Version 4 SHEET 1 980 680 WIRE 0 -304 -176 -304 WIRE 816 -304 0 -304 WIRE 976 -240 704 -240 WIRE 704 -192 704 -240 WIRE 0 -160 0 -304 WIRE 512 -112 96 -112 WIRE 512 -96 512 -112 WIRE 816 -48 816 -304 WIRE 704 -32 704 -112 WIRE 784 -32 704 -32 WIRE 976 -16 976 -240 WIRE 976 -16 848 -16 WIRE 512 0 512 -16 WIRE 784 0 512 0 WIRE 512 32 512 0 WIRE 704 128 704 -32 WIRE -176 144 -176 -304 WIRE 96 144 96 -112 WIRE 512 144 512 112 WIRE -176 352 -176 224 WIRE 0 352 0 -96 WIRE 0 352 -176 352 WIRE 96 352 96 224 WIRE 96 352 0 352 WIRE 512 352 512 224 WIRE 512 352 96 352 WIRE 704 352 704 208 WIRE 704 352 512 352 WIRE 816 352 816 16 WIRE 816 352 704 352 WIRE -176 400 -176 352 FLAG -176 400 0 SYMBOL voltage -176 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V1 SYMATTR Value 10 SYMATTR SpiceLine Rser=3D0.1 SYMBOL voltage 512 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V2 SYMATTR Value 1.25 SYMATTR SpiceLine Rser=3D0.1 SYMBOL voltage 96 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V3 SYMATTR Value PULSE(0 5 1u 1m 1m 1m 5m 1) SYMATTR SpiceLine Rser=3D0.1 SYMBOL Opamps\\\\LT1006 816 -80 R0 SYMATTR InstName U1 SYMBOL res 528 128 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R1 SYMATTR Value 47k SYMBOL res 528 0 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R2 SYMATTR Value 47k SYMBOL res 688 112 R0 SYMATTR InstName R3 SYMATTR Value 30k SYMBOL res 688 -208 R0 SYMATTR InstName R4 SYMATTR Value 18k SYMBOL cap -16 -160 R0 SYMATTR InstName C1 SYMATTR Value 100n TEXT 168 408 Left 0 !.tran 0 5m 1u 100n startup

-- Bill Sloman, Nijmegen

It takes two resistors. That's stated a couple of times over there.

John

What is your point in replying? Why take the time to post at all if you have nothing to add? I post questions because I am looking for answers. Perhaps you can explain how a voltage divider circuit can create a voltage offset, as opposed to simply a voltage scaling.

It was explained in s.e.b. in words. OK, here it is in pictures:

Add single-supply opamp input and/or output followers as your application may need them. Scale the resistors if that suits.

John

"Andy the Witless"

Perhaps you can explain how a voltage divider circuit can create a voltage offset, as opposed to simply a voltage scaling.

The assumption is being made that your 0-5V source can sink current too.

.... Phil

What? Was the solution too simple for you? Or is there some reason it won't work?

George H.

It was explained in pictures too.

The part he didn't get was that the output was referred to ground, not to the input voltage:

GND>-----------------------------gnd

The gmail (non)intellectual level ;-) ...Jim Thompson

--- I agree, plus some of the arrogant spoiled brat google groupers think that the world owes them a living.

Case in point, what's-his-face posted, when he ran out of rope:

"What is your point in replying? Why take the time to post at all if you have nothing to add? I post questions because I am looking for answers. Perhaps you can explain how a voltage divider circuit can create a voltage offset, as opposed to simply a voltage scaling."

It's as if, he thinks, even though it's all been explained to him, time and time again and he doesn't understand it, it's his teachers' fault that he's stupid.

I think he needs to look at his lineage...

What? An Obama relative ?:-) ...Jim Thompson

ual

Really? Would you like to identify the flaw in the circuit that makes me unemployable?

-- Bill Sloman, Nijmegen

Bwahahahahahahaha! You finally sucked Slowman in with enough rope that he not only hanged himself but pulled out his tongue as well ;-) ...Jim Thompson

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The OP wanted a 1V offset. This requires some kind of reference voltage - V2 in my circuit.

You can use a power supply rail as a reference voltage; power rails are rarely tightly specified, and they tend to be noisy. Your customers are obviously pretty undemanding - they wouldn't be your customers otherwise - but the people I've worked for have been into joined-up words and stable offsets.

Where were you going to get your offset?

-- Bill Sloman, Nijmegen