op-amp circuit wont work

Jul 21, 2011 35 Replies

can anyone tell what I did wrong here? my goal is to measure current using an opamp, I need to be able to measure positive and negative current, and I have these LTC2053 OpAmps available, but I'm trying to simulate what I'm thinking about doing in LTspice and I can't get any output at all.... I need to be able to see from 50uA to .1mA, which is a pretty big range (and I need this in positive and negative directions) here's a link to the circuit I made in LTspice, much thanks


LTspice:

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LTC2053 datasheet:

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Post your LTspice schematic, *.asc is text and you can it post here.

Looks like it should be working, but a look at the LTspice file will tell us a lot.

Or you can ask Larkin and he'll tell you how wonderful he is and he will go on and on for days... and you will know less than you do today :-) ...Jim Thompson

[On the Road, in New York]
| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.

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So, you can't simulate without the OP posting the text file? You are less helpful than I suspected.

Of course. You just had to get that off-topic dig in didn't you? You have become repulsive in my opinion for your inability to control yourself. Shame on you.

Define "can't get any output at all". Seems to me that you should have 150mV (one way or the other) at the output. Posting the netlist is the best way to get help. Most of us can stick it in LTSpice to look at the schematic.

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Try this:

In LTSpice, open a new schematic.

Place an LTC2053.

Right click on it and then click "open this macromodel's test fixture".

Then modify accordingly.

Hope this helps.

..

150mV

way to

Basically I get a steady -0.5mV at the output, if I make my load resistance smaller, this value goes to zero.

thanks

"ExpressPCB Netlist" "SwCAD III Version 4.11z"

1 0 0 "" "" "" "Part IDs Table" "V1" "5" "" "U1" "LTC2053" "" "R1" "1K" "" "R2" "2K" "" "R3" "1" "" "R4" "100k" "" "V2" "-5" "" "I1" ".05" ""

"Net Names Table" "N001" 1 "0" 3 "Vin" 12 "N002" 15 "N003" 17 "Vout" 20

"Net Connections Table"

1 1 1 2 1 2 8 0 2 1 2 4 2 2 1 5 2 2 2 6 2 2 5 7 2 3 2 8 2 5 2 9 2 6 2 10 2 7 2 11 2 8 1 0 3 2 3 13 3 5 1 14 3 8 2 0 4 2 4 16 4 7 1 0 5 2 6 18 5 3 1 19 5 4 1 0 6 2 7 21 6 4 2 22 6 6 1 0

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He's bragging that he has kill-filed me, and he's obviously obsessed by me, and pretty much dedicates all his posts to me. Figure that out.

John

t

...

ve 150mV

t way to

c.

thank you, I opened up the test fixture like you suggested and noticed that the enable pin was wired to the negative rail.... I had mine wired to ground, thinking that since it's an active low input this would do it.... I've since hooked mine up to my negative power supply and it's working now.

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a

on

Your reply was not necessary, John.

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us a

on

This is a newsgroup. None of it is necessary!

John

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us a

go on

Do you really think that makes your point?

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So, you can't simulate without the OP posting the text file? You are less helpful than I suspected.

Of course. You just had to get that off-topic dig in didn't you? You have become repulsive in my opinion for your inability to control yourself. Shame on you.

--------

and yet you respond to a response that is OT with an OT response.... You should think twice about voting for Obonkers again.

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us a

go on

My point is that there is no point!

John

I have a follow up question about this circuit, I'm really interested in being able to measure 50uV at the input, by adding gain and seeing something at the output.... I was thinking with a gain of 21, this would get me 1.05mV at the output and I could work with that. But, when I apply zero volts at the input I get 20mV at my output. In the datasheet it says the offset voltage is below 10uV... why am I seeing this 20mV? I tried just connecting both input pins to ground and still get 20mV at the output.... also, is there any particular range of resistors that I should use in my feedback? I mean, if I want a gain of 21, I need a ratio of 20 from R2/R1.... does it matter if I use 20k/1k or 200k/10k or 2k/100?

much thanks

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Sure, I can do that but then I don't see any hidden modification he might have made. It's easier for him to post the netlist than it is to link a picture.

You're the only one who still trollbaits him.

Hope This Helps! Rich

Look at the structure of this sequence. I did not respond to his posts. He did, admittedly lamely, attack me by name in response to a purely technical post by someone else. My response was to John S.

Crazy old geezer. Has nothing to say about electronics any more. Must have run out of broken lampshades to repair.

But since he's killfiled me, you can't accuse me of baiting the batty old hen. He can't see my posts.

John

will

)

You seem to be on the defense. Must be nice to be killfilled by someone from MIT? Wish I could brag about that.

-Bill

enig4171597386F8F359E25336BF Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

John Lark>> Do you really think that makes your point?

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mike

Defense? From what?

Must be nice to be killfilled by

I wish he'd actually do it. What sort of idiot would keep telling me that he has killfiled me?

John

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