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Design >> Analog Design >> problem with current to voltage converter
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Message started by neuro11 on Dec 10^th, 2014, 11:40pm

Title: problem with current to voltage converter
Post by neuro11 on Dec 10^th, 2014, 11:40pm

I am trying to test the attached circuit (changed R2 to 1 k) by supplying current (1.5 mA) using the CC mode of a DC supply. But i can not identify any change in ouput voltage with the change in feedback resistance (200 ohm - 1 kohm). I am using 12 volt single power supply. and the output i am recieveing around 1.3 volt. i attached a multimeter in series with input and the current remained almost constant with the change of resitors. can anyone tell me what is excatly wrong here. I tried using 3 different ICs lm358,lm393 and ltc1052. but i could not amplify the signal with either of them.

Title: Re: problem with current to voltage converter
Post by loose-electron on Dec 11^th, 2014, 11:31am

you are slammed against the ground

suggest looking at some web sites or books - google "basic op amp circuits" or similar.

Title: Re: problem with current to voltage converter
Post by loose-electron on Dec 11^th, 2014, 11:34am

Oh, and your 15v supply in the picture has not been established relative to your ground so there is no telling where all your power supplies and ground are relative to each other.

Title: Re: problem with current to voltage converter
Post by neuro11 on Dec 14^th, 2014, 7:15pm

The power supply picture was wrong at drawing. But in reality , the supply was between 12 V plus and ground. So there should not be a problem with this.
Regarding the circuit i checked in basic circuits and the current to voltage converter are exactly same. what i am doing with the ground is connecting all the negative points together (power,non inverting terminal, negative connection of input) and out is measured against the same ground. dont understand whats doing wrong with ground though. can you plz be specific about the fault

Title: Re: problem with current to voltage converter
Post by raja.cedt on Dec 15^th, 2014, 2:36am

Hello,
In your schematic connection are very confusing, vs+ in the top connected to -ve supply of the opamp, is ground connected to vs-? Any how take care of the supply.
When you have some opamp based circuits, just before applying any input/signal just check inverting and non-inverting terminals, they should stay at expected and defined potential. In the current case both inputs and output should be at ground, if this is okay then apply current and check the o/p change.

Thanks,
Raj.

Title: Re: problem with current to voltage converter
Post by loose-electron on Dec 17^th, 2014, 5:40pm

please provide an accurate schematic of what you have and what you are observing

if you can't do that you won't get useful help :(

Title: Re: problem with current to voltage converter
Post by Novaris on Dec 21^st, 2014, 12:36pm

Its basically never a good idea to connect together vss or v- and the agnd or in your case the in+. Just imagine: if you drive current into the circuit the output must go below the voltage at the input node which, ideally, is the voltage of the reference, so agnd. If agnd is v- the output can't go below that and clips. Also, most opamps dont perform well when their inputs are near the supplies.

BR