Designing a 0-20uA High Precision Voltage to Current Converter Circuit

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How can I build a voltage-to-current converter that produces 0–20 µA for testing a photodiode-based position-control feedback circuit?

Use an op-amp based voltage-controlled current sink to replace the photodiode outputs; Steve provided a custom circuit for this and said it can be simulated [#21667442] He confirmed the circuit will give 0–20 µA with about ±20 nA variation [#21667444] For the op-amp, he suggested the MC33172, which provides two op-amps for your two current sources [#21667444] He also assumed a 0–2 V input range and noted that the required resistor R1 is set from the input-voltage range; the MC33172’s 2.0 mV input offset is usually not a problem, though it may matter near 20 nA [#21667444]

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#1 21667436 07 Apr 2013 07:19

ganesh Bhosle ganesh Bhosle

Anonymous

Post #1
21667436 07 Apr 2013 07:19

Hello,
I want to design Voltage to current converter for testing of my application. Required current needs to be vary from 0-20uA. Can anybody please help me..

Thanking you

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#2 21667437 07 Apr 2013 07:26

Frank Bushnell Frank Bushnell

Anonymous

Post #2
21667437 07 Apr 2013 07:26

If you can explain your application and provide a circuit diagram, it will help us to understand your requirements.
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#3 21667438 07 Apr 2013 08:03

ganesh Bhosle ganesh Bhosle

Anonymous

Post #3
21667438 07 Apr 2013 08:03

basically I have two current to voltage converters and difference of these output used for feedback.

these two I to V converters are interfaced to photodiodes. I have to replace those sensors by V to I converters for Testing purpose.
it is used for Position control. please can you give any kick start.
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#4 21667439 07 Apr 2013 08:47

Steve Lawson Steve Lawson

Anonymous

Post #4
21667439 07 Apr 2013 08:47

Perhaps something like this will do the trick:

* http://basicelectronic.blogspot.com/2006/08/constant-current-source-circuit.html
* https://www.circuitlab.com/circuit/63wt5z/constant-current-source-led-driver-linear-01/
#5 21667440 07 Apr 2013 08:50

Steve Lawson Steve Lawson

Anonymous

Post #5
21667440 07 Apr 2013 08:50

BTW: instead of a voltage reference on the inverting input (of the op-amp), apply your input voltage (i.e. the inverting input becomes your input voltage -- for a voltage-to-current conversion).
#6 21667441 07 Apr 2013 08:59

Steve Lawson Steve Lawson

Anonymous

Post #6
21667441 07 Apr 2013 08:59

Also, I just realized the above are current sources and perhaps you require a current sink:

* http://en.wikipedia.org/wiki/File:Op-amp_current_source_with_pass_transistor.svg
* http://en.wikipedia.org/wiki/Current_source

In this case the non-inverting input becomes the control voltage.
#7 21667442 07 Apr 2013 09:29

Steve Lawson Steve Lawson

Anonymous

Post #7
21667442 07 Apr 2013 09:29

OK,

None of the references I supplied is quite right, so I did my own:

* https://www.circuitlab.com/circuit/56kcwf/voltage-controled-current-sink/

Follow the link and read the Summary for details about this circuit. You can also "Open in Editor" and simulate it and otherwise play with it
#8 21667443 10 Apr 2013 05:43

ganesh Bhosle ganesh Bhosle

Anonymous

Post #8
21667443 10 Apr 2013 05:43

Thank you for guidance. still I have few queries.
1. will this configuration give me 0-20uA current variation ( as a replacement to photodiode). or
2. What parameters shuld I look for selecting the components like op-amp?
3. Do I need any offset composentation?
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MC33172 suggested for dual current sources
#9 21667444 13 Apr 2013 10:50

Steve Lawson Steve Lawson

Anonymous

MC33172 suggested for dual current sources
Post #9 21667444 13 Apr 2013 10:50

1. Yup: 0-20uA (±20 nA)
2. The mc33172 is probably a good choice -- two op-amps for your two current sources.
3. The mc33172 has an input offset voltage of 2.0mV, so you probably won't notice (or maybe you will when you get down to the 20nA range -- if that's a problem then let me [us] know).

BTW: you never divulged the voltage range for your "Voltage-to-Current" conversion. I assumed 0-2 volts. But, if you need different, I supplied a formula for determining R1 in terms of the input voltage in the above link (it was down for a short while, so try it again, if it previously failed).
#10 21667445 16 Apr 2013 04:43

ganesh Bhosle ganesh Bhosle

Anonymous

Post #10
21667445 16 Apr 2013 04:43

thank you Mr. Steve for your guidance. I will work out with suggested chip and let you know the results.
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Topic summary

The discussion focuses on designing a high precision voltage-to-current converter circuit with an output current range of 0-20µA, intended to replace photodiode sensors in a position control application. The user requires a voltage-controlled current sink or source to simulate photodiode outputs for testing purposes. Suggested solutions include constant current source circuits and voltage-controlled current sink designs using operational amplifiers. Key advice highlights using the MC33172 dual op-amp for implementing two current sources, with attention to input offset voltage (approximately 2.0mV) and component selection based on the input voltage range (assumed 0-2V). Reference circuits and simulation tools were provided to aid design and verification. Offset compensation may be necessary if operating near the 20nA resolution level.
AI summary based on the discussion. May contain errors.

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Designing a 0-20uA High Precision Voltage to Current Converter Circuit

Designing a 0-20uA High Precision Voltage to Current Converter Circuit

How can I build a voltage-to-current converter that produces 0–20 µA for testing a photodiode-based position-control feedback circuit?

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