current-voltage converters and vice-versa

[Tori]

Hi,

I was wondering if anyone could advise me on a project that I have just been given. Any advice such as where to begin and what circuits might be useful would be very helpful.

The project is to design 2 converters:
1. voltage - current: Input= 0-1V, 1mA max; Output= 4-20mA
2. current - voltage: Input= 5-20mA; Output= 0-5V

The aim of the project is to investigate opamp circuits, so any information that you could give regarding these circuits (involving opamps) would be appreciated.

Thank-you

 

[plot]

For constant current, you simply tie the + side of the opamp to ground, and have a feedback resistor going in the - side, and a set applied voltage going through a resistor into the - side.

So, have a 1 volt supply going through a 1kOhm resistor, this will create 1 mA. send that into the - side of the OpAmp (current doesn't actually go into the - side, that 1mA will actually flow through the feedback resistor). You'll need to calculate the value of the feedback resistor to get the desired output current you want.... My suggestion: creat this circuit in a Spice simulator such as Orcad PSpice, Electronics Workbench, or my personal favorite, Switchercad III (available for free from www.linear.com), and plug in some numbers for that feedback resistor until you see the output you want.

 

[red4925]

voltage - current converter: look up transconductance amplifier in any electronics text or on the web
current - voltage converter: look up transimpedance or transresistance (outdated term)

These op-amp configurations are pretty simple and should be easy to understand from any text or decent web page.