Hello,

I was wondering about the best op-amp to use for a photo-diode in trans-impedance amplifier configuration. Is the trusty LM741 op amp good enough? I've been searching Google and i havn't had an answer in layman's terms that i can understand. At the moment i have an photo-diode amplifier , a LTC1050 set up in the configuration in the picture

And the circuit is working fine, would i be right in saying this is in photo-voltaic mode rather than photo-conductive mode?

Also the amplifier i have used has only a +5V supply, how can this work as i thought all op-amps need a split power supply +-5V.

 

If you are using it as an opto switch, comparators are much, much faster than an op-amp.

LM741's are archaic. A 741 is an internally compensated 709, the grandfather of all op amps. There are numerous parts with much better specs such as the TL072/TL082 series for general use.

 

The amplifier selection depends on the circuit application, and you have not defined the application with specifications. Give us more data.

 

Hello,
Well Currently i am using a LTC1050 op amp (single supply +5v) and using a BPW24R (generic photoDiode i found on RS components) Attached is the circuit i am running currently, and it works (probing the output with an oscilloscope), i just want to know why the op amp only requires a single supply and whether this is in photovoltaic mode? I am confused as to why this circuit works when i thought that op amps require split supply like +-5V. I am currently experimenting with trying it in a photoconductive mode (circuit, see attached) using the same op-amp with a split dual supply (two 9v Batteries) but having no luck , is there something fundemental i am missing here?

 

I want to use the photo diode for position sensing, i.e. when the LED shines on the photo diode the Arduino knows that an object is not near enough, when the LED light source is fully covered the arduino knows that the object is too near and when the LED light source is half covered the object is at the right position. See picture.

 

The be LTC1050 has a maximum voltage rating of 18V when may be slightly exceeded by your two 9V batteries. Otherwise don't know why your photoconductive mode circuit doesn't work. If the photovoltaic mode works why do you want it to work in the photoconductive mode?

The single-supply circuit is working with zero bias on the diode. I believe that's considered a photovoltaic mode. That circuit needs no negative supply since the op amp is designed for single-supply operation and you don't need a negative output.

The LTC1050 op amp is a zero-drift type so the output DC level will stay very stable with time and temperature changes. A 741 is an ancient, noisy, poor performing device and I won't used it for anything.

 

Ahh ok , as im just playing with op amps and photo diodes for the first time i wanted to see what circuits i could build, and what the difference would be , i've heard that biasing the photo diode will give a linear response to light intensity and a faster reaction times ( for my hobbyist project most likely unneeded) while being more noisy. Im going to try and use a power pack with split supply and lower it to +-5V and supply the op amp tommorow to see if i can get the photoconductive circuit working. Thanks for the help!

 

In the photoconductive mode you don't need the 800k resistor to ground.