Negative Feedback Circuit Design

[hinisli]

Hi everyone. I am a senior student at university. We have a graduation project. We have to design a laser driver circuit with negative feedback. I searched internet but could not find anything. So, I am asking for your help. The purpose of our project is stabilizing the output of the laser. We have a set output value. If the output value is higher than the set value, the voltage that feeds the laser will decrease and if the output value is smaller than the set value, the voltage that feeds the laser will increase. These ways, we want to stabilize the output. We designed a Photodiode Amplifier (Since the output value is so small, like uA or nA we have to increase this value and convert it to the voltage), we have some different ideas about choosing the laser and driver but the main problem is designing the negative feedback circuit. If you can give some ideas about how we can do this design, it will be great.

 

[jiripolivka]

Some lasers come with a built-in PIN diode that should be used in the negative-feedback circuit to keep laser current constant over temperature.
Laser driver should be designed to keep the current within limits, and feedback from the PIN photodiode and temperature sensor is used to keep light output stable.

 

[erikl]

If you can give some ideas about how we can do this design, it will be great.

Here's a relatively simple laser diode driver circuit with photo diode control:

 

[crutschow]

The feedback is used to regulate the laser current, not its voltage.

 

[hinisli]

The thing is we have allready built a very nice amplifier circuit but we are having trouble to build the circuit especially when the voltage is more than the set value