OPamp based laser driver circuit

[frankqt]

Hi I like to design a laser driver that can regulate the current based on the photodiode inside its package. Basically a constant output laser diode. I also need to modulate the output of the laser at 1MHz using pulses. Any pointers or reference schematics I can use?

 

[keith1200rs]

Look at the chips make by ic-haus, they are designed for the job. Opamps are not ideal as they are unpredictable on switch-on, but can be used with careful design.

Keith

 

[frankqt]

Keith,

My circuit is not very fast, up to about 1MHz. I have several of these lasers which they are all synchronized. Having 6 of these chips are not very cost efficient. Assuming IC hous is a small semi company, I suspect this would be an expensive approach.

What I am looking at is a way to use the feedback from the PD of LD to tune the LD current so that the light output is optimal. Most of the circuits out there are based on transistors but I am not confident on that approach.

 

[keith1200rs]

The Transistor based circuits are probably a safer approach than trying to use opamps! Many years ago I was asked to design a laser driver for a company whose lasers were often blowing up during testing. They had an opamp circuit which did unpredictable things for a few microseconds at switch on. That was all that was needed to overdrive the lasers and blow them up. I designed a simple 2 transistor circuit for them which they then patented - it worked perfectly.

You can get round the opamp problem by adding a transistor(s) on the output and including a long time constant so the opamp is ignored at switch-on.

If you post the circuit you would like to use we can comment on its suitability.

Keith