I'll need to design a driver for my laser diode with feed back, I have found this circuit but I dont know how to analyse it:
In the circuit Q1 and the emitter resistor R2 form a constant current circuit, whose current level is set the voltage applied from U1 via R1.
The Vref sets the Vs output of the OPA. When the Laser is energised the D2 diode detects the emitted light. The strength of the light detected is amplified by U1, as the strength of the emitted light detected rises, the output of U1 falls so that constant current is reduced to ensure the laser current stays within it current limits.
A quick test would be insert a 50mA current meter in place of the laser diode.
Adjust the Vref pot so that the meter current is about 20mA.
Of course without optical feedback the output of U1 will be constant.
When you reconnect the laser diode any current due to the laser light falling on the D2 diode will drive the U1 output in a direction that will reduce the current below 20mA.
Does this help?