Laser Diode CW Driver

Thread Starter

Félix Del Prado Hurtado

Joined Sep 25, 2019
Hello Everybody!
I am interested in feeding a laser diode (LD) with 2.5V and 210 mA. I am using basically a Darlington configuration as shown in the schematics.
In order to prevent any damage to the LD I am using a RL.
I have used 3 Op-Amps of the same kind labeled as Op-Amp #A, #B and #C all of them new ones
The list of elements that I am using are:
  • (FG) Frequency Generator: HMF2550, f= 10Hz,V_offset =2.000 V & 0.005 Amplitude (Output impedance = 50 Ohm)
  • (LD) Laser Diode: LNC728PS01WW
  • (Tx) Transistor: PN2222A NPN
  • (Pot) Potentiometer: Potentiometer 5W and 25 Ohms
  • (Z) Zener Diode: 3V
  • (OA) Op-Amp: AD848JNZ (PIN1 & PIN8 are not grounded, ot connected between them, simply not connected.
  • (PS) Power Supply: from a PC
  • (RL) Load Resistance = 2.2 KOhm
The values of the Voltages obtained are listed in the next picture.


Can someone Help me, why there is not voltage drop through the RL? Why the PINs 1 & 8 show these values?

Thank you very much in advance.


Joined May 20, 2015
Will your T2 transistor be able to dissipate approximately 1.5 watts of power ((12-2.5-2)*0.21 = 1.575)? This question arises when connecting the laser.