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OPA690: Driver for a laser diode on OPA690

Emil Agayev
Prodigy 40 points

Part Number: OPA690
Other Parts Discussed in Thread: OPA357, , LMH13000

Tool/software:

Hello team. I have built a driver for a laser diode on OPA690. The control signal is a sine wave 40 kHz, 1.8 V. The thing is that at the output there is only a sine signal, but the laser does not light up. But without the transistor, everything works fine. At the output of the second microcircuit, I get a clean sine wave signal without distortion and 190 mA. What error do you see? The thing is that when I change the microcircuit to OPA357 and transfer the second cascade to a single-polar power supply, everything works fine. But I need the whole circuit to work from a bipolar power supply. Please help me figure this out.

  • 0
    TI__Mastermind 32395 points

    Hello Emil,

      A couple questions based on your findings:

    1. Does the laser light up when you only remove the transistor, Q1, and everything else in shown schematic is the same?
    2. With transistor, but change first stage to OPA357 and second stage to single-supply, laser lights up?
      1. In schematic, second stage is already single-supply of -5V, does this need to be dual-supply?

    Thank you,

    Sima

  • 0 in reply to Sima Jalaleddine
    Prodigy 40 points

    Hello Sima Jalaleddin. The answer to the first question is yes, the laser lights up without a transistor.
    The answer to the second question is I don't know, I haven't checked.
    The third question is, I need the same power supply as in the circuit. +-5v ground. This is the bipolar power supply in my circuit. Thanks for the answer.

  • 0 in reply to Emil Agayev
    TI__Expert 5386 points

    Please look at the integrated laser driver LMH13000 , it can enable you to modulate the laser using VSET pin .