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OPA569 laser driver

Mikhael MYARA
Prodigy 60 points
Other Parts Discussed in Thread: OPA569, TINA-TI

I try to build a laser driver. I found various designs, including op-amp current source followed by bipolar transistor. A specific design, based on OPA569, was more interesting to me as it features current limit. The exact circuit I'm interested in is available here :

http://www.youspice.com/ys/en/project/2-ampere-cathode-grounded-laser-diode-driver.3sp

I tried to perform numerical simulations of the ON/OFF transients by means of both TINA-TI v.9 (free version) and cadence-spice V. 16.0. Unfortunately, whereas TINA-TI exhibit nice transient shapes, the cadence-spice simulation exhibits very slow startup time with a long delay (10 µs !) and slow slope, while it demonstrates negative spikes up to -2 amps (!!!) during some µs during the "Off" transient. Please notice that I had to increase the amount of steps to reach convergence with cadence-spice.

Which of both simulation is "the good one" ?

Best Regards,

   Mike

  • 0
    Prodigy 60 points

    I'm sorry but the simulation now exhibit the same results ... I made the same mistake but many times ... The result is that the negative spikes truly exist.

    However I do not understand how can such a design fit the laser diodes requirements, which do not like both reverse current and spikes ...

  • 0 in reply to Mikhael MYARA
    Prodigy 80 points

    Have you tried adding 10uF capacitors to the output on this circuit?  Most of the laser drivers we have been doing at laserpointerforums.com have several capacitors on the outputs to dampen startup spikes.

  • 0 in reply to Paul Breakfield
    Prodigy 60 points

    Thank you for your answer. I just tried to add 1 uF and 10 uF capacitors. With 1 uF capacitor, no spike but strong reverse current is possible (> 30 mA). With 10 uF capacitor, just small negative current (30nA, I think it should not damage a laser diode), no spiking but bandwidth reduced down to 100 kHz - whereas the interesting thing (to me) with this laser driver was MHz bandwidth AND high current.

    Thank you once more ! 

      MIke