Laser diode driver

Laser diode driver

Here’s a quick project I made in couple days or so. It is a push-pull step-down laser diode driver based on LT1683 SMPS controller chip from Linear Technology. The circuit works with 12-18V input and can put out about 1A to a 2V load. I used a PL140-105L planar ferrite transformer from Coilcraft which is quite overkill for this application (it is rated for 140W).

LT1683 laser diode driver schematic

LT1683 laser diode driver schematic

The circuit has a current clamping circuit (so you can limit the maximum current based on your laser diode), a self-enable circuit (which enables the driver after the +5V rail has stabilized) and an open-laser protection feature which limits the open-circuit voltage. The circuit is based on an application note from Linear.

I didn’t implement the open-laser feature because I accidentally used an SO8 footprint for the LTC1696 chip. It would have require some IC-yoga to get the SOT23-6 chip to fit there so I didn’t bother with it.

There is at least one gotcha with the driver, you need to use the enable signal (or the self-enable circuit) or you WILL get severe current overshoot on start-up because the error amplifier is saturated:

Laser diode driver set to 300mA, 2V load, without self-enable

Laser diode driver set to 300mA, 2V load, without self-enable

If you use the self-enable circuit or use some other method of enabling the circuit, it works great without any overshoot.

I was in a hurry so I got a some bugs on the PCB design, like having the + and – inputs on the LT1013 error amplifier the wrong way around, doh!

5 Responses so far.

  1. Angel G. says:

    It’s good, but only if you ‘re using the LASER as a torch or lamp. If you need to modulate it – for example to draw something, it won’t work.

  2. Benjamin Mellibovsky says:

    Dear Kalle
    Thank so much for the information Fantastic!!
    I need to made for me a laser diode driver for a max of 20W
    Do you have more information to can send me like a PCB board drawings to can make one
    Thank you in advance for your consideration


    • Hello Benjamin! Unfortunately I’ve lost the design files when my harddrive failed.

      • Benjamin Mellibovsky says:

        Bad Luck 🙁
        Did you tested the driver some time
        Can be works with a 10w 808nM laser diode?
        The diode wark with 2.2v at 10Amps

        Best Regards

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