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Laser diode module and audio amplifier tia sal2

Discussion in 'Beginner Electronics' started by sal2, Jan 7, 2008.

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  1. sal2

    sal2 Guest

    Laser diode module and audio amplifier tia sal2

    Greetings All

    I have a laser diode module with the datasheet of
    output <5mw
    wavelength 640-660nm
    that is powered by 3Vdc I've created a simple laser communicator
    following the instructions from
    this site

    This works great but I was wondering if I
    could power my laser module using just the output of a cheap audio
    amplifier (like from radio shack) and not use the transformer
    if so what calculations and changes to the circuit
    would I need to make to prevent destroying the laser.

  2. default

    default Guest

    Shows linear audio modulator for line level inputs.

    Using a transformer may work OK - but bear in mind, if the transformer
    is modulating the voltage supply from the battery it would be very
    easy to over drive it hard enough to burn out the diode.

    A safer audio technique is to just use a transistor or mosfet in one
    leg of the power supply to just modulate the power supply without
    adding more energy to the circuit - to that end he shows a linear
    single transistor amp intended to go in the minus leg of the LD power
  3. MOSFET, I think, and for an easier way to be safe use it as a shunt
    modulator, in parallel with the laser diode. Enhancement mode MOSFET's
    aren't very linear, they're mostly used for power switching, but if you use
    an op-amp adder on the gate you can use a DC offset voltage varied between
    0 and 5 VDC to find the most linear region, then adjust the op-amp gain.

    I made that circuit as a basic laser mod input corrector, so it should be
    adaptable to this exactly as designed. Feed the audio into the first input,
    using that first control pot to adjust the volume. Second input is the 0 to
    5 VDC offset control. The enhancement MOSFET should be chosen for having a
    fairly wide and linear operating region. I'll leave that to you, or someone
    else, though I think the IRF510 should do it well enough. What's nice about
    this circuit is that the controls are stable, none is upset by changing
    another, and the whole thing can be run on a single low volt DC supply,
    like a battery.
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