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 http://sci-toys.com/scitoys/scitoys/light/light.html


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.

Tia
Sal2

On 1/7/08 9:00 AM, in article
, "sal2"
wrote:

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 http://sci-toys.com/scitoys/scitoys/light/light.html


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.

Tia
Sal2

You need the transformer to transform the current in the 8 Ohm side, to a
higher voltage on the 1000 Ohm side.

R.S. Has a 8:1000 Ohm transformer for a few dollars.

On Mon, 07 Jan 2008 17:00:37 GMT, sal2 wrote:

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 http://sci-toys.com/scitoys/scitoys/light/light.html


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.

Tia
Sal2

http://www.eio.com/repairfaq/sam/laserdps.htm#dpsicd

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
source.
--

default wrote in
:

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

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.

http://tinyurl.com/32wmcs

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.