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Dear all..
I would like to use this circuit (please see photo) for driver a laser diode to  engraving wood
-Item Name:ML101U29-25 (Mitsubishi)

Power output: CW 300mW

Pulse Power: 400mW

Working Current: <340mA

Working Voltage:2.2-3.0V

I know about this formula I = V/R But in this circuit I am not sure for calculate current .So please could you help me to know how many (mil.amp) I must setting for 9 volts power with maximum output 300mW (with safe laser diode ).
-Or you show me other best circuit
Many thank you.

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1. it is a dirt cheap driver.
2. I hope you are not talking about a 9V battery here.
3. You will need a proper multimeter to set the circuit right - there is no other way.

Hi Downunder35n

you said :* not talking about a 9V battery here*

for me easy understand Thank you so much

You laser uses quite a bit of power and a 9V block battery is about the weakest energy source you can find for that voltage.
AA batteries are quite small, AAA even smaller - in your 9V battery are 6 1.5V batteries that are smaller than a AAA.
Since you need less voltage anyway either use 3 D-cells or a wall adapter - those for mobile phones, providing 5V and 2A would work fine too.

I made a diode driver awhile back and I found that using 4 D cells made it the brightest but still didn't pop a balloon (I was using a RW dvd laser!) just something I found

Hi bravoechonovember1

With my little experienced You need 2 things for do pop a balloon :

- power laser from 50mw or more

- focus lens must be right in place more power more easy adjust the lens .

Thank you

Dear steveastrouk and iceng

Many thank you for your time help me.

The circuit lets you adjust the current from a high of 240ma to a low of 12ma.

The only consideration for the battery is if it is capable of sourcing the desired current and exceeds the laser forward voltage plus three volts.

I am curious if the laser diode will lase over that range that simple constant current circuit will do. Also that pot may be too small.

sure won't carry 240ma. There are ways round the issue though