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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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## 9 Replies

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.

lam (author)2015-10-31

Hi Downunder35n

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

for me easy understand Thank you so much

Downunder35m (author)2015-11-01

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.

bravoechonovember1 (author)2015-11-03

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

lam (author)2015-11-03

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

lam (author)2015-11-01

Dear steveastrouk and iceng

Many thank you for your time help me.

iceng (author)2015-10-31

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.

steveastrouk (author)2015-11-01

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

steveastrouk (author)2015-10-31

I=1.22/R ?