Laser driver

[Martt]

Hello im trying to build laser driver and got some questions. I made a scheme, i hope you understund it. Anyway what makes me a question is power supply, potentiometer, fan.
1) 9v and 2 amps supply should be the best? How do i can calculate it?
2) Potentiometer. I want to use it, in this case how do i know which would be the best? 100 ohm should be the best?
3) Lets say i wanna add one fan too which is 9 v and 0,1-0,2 amps. i could also use 12v one but i cant find its amps. How to add fan ? And everything changes ? I mean what about power supply etc. then?

Thanks.

 

[Martt]

Sorry i found one mistake. I forgot diode to connect minus side

 

[(*steve*)]

watch out. If you set the potentiometer to near zero you'll probably let the smoke out of it

 

[Martt]

watch out. If you set the potentiometer to near zero you'll probably let the smoke out of it

How? 1 ohm is enough... according to ohms law...

 

[(*steve*)]

you may dissipate more power in a portion of the resistance track than it is rated for.

lets say your pot is rated for 10W but current is passing through only 20% of the resistance track (e.g. 100 ohm pot set to 20 ohms). In this case, that portion of the track can only dissipate 1W.

If this were the case in your circuit (100Ω 10W pot) set to 1Ω to have a current of 625mA, that part of the track (with 1% of the 10W rating) will need to dissipate 390mW, almost 4 times what it is rated for.

This can cause it to burn out.