The Requestdear swagatam, I'm emailing you to ask you for your expertise, and you
being one of India's finest electronics engineers I thought you be the
best man in the world to know, bear with me my friend its a bit of a
I brought some 10 milliwats laser diodes from xxxx electronics here, the data on them isn't much but maybe enough to go by, they are 2.4 volts and the threshold current is 24 milliamps and the
maximum current is 40 milliamps , now I've looked all over the net for a
power supply circuit using the lm317 regulator for this diode but there's circuits for other diodes only but there voltage and currents are
different so trying to find a simple lm317 regulator circuit that will
deliver 2.4 volts dc at up to or near 40 milliamps is hard .
used an lm317 regulator calculator for voltage and so I breadboarded it
only to find out the voltage output was no where near the output of 2.4
volts I wanted , despite what the lm317 regulator calculator says so I
wanted 40 milliamps or to be safe just under it so I used the lm317
current regulator calculator and the resistor I entered got me 40
milliamps but when I bread boarded it I got no where near it . so the
best way to go is may be to modify an already existing laser power
supply for a laser diode I know nothing about to try get the 2.4 volts
at near 40 milliamps so ill include one here can you modify the circuit
to deliver 2.4 volts dc at near 40 milliamps for me and powered from a
nine volts battery . thank you swagatam I hope you can get it right
where I've failed .
The required laser pointer driver circuit was actually very easy to design, thanks to the versatile 317 IC, you can do almost anything with this chip.
As shown in the figure, a single LM317 is used for acquiring the required precise 2.4V output at 24mA current.
It's a standard 317 variable power supply design. The preset P1 is used for setting up the 2.4V output.
Or alternatively P1 may be replaced with a fixed resistor of 110 Ohms, which would yield exactly 2.4 volts at the output
R3 is adjusted for getting the 24mA threshold current limit.
As per the formula, the current control resistor R3 may be calculated in the following manner:
R3 = 0.7/0.024 = 29 ohms.
thank you very much swagatam ill give that circuit a go to just have to
round up the resistors I need out of a draw full of them and the 110
ohms isn't an easy one but resistors are never the exact values these
days that's why they have the gold tolerance bands they are either
above or below there values , and also due to the various calibrations
of digital meters they don't all read the same values so anyhow 110
ohms is close to 120 ohms is a try and electronic
calculators and theory circuits don't calculate values using the gold
tolerance bands so the actual results are not known till the actual
circuit build is done or the resistors are measured to the present
calibration of the meter you use to test them with ,thanks swagatam
pal ill get back to you soon hopefully the red 10milliwats laser diodes
hold up ok and at just over 6 dollars each I have 2 only so ill try
More Feedback from Mr. Steven
here's a copy of the modified laser driver circuit you once emailed my back can you modify it again to be adjustable up to 1.2 amps max and minimum of as low as you can get it , as I want to build another but with a higher adjustable current
here's a new printed circuit version I made from a schematic from the laser pointer site this is for the ddl laser driver circuit , its a test load circuit for that so you can adjust the ddl laser diode driver and use the next circuit the test load circuit for that to tune this ddl laser diode driver I think its for 2.8 volts laser diode or near that
here's the latest swagatam, I've made a printed circuit of another ddl laser diode driver from the laser pointer forum so I've added a new feature to it to solve the laser diode damage problem caused by an undischarged electrolytic capacitor in the circuit near the output to the laser diode even though I got the same thing when I blew my test laser diode when I forgot all about the 10 uf 16 volts electrolytic that caused it . so here is my solution , look at the picture and next to the electrolytic capacitor is a plain dc input socket and I've used just 2 out of its 3 pins so it bridges the capacitor and forms a short to discharge it so to un -short it just pug any plug into it and it opens the short so the capacitor can charge during use of the driver and when you finish pull the plug out to shorten the capacitor again fail to do so would result in the charge left in the capacitor being dumped into the laser diode and thus over volting it and blowing it