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Digital laser PSU

kiyoukan

kiyoukan

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I have been looking to build a digital power supply for lasers and other things.
Now i have been thinking very hard about a good and controlled way to do this.
My thoughts.
use 2 lm317 or equivalents.
then use 1 of these to control them
Digital Potentiometers http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCP4241-502E/P-ND
This has 2 resistors that i could control via my arduino.
the first lm317 would be a voltage regulator while the second would be a current regulator.
i have heard pwm driving a laser is bad so these would allow me to control the lasers power safely with no spikes or worry about the slider jumping in a normal pot.
if you have any better simple ways to do this that would be safe for a laser please let me know.
my only concern is what resolution do they have as it would need to be very precise.
 
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MarioMaster

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This would be a good way of making a constant voltage power supply, however the digital potentiometers are quite limited in output current. In current regulation mode the LM317 sinks a lot of power through the resistor and it would probably burn out the digital potentiometer; so it would not be quite as easy for current regulation.

The chip you linked for example is limited to 25mA.
 
kiyoukan

kiyoukan

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Would there be a better way i was reading something about a r2r ladder.
I have been thinking of a way to regulate power besides using pwm.
Maybe a bjt im kinda new to this.
it almost seems it would be better to use a normal pot and a geared stepper motor. lol
 
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Seoul_lasers

Seoul_lasers

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kiyoukan said:
I have been looking to build a digital power supply for lasers and other things.
Now i have been thinking very hard about a good and controlled way to do this.
My thoughts.
use 2 lm317 or equivalents.
then use 1 of these to control them
Digital Potentiometers http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MCP4241-502E/P-ND
This has 2 resistors that i could control via my arduino.
the first lm317 would be a voltage regulator while the second would be a current regulator.
i have heard pwm driving a laser is bad so these would allow me to control the lasers power safely with no spikes or worry about the slider jumping in a normal pot.
if you have any better simple ways to do this that would be safe for a laser please let me know.
my only concern is what resolution do they have as it would need to be very precise.
Click to expand...

Forget the idea and go with the Die4lasers driver. It is able to have current monitored while laser is in full operation.
I am nothing short of impressed with this driver!
 
kiyoukan

kiyoukan

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That will let me regulate current but not voltage.
I am after both.
 
Seoul_lasers

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you need a adjustable power supply then. The driver is a current regulator.

My setup is pretty much what you are after.
 
MarioMaster

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I'm pretty sure he wants to build one, not buy one. I have a current and voltage clamping psu and it's amazingly handy but I don't have any diagrams or anything to help you out :(
 
HIMNL9

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you can use the current sink configuration, and drive the reference pin with the digital potentiometer .....

Too late today, have to run ..... maybe tomorrow i can post something more precise ;)
 
kiyoukan

kiyoukan

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oh himnl9 i am awaiting that very much i did find something tho.
http://www.ibiblio.org/pub/linux/do...s/common/src2/article389/powersupply_upd3.gif
Can someone confirm if this is what i want?
powersupply_upd3.gif
 
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Meatball

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Getting a digital pot to work with the good ol' LM317 would be ideal for my setup as well. Thanks HIMNL9! Can't wait to see what you've got in mind! :)
 
L

LSRFAQ

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Meatball said:
Getting a digital pot to work with the good ol' LM317 would be ideal for my setup as well. Thanks HIMNL9! Can't wait to see what you've got in mind! :)
Click to expand...

Be weary of the undefined states in digital pots as they switch settings or go open circuit at startup.

Winfield Hill has a excellent writeup of what happens when a 317 does not see that 1.25 uA current sink on its control lead. You can get 1 Mhz oscillations while the 317 waits to settle back down. It happens with analog pots too, as the wiper lifts off the resistive material in multiturn potentiometers.

You wont know till you try it and test it, but make sure you get one that remembers its last state.

Steve
 
Meatball

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Yeah, after doing some research it appears that these can be used for just about anything except for a laser driver. A wire-wound coil is about as safe as it gets. Something like a stepper motorized pots would almost be more ideal in this case..
 
kiyoukan

kiyoukan

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Well i got some great news.
I found out i have a blood relative who works at ST micro electronics.
He already got me a "Sample order" of 50 lm317 and said if i ever needed any other part from ST to just send him its model and he will get it.
So Are there any good ics for driving lasers from 90mw to 1w?
I am so excited i just sent him a request for A sample order of there ST7 micro controllers with 32 I/Os
So if any one could help me find some parts and stuff that would be great.
 
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