The Adjustable Voltage Regulator

[jtbarclay]

I don't think i can post links yet, but I thought this might come in handy for some of you.

rason.org/Projects/regulator/regulator.htm

 

[a_pyro_is]

That is a good link, but a laser diode should be driven at a constant current not a constant voltage. You can use the 7805 as a constant current supply, but it requires a much higher voltage than the LM317, it is also much less stable.

 

[JECS]

not gonna hurt to run off a constant voltage either. the less ripple the better. if your driver has constant current and constant voltage all the better. then you can use a 9v or something to get more use time before a charge or toss. you could use a lantern battery or something. the psu im using right now has both adjustable current and voltage so it lets me fine tune for burning or if i just want a nice cool run.

 

[a_pyro_is]

JECS, I don't think you quite understand how a diode functions. At a given voltage and temperature it will operate at one certain current. So if you drive it with a constant voltage, as the junction changes temperature the current will also change.

There is no point in adjusting both the current and voltage to a laser diode. For instance, if you have your power source into a voltage regulator, which then feeds a current regulator, if you lower the voltage until the power to the LD starts dropping all you are doing is causing the current regulator to drop out of regulation.

Have a look here and PM me, post in the Help & Repairs board, or post in the thread there if you have any questions.

EDIT
Could an Admin please fix this link as I believe it does fall within the bounds of the forum rules? If this is not permissible, please PM me and I will correct this post.

 

[Gazoo]

Yup, it is surprising how much the output of a diode will drop as it heats up even when the current is kept constant. I didn't realize it until after I received my LPM-1 and did some testing.

a_pyro_is:

I do not understand why you are referring anyone to another forum for info...all the info is here as well.

 

[JECS]

i understand perfectly how diodes function. like any other light emitting component the more/less you put in the brigtter/dimmer it will be. i dont have a current limiter attached to my circuit yet. i run it off a variable amp/volt psu that i made when i was in high school. it lets me change exactly what amperage/voltage going through my diode. i can put anywhere between 2.5-13 volts and 5 preset amperage settings (i dont remember what they are it, was 5 years ago?)
so i can have my diode running off 3v and 250ma or 5v 250ma or 3v 350ma etc etc. that way i can turn things up or down as i please so i can have it run cool or have it burn stuff really quick

 

[Gazoo]

If you do not regulate the current, and instead use a voltage regulator, then as the diode heats up it will also draw more current. I do not know if it would do the thermal runaway trick, but I don't want to find out. You are regulating both the current and voltage with your PSU...this is fine because you need to apply enough voltage to get the current you want to use for the diode, and I am sure the current on your PSU is regulated.

 

[danq]

Jecs, what hasn't been said yet explicitly is that the LD itself is somewhat of a voltage regulator. At a given current and temperature, the voltage across it will be fairly constant - but not the other way around.

So if you 'give' it 5 volts, and it 'wants' to be 2.6 volts, it's gonna be 2.6 volts and it will draw as much current as it can get on its way there. So if your regulated supply tries to keep 5V and is limiting the current to 250mA, then that diode is going to draw 250mA
(and if the current is 'limited' to 500mA at the supply, you'll have a LED instead of a LD .

That 250mA limiting is probably ok for a burner diode, but not so great for a blu-ray -- so depending on what you're driving with that you may want to do some testing and find out exactly what your current-limiting ranges are.

DanQ

 

[JECS]

i did test... i have 2 separate knobs for amperage and voltage. i turn them both up and down until i get my brightest possible dot. i know its the brightest because once i go any higher it dims, so then i just turn it back down so it goes bright again. my voltage and amperage are both regulated by my psu that plugs into the wall. i do this only when im burning things, otherwise i just keep it on a lower setting. i dont have any sort of digital readings but i know when my diode is getting too warm because at certain voltage increments on my psu an led will light up and when it starts getting too hot it will go down one step. i dont have any sort of heat sink right now either besides the aixiz housing.. need to move first so i can make my furnace and make some aluminum ingots

dont worry about me i know what im doing. i was just saying that a voltage controlling pot isnt useless.... there are reasons why some people might want to have it. its like an overdrive, because i have my psu amperage on the highest setting so in order for me to get the dot any brighter i have to adjust the voltage..

 

[Gazoo]

If the diode does begin to dim as you apply more current to it then your PSU may be reaching its threshold. Also another thing I have noticed is when I am wearing goggles, the dot get's dimmer when I turn the current up past a certain point. However without the goggles, it is actually getting brighter, and of course so is the beam. And it will keep getting brighter until it dies from COD. ;D

 

[JECS]

i keep my amp knob on the max its setting (whatever that is) and turn up the voltage until the diode dims then turn it back down to get the maximum brightness.

who said anything about goggles or maybe x_O

 

[a_pyro_is]

a_pyro_is:

I do not understand why you are referring anyone to another forum for info...all the info is here as well.

Just the most recent place I posted that info. It is all in one place and I believe it is easy to understand, but the link has not yet been fixed.

i keep my amp knob on the max its setting (whatever that is) and turn up the voltage until the diode dims then turn it back down to get the maximum brightness.

who said anything about goggles or maybe x_O

Well, just be sure to post when you next fry a diode.
The best way to drive a diode, be it a LED, a laser diode, or any other type, is by constant current. But especially with a laser diode you must have constant current. A constant voltage supply just doesn't cut it.
You have been warned; but by all means, do as you please.

 

[Gazoo]

Well I don't get it...sorry. I mean it would be easy to copy and paste the information over here. But whatever.. :

 

[a_pyro_is]

Well I don't get it...sorry. I mean it would be easy to copy and paste the information over here. But whatever.. :

I guess I've just not the inclination to keep posting again and again the same info. So I'll just post the most current link to the info so long as people don't want to search for it. ::shrugs::

all the info is here as well.

 

[Gazoo]

Whatever dude...I thought you had more character but evidently you don't. I am not going to argue with you, however I don't appreciate your attempt to throw one of my posts back at my face. Have a nice weekend Matt, what's left of it anyway.

 

[a_pyro_is]

And with half a weekend left, back to lasers.