Great info auto! exactly what I needed to hear. I wish I had a variable bench psu, unfortunatly i have the option of 12v or 5v. I may step down to 5 in this case though. I got the aixiz module today and am waiting on a new diode from modwerx, im out of burners to harvest from so it'll be a good week before any updates but hopefully I'm fairly well set to go when the diode comes in though. I figured I could throw a resistor in there but I like the idea of being able to adjust it too .
**Edit**
I was just at radioshack, I didn't see any pots that would be low enough, but I did see one that was labled as a 25 ohm 3 watt reheostat (looks just like a pot), what exactly is that? would that work in this circuit? I like the idea of having a pot knob on the outside of the box.
I hear ya about the adjustable resistance bro. I thought that would be pretty important when I first got into lasers.
Made two DDL circuits with pots and found that they got hot depending on the diode I was powering. The 445s are too much for a pot so I started making fixed resistor DDLs with a 1N540* diode, a 2W resistor and a LM350 instead of the LM317.
Everything worked great but they are hard to build small if you want to put it into a handheld.
Remember your Ohms law if you do chose fixed resistor values.
A 1ohm resistor will give ~1.25A, 0.5ohm will give you .625A etc.
I'd pick something about 1/3rd less than the maximum people have tried for a specific diode and just set it to that current, should give fairly long life before it kicks the bucket
think of a test load as a diode simulator.
The difference is: instead of producing light, it provides a load (and a bit of heat). If you screw up and hit it with 5 amps for a few seconds, instead of costing $50 for a diode, you go "oops" and fix your mistake.
If you are making drivers....I'd really recommend having a good one.
Most use low wattage resistors and diodes but I prefer to be able to leave mine hooked up for a while even with a high power build.
I made two with 1N4004 diodes and low watt rated resistors but they got hot REALLY fast with my 1st 445 build.
Gotcha, I understand a bit better now lol. That'll have to be my next project. i read a bit more on the lm317 circuit tutorial and I didn't see anywhere about stepping up the current. I'm getting 240mA when I'd like to get around 400mA+. I have a lpc 815 coming and I'd like to push it as close as I can. Any suggestions on getting this circuit up to 400mA? I know earlier you mentioned the LM333 I believe. I'm testing with my multimeter on the leads where the diode would go, I'm reading now and I guess I wont get a very accurate reading unless I have a dummy load on the 317? correct?
LM350 is just rated to 5 amps instead of 1 (LM317).
You won't get any reading unless you use a dummy load.
For the LM317 (and LM350) the reference voltage is 1.25.
Divide 1.25 by the resistance.
1ohm resistor=1.25A
2ohm resistor=.625A (625mA)
3.125ohm=400mA
Its all math, you need to understand this stuff before you can make electronics that do what you want.
Search:
Dummy loads
DDL (or deadal I think) driver
Ohm's law - Ohm's Law
It took almost a month of solid reading a lot of experimenting to understand most of this with any reliability, don't expect to know it all overnight.
Ahem....
LM317 is rated for 1.5A, not 1A.
You can get a reading without a dummy load, using nothing but a DMM.
It might be a bit less accurate though...
Yeah I took electronics for several years in highschool, But that doesn't seem to be helping much now lol. I don't remember half as much as I should. Anyway with my DMM only I get 12.16v 580mA / 5.08v 9.8A from my power supply. Still getting about 3v 240mA from the 317. I'm a bit lost... lol. I guess I'll try a dummy load today see if that does anything different. I really need to see at least 400mA to be comfortable with it.
The DMM gets a current reading with its own resistor, I read on here a while back that it made the measurement too inaccurate to be trusted.
If you want to increase the current, you can add a fixed value resistor in parallel with your pot. You need to figure out the size you need though
*hint* Two 1ohm resistors in parallel have a resistance of 0.5ohms
You'll probably have to find a company that sells electronic components if you don't want to get your stuff online.
Radio shack has only ever had one thing I needed and I had to modify it to suit my use.
Might be easier to look at it this way:
The diodes dictate how much voltage will be used and the resistor uses current.
I know its frustrating but if there was no reason to do it a specific way, no one would be.
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