There wouldn't be much point in measuring the voltage between Vout and Vadj since it's always ~1.25 volts while in regulation. *So that wouldn't be a very good way to actually measure the current.

There wouldn't be much point in measuring the voltage between Vout and Vadj since it's always ~1.25 volts while in regulation. *So that wouldn't be a very good way to actually measure the current.[/quote]

I beg to differ. That is the BEST way to measure the current (unless one is incapable of doing the math). Ideally, you would measure the resistors to get a precise resistance (be sure to subtract the DMM lead resistance - probably less than an ohm).

The current sink into the Adj pin is in the order of 50uA (microAmps. 1mA =1000uA) so for most cases it can be ignored. Now, where does the rest of the current go? - you guessed it to the LD.

As you have noted, the voltage drop between Vout and Vadj is NOT always 1.25V. There are many times when folks here have not supplied the driver with a sufficient voltage overhead. In addition, when these poeple use their DMMs in voltage measuring mode, they are less apt to cause a short by forgetting to change from current mode to voltage mode.

Now, if you do not have access to the sense resistors, by all means use the DMM in current more (10 or 20A scale) on the battery side of the driver.

There wouldn't be much point in measuring the voltage between Vout and Vadj since it's always ~1.25 volts while in regulation. *So that wouldn't be a very good way to actually measure the current.[/quote]

I beg to differ. *That is the BEST way to measure the current (unless one is incapable of doing the math). *Ideally, you would measure the resistors to get a precise resistance (be sure to subtract the DMM lead resistance - probably less than an ohm).

The current sink into the Adj pin is in the order of 50uA (microAmps. *1mA =1000uA) so for most cases it can be ignored. *Now, where does the rest of the current go? - you guessed it to the LD. *

As you have noted, the voltage drop between Vout and Vadj is NOT always 1.25V. There are many times when folks here have not supplied the driver with a sufficient voltage overhead. *In addition, when these poeple use their DMMs in voltage measuring mode, they are less apt to cause a short by forgetting to change from current mode to voltage mode.

Now, if you do not have access to the sense resistors, by all means use the DMM in current more (10 or 20A scale) on the battery side of the driver.[/quote]

IMHO: You are not measuring the current to the laser diode by measuring the voltage across the Vout and Vadj pins. *You are measuring the LM317's reference voltage which is spec'ed at 1.20-1.30 volts. *The math would have been done when the resistor was selected. *Yes, there is something wrong if the voltage is anything other than 1.2-1.3 volts and yes, assuming the resistor is (still) at the intended value, the math will still come out right. *But I maintain it's not a good way to measure the current, especially when you have a DMM capable of measuring current. *Lastly, a slip when putting meter probes on the LM317 pins could easily kill the LD.

So I guess we'll have to agree to diasagree...

There wouldn't be much point in measuring the voltage between Vout and Vadj since it's always ~1.25 volts while in regulation. *So that wouldn't be a very good way to actually measure the current.[/quote]

I beg to differ. *That is the BEST way to measure the current (unless one is incapable of doing the math). *Ideally, you would measure the resistors to get a precise resistance (be sure to subtract the DMM lead resistance - probably less than an ohm).

The current sink into the Adj pin is in the order of 50uA (microAmps. *1mA =1000uA) so for most cases it can be ignored. *Now, where does the rest of the current go? - you guessed it to the LD. *

As you have noted, the voltage drop between Vout and Vadj is NOT always 1.25V. There are many times when folks here have not supplied the driver with a sufficient voltage overhead. *In addition, when these poeple use their DMMs in voltage measuring mode, they are less apt to cause a short by forgetting to change from current mode to voltage mode.

Now, if you do not have access to the sense resistors, by all means use the DMM in current more (10 or 20A scale) on the battery side of the driver.[/quote]

IMHO: You are not measuring the current to the laser diode by measuring the voltage across the Vout and Vadj pins. *You are measuring the LM317's reference voltage which is spec'ed at 1.20-1.30 volts. *The math would have been done when the resistor was selected. *Yes, there is something wrong if the voltage is anything other than 1.2-1.3 volts and yes, assuming the resistor is (still) at the intended value, the math will still come out right. *But I maintain it's not a good way to measure the current, especially when you have a DMM capable of measuring current. *Lastly, a slip when putting meter probes on the LM317 pins could easily kill the LD.

So I guess we'll have to agree to diasagree...
[/quote]

I would measure the voltage at the resistor (less chance for slipping) but you do make a good point .

My concern with using the current mode is the mistake that a lot of people make by using the mA scale. That introduces a resistance (sometimes up to a few ohms when you include the DMM leads) that can affect the circuit operation due to the voltage drop across it. This can cause the driver to go out of regulation if the voltage overhead is insufficient (as we have already seen numerous times on this board).

Alternately, one could insert an R1 or an R05 resistor in the loop and use that to calculate the current.

Having said all that, I often use both methods for current measurement - it depends on how sensitive the driver is to battery voltage. What is important here is that the folks new to electroonics make the effort to understand what they are doing and how the circuit works. Sometimes the journey is more fulfilling than the destination. Cheers,

Paul

fantastic!

hi daedal im one of your fan using your diy regulator for LD, i built blu-ray running quite good using your LD driver, im now on going to build for the first time DIY dvd laser using LG 16x burner, about the battery is it recommended to use 4pcs LR44 to have 6v input power or something like 2pcs CR2? please help me to build this one well, thanks. i have my pic of my casing i will use to the DIY dvd laser burner, check it out.

Well, I almost gave up on this, my diode short circuited when I assembled everything together, the pins on the diode twisted together when I tried to assemble it. > But I should be getting my new diode in a few days, any suggestions on how to prevent the pins from twisting together? Thanks!

Depends. Do you have a hot glue gun? That is quick and easy. Heat shrink can help, tape if you are really desparate. But I think I am going to start using Plastic Epoxy. Regular epoxy will probably be fine too, but the plastic epoxy I got at Home Depot seems to really work well.

Ugg!!! This diode I just ordered must have touched again also! And I even used hot glue! WTF? UGG! I give up! Another 20 some dollars wasted! Can someone please help a brother out building it?!! Im sick of this thing, I have all of this, but I give up on the dang diode.

Anyone? :-[

I don't know what it could have touched. Maybe you are running too much current into it. There are some reported problems with the SenKat diodes lately. Best suggestion I have is to get a heatsink from Jay, and harvest an open can diode from the Sony burners that are on sale.

I think the problem is that the silver solder wont like to get a good grab on those brass pins, and when they pop off, then retouch the LD pins, the capacitor discharges into the diode :-[ This might be the cause? Now where can I get an open can diode on ebay? Or whats the best dvd drive on ebay for harvesting open cans? Thanks! ;D

You need to use a little soldering paste. I am not a big fan of silver solder. I use plain ol rosin core solder and don't use any paste.

The best deal on the Sony drive is from Newegg.

http://www.laserpointerforums.com/fo...num=1202158967

I think next time Ill put heat shrink tubing over my connections to the pins

Oh hey, also, where do I get a module that is not acrylic lens? I want to try a glass lens, or is there an adapter that screws in the axiiz module to make it a glass lens? Thanks!

You can get a glass lens for the aixiz module from Dr. Lava, amkdeath got one for 6 bucks, here are some pics he took:
http://www.laserpointerforums.com/fo...9846835/75/#89

This is how my meter is. So how can I get it to say 245-250ma like my previous pics? Something is up here.[/quote]

Where did you get that Multi-Meter? Mine broke a few days ago and was wanting to get a new one. Yours looks fairly nice!

So I ordered a pair of diodes off of ebay (I would include the link, but I'm too new), and I was hoping to get some opinions/estimates about a safe current to aim for with this MXDL setup. Basically what resistor to use and what I can expect for laser output.

The numbers from the data sheet:
Max Values 150mW CW, 300mW Pulsed

The "Tested" section on the sheet says 80mW at 150mA. I'm pretty sure this is CW.

I was hesitant to order a diode from stonetek with the recent JL VL business, hopefully these work out ok.

So any suggestions on a safe input current?

Two more posts and you can post the link, but you can always post the item number. If they are rated at 150mw's cw then it will take appx. 250ma's. I would need to see the auction to be sure.

Here you go. Thanks for the help!

http://cgi.ebay.com/658nm-RED-DELUXE...QQcmdZViewItem

Assuming the specs he posted are accurate, I would treat it just like the SenKat diode. Running it with 250ma's will give you an output a bit greater than 150mw's. Note: this might still kill the diode.

If you want to play it safe, use a current of 160ma's or so. The diode will still be a pretty darn good burner. You would need a 7.8 ohm resistor. So I would wire up the 317 with a 5 ohm resistor and put a pot in series with it.

Going to be tough to fit a pot in there with the 317, maybe I will have to order a smaller version from digikey or mouser after all. Thanks again for the help.

I need some help please. Just got most of the parts to build this bad boy but what I want is to use 2 cr123s 3.6V (7.2v total) with about 420mA at 3 volts output. I know if I use a 3 ohm resistor it should give me 416mA but the with 7.2v input it will give me 4.2v output right? Now here is where I'm stuck, I can't find a 3 ohms resistor so what combinations can I use to give me that 3 ohms range? All the resistors I can find are 33, 20, 15 and 10 ohms (1/2 watt). With what I have I know I can get 2.5 ohms but this will give me 500mA and that is too high. Also how can I bring down the 4.2 volts to 3 volts? Do I add a pot, if so what size or can I add 2 1N400X in series between the V-out (LM313T) and the 3 omhs resistor? Please keept in mind that space is very limited and with a heat-sink there is really no space at all. Thanks for the help inadvance. :-/ :-[

Your voltage will be right using 2 X 3.6 volt RCR123 rechargeable batteries. The LD will need 3ish and the driver will use over 3 as well. We have been using just a single resistor, no pot for the MXDL at this power. If your going to use this MXDL that DDL has shown here, and you are talking about a 3 ohm resistor, I'm sure you are going to use an open can diode. You may want to pick up one of my heatsinks. If you want the heatsink, just remind me, and I will give you a 3 ohm resistor with it. Also, the stock MXDL has a resistor. It usualy is a 3 ohm resistor. You will have to check the color markings, and compare here: http://samengstrom.com/nxl/3660/4_ba...e_page.en.html If you are interested in the heatsink, check here: http://www.laserpointerforums.com/fo...m=1202452073/0 Have fun with your build!...
Jay

Hey Jay that looks great, wish I was not short on cash right now. Any way I'm still waiting on parts from aixiz, can't proceed with project without the blank housing. Any one have problem with order being shipped in a timely manner? It has been 22 DAYS from the time I order and paid for the parts.