1+ Watt, Non-aixiz housing, and 405-G-2 lens

jib77 said:

The "-O" is a pin, the ">-" is the socket. Do you know you need a constant current source not constant voltage?

Click to expand...

No I thought V=IR. So the only way to change current would be with the voltage because the resistance is constant (i know it goes up with temperature but i mean you cannot change the resistance). If there is something wrong w/ my logic please explain.

Resistance does change with temp, and you will get thermal runaway in constant voltage mode. That is why we use current sources/sinks for LD and LEDs.

jib77 said:

Resistance does change with temp, and you will get thermal runaway in constant voltage mode. That is why we use current sources/sinks for LD and LEDs.

Click to expand...

Yes I read up on constant current drivers vs. constant voltage drivers and now I understand why I need to use a constant current driver. Thank you very much. You may have just saved my second diode.

What would you recommend I use? And how would I go from the 7.2 volts coming off my batteries? Also how do I know what current to run it at?

The simplest is a LD1085 LDO in current mode:



Make sure the caps are ceramic and rated for 10V or more, and that the resistor wattage rating is more than Iout * 1.25 ... for example, for Iout of 1.8A you need a resistor that is rated for more than 2.25W.

There are also some LED buck drivers that can be modified for use but I cant find the thread right now. These are much more efficient since they are switchers.

445's can be run up to 1.8A. The higher you run it, the shorter the life. If you build a LD1085 circuit I would just use a 1Ohm resistor to make it easy ... it will give you 1.25A.

You also need to keep in mind that laser diodes have a very shallow IV curve. Meaning it only takes a very slight change in voltage to cause a large change in current.

Well I had some success with the current driver. I used a higher current diode (not laser diode) as my RSET. That seemed to work pretty well, although it fluctuated quite a bit with temperature. I got between 1 and 1.3 amps from the current circuit depending on if I put the diode (diode that i used as a resistor) in front of the fan.

The CPU heat sink worked very well and kept the laser housing cool to the touch (I couldn't touch the actual diode).

And when I went from using a power supply to Li-ion batteries I got the same currents and voltages :yh:.

Then the sad part, I disassembled all the wiring and hooked it all back up to clean up all the connections and when I tried to start the laser again the laser didn't shine and the amp meter read 7+ amps for a second before I unhooked it. I since then corrected some wiring and the laser will not start. I think i killed it :cryyy:.

But I'm not for sure would hooking up 8-9 volts to a 5V diode not make it light up and kill it instantly? I would imagine it would at least flash, I didn't see anything.

And pics

But I'm not for sure would hooking up 8-9 volts to a 5V diode not make it light up and kill it instantly? I would imagine it would at least flash, I didn't see anything.

jib77 said:

The simplest is a LD1085 LDO in current mode:

Make sure the caps are ceramic and rated for 10V or more, and that the resistor wattage rating is more than Iout * 1.25 ... for example, for Iout of 1.8A you need a resistor that is rated for more than 2.25W.

There are also some LED buck drivers that can be modified for use but I cant find the thread right now. These are much more efficient since they are switchers.

445's can be run up to 1.8A. The higher you run it, the shorter the life. If you build a LD1085 circuit I would just use a 1Ohm resistor to make it easy ... it will give you 1.25A.

Click to expand...

So if I use a .8ohm 3 Watt resistor and properly heat sink it I should be fine?

zenith828 said:

So if I use a .8ohm 3 Watt resistor and properly heat sink it I should be fine?

Click to expand...

Yes ... that's 1.56A so 2W absolute minimum, 3W is good. Alternatively you can use two 2W 1.6 Ohm resistors in parallel to give you 0.8Ohm 4W.

About measuring with a DMM ... In my experience they usually show an initial spike that is not really there. I get the same thing, but when I hook it up to an o-scope the spike is not there.

You probably killed your diode with ESD, they are extremely sensative. Also if you did not discharge your output cap, it could have had enough charge to zap your diode when you hooked it back up.

What do you mean you used a diode for Rset? Did you mean you used it in place of the LD to set the current? IF so this will not work ... you need a dummy/test load consisting of 4 1N5401 diodes and a 1 Ohm 2W+ resistor in series:

[LD+] ------>|-->|-->|-->|-----/\/\/\/\----[LD-]

Measure the voltage drop across the 1 Ohm and you will get the current indirectly: 1mV == 1mA

Hey guys, it has been a while. I can be frustrating to build a laser so I took a good long break from it and have resonantly finished. The entire build is pretty much the same as before I just bought drivers for it this time because broken diodes were becoming too costly. And as a bonus I added a cheap 5mW laser to the bottom of the handle. And...... pics

What a great build ! Looks like a UZI-laser.

Nice build it does look like an UZI :beer:
-Anthony