PHR-805 doing...nothing?

[sebjf]

Hello,

I have just got my first laser diodes, a couple of PHR-805s; I have connected one to my bench power supply to see if I can get it to do anything, before putting it in a case - but it isn't lasing, or emitting any kind of light.

I have it connected to a bench power supply current limited at ~100mA.
I believe it is connected correctly because at this it pulls around 1.5v, whereas connecting in any other configuration there is no circuit.

From my non-existent experience and reading around here I would assume the problem could be:

1. The diodes arrived broken - I'm not sure about this, the seller has almost perfect feedback and both behave identically.
2. I broke them - possible, I did realise too late that the current reading on my power supply was under-reporting by 10mA but I didn't provide them more than 130mA (one of them anyway), but even in this case they should still emit Something right? Even if I now have £7 LEDs.
3. I can't see 405nm light - well I did think when I was younger I could see the light from TV remotes if I looked hard into the IR emitter so maybe, but I can't feel anything on my hand if I put it in front of them.

My instinct in this case is to give it more power until it does something, but thought better of it and decided to ask here instead.

I know the diodes are not very powerful but looking at images of projects here using diodes of a similar wavelength the difference between them and mine is huge, so I must have something wrong with mine!

 

[weeba2kv]

You need to have atleast 4 volts on 405 nm laser diodes.
TV remotes give IR light not visible for humans

 

[Fretwrecker94]

Build a DDL driver to test one out. You pressed them into an Aixiz module too I assume. I don't know if you are, but try to avoid using alligator clips with diodes when you test them. If you absolutely must, solder leads onto them and attach the clips to the leads. That reduces the possibility of a short.

With a DDL driver you need about 7.5V to power one. That's just because you need to factor in the LM317's operating voltage.

 

[AnthoT]

Build a DDL driver to test one out. You pressed them into an Aixiz module too I assume. I don't know if you are, but try to avoid using alligator clips with diodes when you test them. If you absolutely must, solder leads onto them and attach the clips to the leads. That reduces the possibility of a short.

With a DDL driver you need about 7.5V to power one. That's just because you need to factor in the LM317's operating voltage.

Yup those are the simplest to build and they only cost about 1$ at most. But you could also turn the voltage up to 4.5V at 100mA on your Bench power supply and then it'll likely work.

 

[TheReddish]

"whereas connecting in any other configuration there is no circuit" that part bothers me. I would go with option 2

 

[sebjf]

Hello, thanks for all your replies!

If you could all bear with me, but both the DDL driver and my power supply (when set correctly) are constant current sources, so the voltage output will be dependant entirely load which is my diode; according to this site (Laser driver - It can be done) the blu-ray diodes should drop about 4v, as weeba2kv said, but at 100mA my (current limited - the open load voltage is set to 6v) power supply is only driving ~1.5v, making the equivalent impedance of my diode about 15ohm at this current. So unless I am missing something there is no way to drive it at 4v without putting too much current through it, right?

(I was joking about seeing remote signals - well half joking, someone in another thread said that peoples sensitivities can vary dramatically at the ends of the visible spectrum, and I've never seen a violet laser before so don't know how bright it is meant to be, so did think it may be that I just couldn't see it!)

 

[TheReddish]

(I was joking about seeing remote signals - well half joking, someone in another thread said that peoples sensitivities can vary dramatically at the ends of the visible spectrum, and I've never seen a violet laser before so don't know how bright it is meant to be, so did think it may be that I just couldn't see it!)

I see 405nm as a harsh white beam, with a neon blue glow, but cannot see 808nm at all, not even the the little faint red dot. so I get your thoughts there and it does happen. Of course me being overly sensitive to UV and playing with lasers is not wise, I will have cataracts most likely from it when I get older. I noticed this after my lasik surgery, the doc had to use special blades cause he said my cornea is way to thin, and I cannot have my eyes adjusted again ever.

 

[DTR]

Just to make sue are you using this pinout to power the diode.

Also here is how I power laser diodes with a bench power supply. Start with nothing connected to the power supply, turn it on and turn the current to zero. Set the voltage to 4.5V(for your diode) and turn the power supply off. Short the output leads on the power supply together than connect your diode. Turn on the power supply and adjust your current to your desired level. It is the same as with the 445 in this video. If it does lase but you need more headrooom with the voltage as it caps you at a certain current which is lower than your desired then repeat the process and up the voltage in 0.1V increments until you get the desired result.:beer:


If you don't follow this process and leave the voltage higher than the max forward voltage for the diode and the current @ zero it is possible to have a spike when you turn on the power supply that could kill the diode. With both the current and voltage set below the max the diode can handle this will reduce any chance of the diode getting a startup spike and shorting the output leads is a good habit to get into in case there is a output capacitor in your power supply.

 

[sebjf]

Hi everyone!

See that is what is giving me pause, the pinout above is different to the one with the mini-datasheet that my diodes arrived with. Mine says the diodes are case negative. That in itself wouldn't be odd except there are other things about the datasheet that look out of place, for example, the package diagram shows the diode looking down into the emitter (is that normal?), either that or on mine the positive and negative pins are reversed. It also says the reverse laser voltage is 3v (I believe this is referring to the voltage drop, caused by the reverse bias phenomenon, right?)

That is what I was referring to before when I said "whereas connecting in any other configuration there is no circuit" - the NC pin in the diagram is the lowest pin on mine; I connected my supply to this pin to see if I got them the wrong way round but the supply behaved as if I had an open load, so it isn't connected on mine.

I set up the zero-load limits on my bench supply before connecting the diode, but shorting it out when turning it on is a nice trick - one that I did not think of unfortunately before you told me about it.

I can say for sure though that the setup there is identical, but mine just will not drop more than 1.2v at the specified current. I did what weeba2kv said (though Definately not what was meant ) and put one of the diodes up to about 700mA to see what would happen. At this point the voltage was ~4v, and I could melt plastic - but not with the laser.

So I am still rather confused, the last diode is certainly dead but its electrical response remains unchanged from when I first connected it up, and the response from both was identical. I must've broken them but am concerned I don't know how! The only thing I can think is a spike when I first turned them on as I had the current limiter set right to 0 (however, the voltage was about 2v (as in open load limit), and it also doesn't explain why they don't emit any light at all, do all diodes turn into expensive LEDs when you burn them out, or is it random? or depends on the damage?)

 

[Zlasersinc]

Wait... You "connected" a wire to the laser diode or "soldered'? If you used aligator clips on those tiny LD pins that could be a problem. It is very easy to short out that way.

 

[sebjf]

*Looks really, really, really, REALLY sheepish...*

OK, so I figured out what I did.

Turns out the mini-datasheet diagram was not mirrored as I thought, but rather, 'Not Used' =/= 'Not Connected'. I used the measured power consumption of my supply to tell whether there was a circuit, and judge the behaviour of the diode (e.g. voltage limited == open load). When I originally connected my diode there must've been a loose connection because my supply indicated open load, so I moved my probe over (onto the NC pin) and measured current draw. Thinking that the Not Used pin would not be connected to anything, I assumed whatever was dissipating the power must've been my diode, the data sheet was reversed, and that it was simply not lighting.

Just now I went to connect my supply again across the non-case pins as DTR's diagram shows (I did try that but I couldn't remember if I tried both polarities) and it lit up!

So...its probably still a £7 LED what with all the abuse like the 0.7A heating the case to 100deg, but at least I know what I did, and the other one may still work.

Sorry! But.. if you all hadn't kept prompting me to keep looking at it I would have given up on them ages ago so Thank You!

(I will now use my laser to engrave something about 'assuming' 'ass' and 'me' on my forehead...)

 

[mikesnap99]

[deleted] Sorry missed a line

Mike

 

[Sigurthr]

Just to make sue are you using this pinout to power the diode.

Are you sure, DTR? I'm fairly certain PHR-805T's use the LPC-815 pinout (case negative). I just built one not two weeks ago and it was definitely case negative as I clipped the bottom "PD" lead.

AFAIK it's only the 445/450 blues and the 12x 405's that are case neutral.

 

[mikesnap99]

^^^ your right! I knew something was wrong with it. They are the same pin-out as the LPC's.

 

[Fretwrecker94]

Sigurthr is right. I've done many a 805 builds an theyre all case negative. But to add to your post, SF-AW210's use a case neutral design. And I'm pretty sure the GGW's do as well. The 803's pinout is neutral too. 805's are different

 

[DTR]

Yep you are right. I mixed up the 803 and 805. I got the picture here on a thread about the 803. Good catch.
http://laserpointerforums.com/f38/phr-803t-new-build-not-lasing-71027.html#post1023789