The case pin.....

[Kansas Outcast]

Okay, I'm trying to do my homework before I make an attempt at a 445nm build; so I've been looking around the forum, and I cant quite find the answer that I'm looking for. On the 445nm diodes I've read that you have to cross the case pin over to the neg pin; but I've also read this is not necessary for all builds. Why is that?

 

[ElektroFreak]

Okay, I'm trying to do my homework before I make an attempt at a 445nm build; so I've been looking around the forum, and I cant quite find the answer that I'm looking for. On the 445nm diodes I've read that you have to cross the case pin over to the neg pin; but I've also read this is not necessary for all builds. Why is that?

The 445nm diodes (and most blu-ray diodes) are "floating" ie the case of the diode is not connected to ground. This introduces a small amount of susceptibility to static discharge, which can instantly kill a diode. As an example, if you walk around on some carpet in the winter and touch the case of a laser pointer or lab module a static discharge may occur. If the case of a floating diode is not connected to anything, then after passing through the case the discharge must pass through the diode itself to reach ground. This is not good. It has been my experience that connecting the case pin to the negative pin grounds the case, which establishes a "path of least resistance" that routes most static discharges around the diode since the negative connection to the diode almost always connects to ground at some point in a lab system, and in a portable (hand-held) the negative connection is the closest thing to ground.

In certain hand-held installations where the case is electrically isolated so that a discharge cannot get to it under any circumstances then connecting the case to the negative pin is not necessary.

 

[Kansas Outcast]

Thanks for the great explanation, I had always wondered why the case pin had to be connected to the negative in some builds and why you didnt need to in others.. is it just in good practice to do this all the time or can it cause problems when not needed?

 

[ElektroFreak]

I always connect the case pin to the negative pin.. never had any problem regardless of the type of installation.

 

[Kansas Outcast]

Alrighty thanks, I appreciate the help.

 

[123splat]

ElectroFreak brings up a good and scary point which I hadn't considered (thanks Electro).
Another issue that I have gleened from looking at other's build posts and such is: the "Blue" diodes have the Anode and Cathode isolated from the case (as Electro stated). The 'Reds' (been around much longer) have the cathode connected to the case and the other isolated pin not connected (unless the LD has a photodiode in it). Some/Most of the driver circuits used with Reds, and now with the Blues, seem to have a common ground (or negative) path between the V- input pad and the LD- pad. If such is the case, and your host is negative (the battery is in with the Batt- connected to the case, you only need to connect a lead from Batt + to the driver V+ in and tie the LD's cathode to case and connect the case lead to the driver's LD-, and the LD's Anode to the driver's LD+ (only have to use 3 wires instead of four).
Hope I've got it right, if not, somebody will chime in and correct me (but, it has worked for me in three 'Blue' builds. Word of Caution: I there is a warning NOT to do that on one of the Dr. Lava drivers because the V- in and LD- out are NOT connected. Just be sure to read the docs and think out what you are doing before applying soldering iron. Best of luck!