lasorbs... should they have protected my diodes?

[shrad]

hi all

5 minutes ago I had a problem with my dual red

the mount did touch the body of my switching PSU, actually grounded internally

there have been amps flowing from the ground to the anode of each diodes, and the lasorbs fried... yes they are short-circuit

it was only a really brief touch, less than one second, but way more than the tens of milliseconds

now my two 642nm diodes are totally fried, almost dead short, 5.2V for 660mA I wonder if the flexmods are fried too, as they should have maintained the original setpoint

I'm really sad, that's nearly 200€ that went into smoke

do you think these lasorb devices should have protected my diodes?

PS: wires from lasorb to diodes were less than 2" of combined length

[ElektroFreak]

I would think it depends on the type and duration of pulse that hit them. The lasorb is designed to protect against very high voltage buy very short duration transients.. I don't think they'll protect against overvoltage or overcurrent of all types, though..

[daedal]

hi all

5 minutes ago I had a problem with my dual red

the mount did touch the body of my switching PSU, actually grounded internally

there have been amps flowing from the ground to the anode of each diodes, and the lasorbs fried... yes they are short-circuit

it was only a really brief touch, less than one second, but way more than the tens of milliseconds

now my two 642nm diodes are totally fried, almost dead short, 5.2V for 660mA I wonder if the flexmods are fried too, as they should have maintained the original setpoint

I'm really sad, that's nearly 200€ that went into smoke

do you think these lasorb devices should have protected my diodes?

PS: wires from lasorb to diodes were less than 2" of combined length

This has happened to someone else on the forum a few days ago. I'm not sure about the LASORB being a short as is your case. Can you please PM me a few more details regarding this? I'd like to work with you on retesting and re-simulating this issue, and will then forward the detailed results onto Pangolin.

I can completely attest to the amazing operation of the LASORB... I have tested it personally, and Pangolin's videos do show a great repetitive test that a LASORB device survived.

Although, note that the LASORB can protect against ESD, but will most probably not do anything to protect against a driver pushing out too much current to the diode.

--DDL

[drlava]

Hi Shrad, it's sad to hear of the accident. In this case, the lasorbs cannot be held responsible for two reasons.. one - the lasorbs should be no further than 1cm electrical length from the diode for total protection. Two, the energy that a lasorb can absorb is limited, definitely a shock like you describe would destroy one.

It's possible the diodes would have survived if the lasorb was directly across the leads if it was a red formulation lasorb, and if the lasorb failed to a short without going open-circuit in the process. If the lasorbs were blue formuation then they cannot help in the overcurrent condition, only static.

The FlexMod should be OK if the potential was just 5.2V.

[shrad]

thanks for your support all

the power supply is one of those where there is apparently a connection between the positive lead and the phase, as there is a huge potential between them

here the base plate holding the modules (connected to the diode's body, cathode and not anode like I said earlier) has touched briefly the case of the power supply

it led to a massive current flow from cathode to anode as the flexmods are common anode (if I'm right)

in my case the flexmods seem to be dead as they feed 600mA to the diodes where the original setting has not been modified

I don't know why, I was assuming a 2" wire length was still in the safety range for the lasorbs, and as they have been shorted out by the massive current flow, they would still have absorbed the surge

I'll test the diodes again later, for now djolek just left my house from a small laser engineering session and I feel a bit tired

EDIT: I'm not blaming lasorb operation in any means, I'm just trying to figure out what went wrong and how, because it is a bit hard to tell for now

[ElektroFreak]

I wish we had some numbers on just what kind of duration of excessive current or voltage the lasorb can divert to ground before it becomes a casualty and thus any components attached. I haven't seen a datasheet for the lasorb myself, but I would imagine it will only work with extremely short-duration surges similar to what an ESD discharge would produce. A longer duration overvoltage/overcurrent might easily prove too much for the lasorb since to my knowledge it's not intended to protect against them. Even a switch transient will be of a very short duration since they are usually caused by a tiny arc occurring as the switch contacts meet.

[sbk]

Death of red diodes is always sad to hear...

It it can help, the best way I found to protect the diodes from overcurrent (exemple : shorting the case to ground) is to power the diodes's driver with just a little more than the required voltage to run the diodes at full power. So 5V for my quad red, as they are in parallel operation. If you make a bad manipulation, you will have 5V on the diodes instead of the ~4.5V they usually eat... Just be sure to not have a short circuit of more than a few seconds.

Works great, I accidentally verified this by shorting the cases more than one time

[shrad]

that's a nice addition to the general knowledge, thanks

but I still don't know how it happened.. I think I'll drop these switching power supplies and design a linear model with the toroids I have...

I'll dismantle an old tek scope to get a nice casing with plugins

anyway, I take that as a lesson and an experience, and I'm not too much sad... the only real hard is the wallet... nearly 250€ that went in smoke

[RedlumX]

Well, another one. I am sorry to hear. I have seen countless cases like this again and again, because this is intrinsic to the design. If the driver would not drive the diodes against "plus" but to "ground" instead, the diodes would still be alive. This is exactly what I tried to say here, for very good reasons.

[Pangolin]

Hi all,

Just a few brief notes.

One point is that I am still at the Prolight & Sound conference. In preparing for this tradeshow, I have not been on PL in weeks. And after I return, there will be some client follow-up which will keep me away from PL for another few weeks. I would not have become aware of this post if not for another client who contacted me and pointed me to it. This is a prime example of why I ask people to contact Pangolin directly with problems, rather than making posts on forums (not that I am unhappy with this thread -- just giving further information and reinforcement for my past statements of how, and why to contact Pangolin directly).

Second, I say that LASORB is like a bullet proof vest. These keep military and police officers safe from flying rounds and the like. But a bullet proof vest will not help you if you step on a land mine... There are limitations to what LASORB can do...

Third, there is most definitely a "surge conduction time" which represents a kind of maximum time that LASORB will remain active. This is generally on the order of milliseconds or so (I can't remember and don't have easy access to the data sheets right now). But a surge which lasts for the better part of a second would most definitely be there for longer than the maximum time that LASORB will protect the diode.

Also, the fact that the LASORBs themselves are shorted is truly remarkable. It tells me that the surge must have lasted longer than you are thinking. The reason I say this is because we have clients using LASORB to protect their 808nM diodes that operate from 5V supply and driven at a few amps. Sometimes these diodes "go open" (from poor manufacturing), at which point in time all current will be flowing through the LASORB. What my customers tell me is that LASORB will get hot, but still not really short or do anything else undue. So it's really remarkable that you were able to short one or two. It could be that your supply voltage is much higher than 5 volts, and so this caused a really high amount of current to flow through LASORB (probably after the laser diodes themselves went open). Of course, all of this is just guessing without me seeing the damaged parts and performing tests with our own test equipment.

Best regards,

William Benner