Stan_Ham diode driver (analog)

[The_Doctor]

Bill, I see this on the Lasorb site page about the device: "When activated, the voltage across this portion of LASORB will not exceed 2.2 volts, even during 50 amp ESD surges".

What's the peak voltage across it instantly prior to triggering and how long does that peak persist at over 6V (assuming it ever reaches that value)?

Also, does it work ok for 405nm diodes whose Vf is a volt or two higher than most other laser diodes? From what I can see, a Lazorb would be triggered by their operating conditions unless it was ok with letting around 4V reach a laser diode. So my main question is, how high a voltage does it allow to reach a diode without triggering?

[carmangary]

I've heard of very good results from using multilayer varistors for these types of applications. They are available in tiny SMD packages so they might be worth investigating if anyone is interested. It's something to think about until the Lasorber is available.

I've never had a DVD or CD reader/burner die from static which makes me wonder why our modules are so susceptible to that type of damage. Why is that? Is it because the diodes are so exposed in our modules?

[The_Doctor]

It's because any significant increase in current (as driven by ESD or any other surge) increases the optical energy at the cleaved facet to the point where damage results, and once it starts, the damage escalates exponentially at extreme speed. I also reckon you got lucky. Maybe you're rigorous in mouning them securely too. Another reason is that DVD diodes have grounded cans, the problem can be worse when you have to isolate a can from the chassis.

Re varistors, I agree. Though they might be limited on their own, there are 6V ESD rated types with 0.5 ns response times. I have several. From eBay no less, it's often great for components for diode drivers. (I got low ESR tantalums; tiny 1W 4V7 zeners with low temp coefficient, also good for 5V line limiting protection in driver inputs, lots of each very cheaply). The Lasorb looks good because it doesn't depend on an RC filter preceding any diodes. I suspect you can get close to it with a combination of varistor and fast recovery rectifier in series for forward bias, and fast zener for reverse, but at the asking price, it might not be worth trying to outdo it. Still want to know more detail about how it works though. I mean, exactly how voltages and currents flow in the circuit it's fitted to, before, during, and after triggering.

[carmangary]

Not sure if you understood that I was talking about a DVD/CD player or burner that you would have as part of your home stereo or in your computer. They all have laser diodes but I have never heard of ESD being an issue with them. I don't know if they will hold up to being zapped with a Tesla coil but as far as every day static and normal handling there is no problem. Why is that?

[The_Doctor]

Filtering.
One way or another, there's plenty to reduce the rise time and intensity of an HV pulse if it's applied to the case, or even to the sockets, where it most likely goes to ground. But if you try to hit it where it hurts, it will no doubt hurt, but there will still be other parts to take the flak.

I thought you meant that DVD diodes were for some reason secure in your tests even when fitted to DIY laser mounts..

[Pangolin]

Bill, I see this on the Lasorb site page about the device: "When activated, the voltage across this portion of LASORB will not exceed 2.2 volts, even during 50 amp ESD surges".

What's the peak voltage across it instantly prior to triggering and how long does that peak persist at over 6V (assuming it ever reaches that value)?

Also, does it work ok for 405nm diodes whose Vf is a volt or two higher than most other laser diodes? From what I can see, a Lazorb would be triggered by their operating conditions unless it was ok with letting around 4V reach a laser diode. So my main question is, how high a voltage does it allow to reach a diode without triggering?

It's not really a voltage-triggered device. That's probably poor wording on our web site and I appreciate the question, because it helps to point out that we could try to clarify that part (without giving away the secret during the patent's pendency). One thing you'll notice is that LASORB is quite happy to protect the laser diode whether it is operational or not. And LASORB will, for sure, work with BLURAY laser diodes, or even series strings of laser diodes, although I personally would recommend that one be used for each laser diode in the string.

I've heard of very good results from using multilayer varistors for these types of applications.

Lucent Technologies patented the use of a multilayer varistor to protect a laser diode. I pointed this out in another post. Of all of the ways to protect a laser diode (besides LASORB), a multilayer varistor seemed the most promising, but still, in our testing it was completely unsuccessful at preventing a single 15kV strike from blowing the laser diode. Plus, multi-layer varistors are relatively high capacitance devices. Capacitance well over 1nF is not unheard of. This complicates modulation. LASORB presents almost no capacitance and almost no resistance loading so driving is quite easy.

Bill

[carmangary]

Well, if it works as good as advertised I look forward to buying my first Pangolin product.

[The_Doctor]

I favoured varistors at least for protecting the supply regulator lines rather than the diode itself, but Robin Bowden insisted that a zener would be a better way. There was a little more to it, and I forget exactly what (minimal RC filtering I think, to trap what the zener didn't), but he showed me a video of a laser diode being wilfully zapped with sparks and looking as if it liked it. In fact, the sparks made it lase in flashes when it wasn't powered. I think I lost a load of saved emails, but if I do find that one I'll post details. Robin, if you're lurking, any chance you can post on this? I'll try hunting for that saved mail tomorrow, too late now though.

[Pangolin]

I favoured varistors at least for protecting the supply regulator lines rather than the diode itself, but Robin Bowden insisted that a zener would be a better way.

I don't recognize the name. What's his background?

There was a little more to it, and I forget exactly what (minimal RC filtering I think, to trap what the zener didn't),

Zeners are notoriously slow devices, and, even if they weren't, there is no way to get the zener voltage to match, and then track, a laser diodes lasing threshold voltage.

We tried a lot of zeners at Pangolin, and even specialized TVS devices that were made to be fast zeners. No dice... Nothing held up in the face of 15KV or even 8KV.

Regarding "minimal RC filtering", well, do the math. We present the math on the LASORB web site.

ESD is shorter than 1nS (0.7nS according to IEC human body model) up to around 50nS. So that's around 20MHz to higher than 1GHz. The ESD protection scheme has got to provide an impedance no greater than 44 milliohms in this frequency range in order to be effective.

Remember my powerpoint? A 5cm piece of copper braid that directly shorts the terminals of a laser diode provides only a 50-50 chance of protecting the laser diode. That would be one hell of an R and one hell of a C to beat a 5cm piece of copper braid!

but he showed me a video of a laser diode being wilfully zapped with sparks and looking as if it liked it. In fact, the sparks made it lase in flashes when it wasn't powered.

Yes, I can confirm that this is the case. It is quite amazing that you can "see it" since ESD events last only a tiny amount of time. Even once the laser diode has been destroyed by a first strike of ESD which causes a dead short across the terminals, further ESD evens will still give light output (remember we are talking about 50 amps here...)

I think I lost a load of saved emails, but if I do find that one I'll post details. Robin, if you're lurking, any chance you can post on this? I'll try hunting for that saved mail tomorrow, too late now though.

I thought we were the only ones who had the balls to purposely subject a laser diode to ESD (and Tesla coils). I would love to see the video and also -- more to the point -- love to see the laser actually function afterwards.

Also, the survivability depends strongly on the type of laser diode being subjected to such abuse. As one example -- diode bars that can take 50 amps DC can actually take the 50-amps for one nanosecond that ESD provides. So, in this way, diode bars could conceivably live without "positive ESD protection". But diode bars still need a good protection against "negative ESD" and LASORB provides great protection against negative ESD.

Bill

[dave]

I thought we were the only ones who had the balls to purposely subject a laser diode to ESD (and Tesla coils). I would love to see the video and also -- more to the point -- love to see the laser actually function afterwards.

I have video robin took of his improved diode driver - This one has much more protection, and a switching supply on board.. ll dig it out and post it when i get home From memory Robin was zapping the mod input to test protection.