Installing shorting relay on laser diode

[weartronics]

Hi PL,

I have a ViaSho 100mW 532nm laser where the laser head is a separate assembly to the power supply. There is a connecting cable with pins for laser diode, and some TEC and/or thermistor I think. Since I will install the laser head inside my projector but leave the power supply outside, I want to install a shorting relay across the laser diode to protect the diode when the power supply is disconnected.

But, what happens if the power supply is accidentally turned on when the laser diode is replaced by a short? Ideally, it will regulate the current anyway and not cause any problems, but how can I be sure? Do you have any solution to this problem (e.g. short diode with low value resistor rather than direct short)? I am interested to hear your ideas.

Best regards,

weartronics

[mixedgas]

But, what happens if the power supply is accidentally turned on when the laser diode is replaced by a short? Ideally, it will regulate the current anyway and not cause any problems, but how can I be sure? Do you have any solution to this problem (e.g. short diode with low value resistor rather than direct short)? I am interested to hear your ideas.

Best regards,

weartronics[/QUOTE]

Since Lasorb , to the best of my knowledge, are not yet available in Q1, the best bet is a relay right up against the diode in the housing. I'm basing this on Mr Benner's frequent statements that small loops bigger then a inch or so make a diode very vunerable to ESD instead of protecting it.

Keep the relay spikes off the diode supply PSU, ie use a seperate supply and make sure you have a snubber cap AND a power schottkey diode across the relay coil.

A diode is what equal to 2-3 ohms? Its gonna be hard to find a 1-2 ohm non inductive 5 watt resistor to put in series with the relay contacts, so I'd just put pure relay across the diode.
read the tutorial at
http://www.lasorb.com/

I'd hope your average psu designer made it tough enough to take a short for small periods of time.

Steve

[Pangolin]

Hi,

Steve is right. First, any ESD protection scheme has got to be closer than 5cm (round trip -- in a practical sense this means 2.5cm with two leads) away from the laser diode. See the PowerPoint here:
http://www.pangolin.com/_Files/LASORB.pdf

Second, as we tested a lot of different ESD protection schemes, we fell out of love with relays. With the exception of RF reed relays, normally there is a relatively long length that the connection goes through within the frame of a relay. This long length can be close to other components (such as the relay coil) and ESD can induce voltage into those components, possibly making the effects of ESD even worst.

Third, you must remember that 15kV ESD (rather common) is equivalent to a 50 amp pulse! In order to protect the laser diode from this, the protection sceme needs to be less than 50 milli-ohms impedance from around 20MHz all the way past 1GHz!

Before we started the LASORB project, I figured a relay was the perfect tool. But once we really began studying this, I now think that a relay is not such a good idea.

We are pretty close to releasing LASORB. The only thing left to work out is the "packaging". In our opinion, the best way to protect a laser diode is to install a LASORB device directly inside the laser head, as close as possible to the laser diode.

Bill

[weartronics]

Hi Steve and Bill,

LASORB looks like a great product, thanks for bringing it to my attention. I especially liked the testing with a tesla coil . Lots of relevant information on that site. Since this is a one-off installation which needs to be done this year and LASORB isn't available yet, I will use a relay with the shortest leads possible.

Best regards,

weartronics

[mixedgas]

hey Bill, since Lasorb (tm) switches so fast, any chance of using it as a step recovery diode for microwave frequency multiplication? My amateur radio hobby is 10 ghz microwave, as shortwave and two meters is very boring,

Steve Roberts

[ljk]

mixedgas,

It is nice to see that there is another ham on the board.

n7lxz

[mixedgas]

when I'm actually radiating, I'm N8VKD.

Steve

[Pangolin]

hey Bill, since Lasorb (tm) switches so fast, any chance of using it as a step recovery diode for microwave frequency multiplication? My amateur radio hobby is 10 ghz microwave, as shortwave and two meters is very boring,

Steve Roberts

Hi Steve,

LASORB really does one very specific thing -- eats ESD. It does it better than anything else we have seen anywhere. Laser Diodes are particularly suceptible to ESD because laser diodes (especially small ones) have reaction times in the GHz. This can theoretically react in somewhere between 200 and 800 picoseconds, so it is fast enough to protect a laser diode. It will work to protect an LED and other opto-electronic devices as well.

But for use as anything but an ESD protector, I would say it is pretty doubtful, and there has got to be a better device to do other jobs.

Bill