Stan_Ham diode driver (analog)

[Anthony]

But hey, if I must choose between wathing some foto's (pohotgraph or watching a lasershow, I know what I will choose. Watching photo's with friends give a much less oooohh aaaah effect .

Thats completely true.

But i don't make pictures for my friends to watch...
I don't make them for the ooh ahhhs... its a form of relaxment.
Going somewhere.. setting up/technical stuff and freezing just that moment of time or state.

Its hard to describe... but it is relaxing for me.

[djscsi]

Hello All,

Anthony, sorry to hear about your troubles, but we all understand there are often more important things in your life than these expensive hobbies. I am grateful for the design as it's helped me learn about laser drivers and electronic circuits in general.

Mcarrot:

I have built a couple of these driver boards and would be willing to try some new features, but I am new to circuit design so I would need some help testing. I am getting an oscilloscope soon but don't fully understand how to use everything. I imagine it will be necessary to safely test the modifications to the driver without risking blowing up lasers.

Anthony, are you and Rob OK with us making some modifications to the drivers and releasing the schematics/layout here?

One modification I will be making on the next board is a header for external dimming pot. This is so you can set the laser max-power with the main pot, then connect an external potentiometer (on the projector case for instance) for temporary dimming of the laser without affecting the max power level adjustment. This will be useful for testing (tuning, alignment, etc) at reduced power level without affecting the max laser power output. When not in use, this header can be covered with a jumper to operate normally.

I am also planning to lay out a dual-driver board with a LM324 (quad opamp) as it should not increase the size of the finished board very much. I think some people may be interested in this for running red/violet diodes off one board.

I am open to any ideas. I don't want to "take over" the project since I'm a newbie, but the driver has been working well for me and I would like to see other people enjoy it as well!

I would also be happy to post a parts list from mouser.com if anyone is not sure about which parts to use. The total parts list (not including pcb and etching/drilling materials) is under $5 even if parts are ordered individually, and Mouser is happy to ship small orders such as this.

One question I have is about the 1ohm resistor - is this just for measuring output current by watching the voltage drop across the resistor, or does it serve some other function in the circuit?

[mccarrot]

Wat I would like to see in your "new" design is more protection for the lasers diodes.

Many of us allready killed some (or allot ) laser diodes becouse of simple diode drivers.

I would like to see a softstart (you can copy this circuit from the Die4Drive schematic) to prevent voltage peak from the PSU when powering up kills the diode.

Also I would like to see some kind of ESD protection, like a transorb and/or varistor protecting the diode. (I can provide you the transorbs for the prototype)

Also I would like to see some kind of overvoltage protection the prevent a crazy PSU to kill the laserdiode. You could think of a 5,1V zener diode over the 5V rail.


Unfortunally this probbably will be a all theorie project becouse I don't think any of us is willing to kill allot of diodes to find out wat really works like Bill Benner (pangolin) allready did.

[djscsi]

I would like to see a softstart (you can copy this circuit from the Die4Drive schematic) to prevent voltage peak from the PSU when powering up kills the diode.

I am looking at the "soft start" part of the circuit and it looks like its just a very small capacitor between ground and the op-amp + input. It is jumpered to ground to enable soft start. I guess this is just smoothing for quick changes in drive current but I'm not totally sure. I guess I could ask the designer of the die4drive circuit I am in over my head here. My concern was that soft-start would affect blanking/modulation response time but this will need to be tested on an oscilloscope to see what happens.

Also I would like to see some kind of ESD protection, like a transorb and/or varistor protecting the diode. (I can provide you the transorbs for the prototype)

I have never used a transorb but I will look into it (again I am new to circuits so this will take me awhile). If I can find one in DO-15 or other through-hole type package (not doing SMD at this point) then I can try incorporating it into the circuit. Am I looking for a suppressor which has a breakdown voltage around 5-6v? This seems to be the bottom end spec for breakdown voltage on TVS, at least in this package. Some help here would be useful.

Also I would like to see some kind of overvoltage protection the prevent a crazy PSU to kill the laserdiode. You could think of a 5,1V zener diode over the 5V rail.

I don't see this in the die4drive schematic but 5.1v may have to be inline with the laser diode output as the driver circuit wants +6v input so it has enough voltage for a BR diode after the voltage drop of various diodes / transistor / etc.

Edit: I should add that for this circuit I am using a simple regulated +6V power supply made from a 7806, so I expect the voltage regulator will absorb excess input voltage and will be the component that fails in case of input voltage surge. Could also use a LM317 here but I was ordering parts so the 7806 seemed appropriate.

If someone more versed in circuit design wants to help, I can do some testing for the community, but cannot guarantee how fast I can get the work done since I'm still learning! Please let me know if I have misunderstood anything.

cheers,
Justin

[Pangolin]

Also I would like to see some kind of ESD protection, like a transorb and/or varistor protecting the diode.

Hehe. Speaking from experience, I can tell you that neither of these will work for a laser diode. We tried both. Both makes perfect sense but neither work.

Lucent Technologies even patented the use of a multi-layer varistor for the prupose of protecting a laser diode from ESD. Unfortunately, ultimately it doesn't work either... Even in Lucent's own charts in their patent, they showed that all laser diodes eventually died...

Unfortunally this probbably will be a all theorie project becouse I don't think any of us is willing to kill allot of diodes to find out wat really works like Bill Benner (pangolin) allready did.

Hehe. Yes, we killed a lot of diodes trying to determine what works and what doesn't. In fact, even tonight I killed fourteen 5mW red diodes just to see if I can make a specialized capacitor work as well as LASORB. (it won't...)

So yes, we know what works and what doesn't from experience.

LASORB will soon be available and will probably be nearly as inexpensive as a good multi-layer varistor anyway... Plus it provides other benefits such as reverse bias (aka reverse polarity) protection.


Bill

[allthatwhichis]

But you can't fix stupid...

[helium]

Hmmm, how about a Pangolin Lasorb Brain Implant? Anyone available for testing out there?

[Pangolin]

But you can't fix stupid...

True. And according to Jesse Ventura, can't legislate against it either...

Bill

[mccarrot]

Hehe. Speaking from experience, I can tell you that neither of these will work for a laser diode. We tried both. Both makes perfect sense but neither work.

Lucent Technologies even patented the use of a multi-layer varistor for the prupose of protecting a laser diode from ESD. Unfortunately, ultimately it doesn't work either... Even in Lucent's own charts in their patent, they showed that all laser diodes eventually died...


Bill

I don’t know if it coincidence but since I put tranzorbs on the input of my driver and over the laser diode I didn't had a failing diode since.

[b52productions]

i checked the website but i cant buy lasorbs there. so whats the deal bill?