Killed 2 LOC diodes last night, don't know why...

comradmax · Oct 12, 2010

Well, I am up to 5 dead diodes now in my quest to learn how to build lasers... I appologize in advance for the long post, but I would greatly appreciate any help in troubleshooting my mistakes.

Connected LOC #1, turn on, very dim TEM02 dot. Took the head off, connected DMM in series with LD, turn on: ~50mA... LD must have died right away

Harvested LOC #2, turn the pot down to 30mA, short Vout and GND. Connect the new LD, turn on, very dim TEM02 dot. Open, using test-load set pot to 150mA, short Vout-GND, plug in LD - slightly brighter dot. Take apart, set to 300mA, short Vout-GND, plug in LD - very bright dot for 1sec, then dim, and also dead

I fried my last 2 LOC diodes yesterday

I am trying to build inside a flashlight host. I made a linear driver using LD1117 chip, schematic is attached below. I used 2 freshly charged Li-Ion 10440 cells, using the 3xAAA pill from the host and bridging one of the slots with a bolt+nut, the pill read 8.35V. The host's switch sits between the battery + and the driver, host is case negative.

LD and head
Using a 4x diode test-load I set the current to 420mA. Shorted Vout and GND, double-checked with DMM - ~1-3mV, so I figured it's safe to connect the LD. LD is pressed in Aixiz, + and - soldered to Flaminpyro's wire. Aixiz inserted in a big heatsink I bough from Matt before, heatsink inserted into flashlight head and made stable with O-rings. The heatsink and host are electrically isolated via the rubber o-rings. GND from LD soldered to the inside of the head, + wire soldered to a spring. The spring is attached to the bottom of the Aixiz/Heatsink, the idea is that it will make contact with the Vout on the host tube. This spring is isolated from the heatsink, I made a "disk" spiral from insulated wire that sits between the spring and the heatsink.

Vout
One of the pictures shows my Vout contact point for the spring: I soldered a wire to Vout from the driver, then made a round "bowl" from a catfood can and soldered the other end to that.

Harvesting
Cut the ribon wire, poped the LD+heatsink from the sled with a screwdriver. Using the "blob of solder" method I quickly removed the ribbon. Filed a V into the sides of the heatsink alsmost to the diode itself. Using pliers and the screwdriver I cracked the heatsink and the diode came out easily. I used a motherboard standoff and tonge-and-groove pliers to carefully press the diode into Aixiz. Soldered lead wires to +/-, this was very quick and made a nice shiny connection with both the wire and the pin envelopped in solder. I put heatshrink on it and used a blowdryer.

ESD
I have no metal pipes in my apt, so I would touch the metal frame on the table each time before touching the diode. I wore no socks and my floors are hard wood. My soldering iron has 3 prongs, but that may not necessarily mean it's grounded.

I now have no more laser diodes left to try

I don't understand how I killed them or what I did wrong. The way LOC #2 died suggest to me it was capable of some lasing, but 300mA was too much current for it. This makes little sense, LOC's take 400mA+ all the time I thought... I did not have an input capacitor due to space limitations, but I'm using batteries, so I figured they wouldn't spike. Besides I have a 10uF output cap. Was it ESD during the build process that caused this?

Eudaimonium · Oct 12, 2010

Here we go again, schematic of NON-BENCH power supply with F'cking potenciometer.

Thanks a lot to whoever suggested using potenciometers in DIY drivers. I fried my first 20 red diodes blindly following the stupid potenciometer design.

Here's a proper schematic.

LM317 and LM1117 are connected in exactly the same way, so disregard the label.

Use formula to calculate needed resistor.

You can use 3.3 ohms for 380mA or 3 ohms for 415 mA, whichever you got handy.
Just solder up and have fun. Forget trimming and test loading.

I'll refrain from hugeass post of ranting about freaking pots.

EDIT - Addendum
From all the ranting I forgot about actual info and tips.

First, make sure you are not connecting the diode directly to batteries, I mean, measure resistance between positive input and positive output of your driver. It should not be short circuit. If it is, it means you shorted something.

Next, you can throw out a freaking capacitor out of that schematic. They killed more diodes than they actually saved anyhow. Optional.

Finally, your LM chip might as well be faulty. Re-check that.

I do place my bet on the resistance on Vref though. You are most likely shorting resistors out, or potenciometer is not reliable.
Simply use one fixed resistance.

It's not a bench supply that it requires adjustable power output, and it's not a bulk driver design like DrLava drivers, that you will sell.

bootleg2go · Oct 12, 2010

comradmax said:
Well, I am up to 5 dead diodes now in my quest to learn how to build lasers... I appologize in advance for the long post, but I would greatly appreciate any help in troubleshooting my mistakes.

Connected LOC #1, turn on, very dim TEM02 dot. Took the head off, connected DMM in series with LD, turn on: ~50mA... LD must have died right away

Harvested LOC #2, turn the pot down to 30mA, short Vout and GND. Connect the new LD, turn on, very dim TEM02 dot. Open, using test-load set pot to 150mA, short Vout-GND, plug in LD - slightly brighter dot. Take apart, set to 300mA, short Vout-GND, plug in LD - very bright dot for 1sec, then dim, and also dead

I fried my last 2 LOC diodes yesterday I am trying to build inside a flashlight host. I made a linear driver using LD1117 chip, schematic is attached below. I used 2 freshly charged Li-Ion 10440 cells, using the 3xAAA pill from the host and bridging one of the slots with a bolt+nut, the pill read 8.35V. The host's switch sits between the battery + and the driver, host is case negative.

LD and head
Using a 4x diode test-load I set the current to 420mA. Shorted Vout and GND, double-checked with DMM - ~1-3mV, so I figured it's safe to connect the LD. LD is pressed in Aixiz, + and - soldered to Flaminpyro's wire. Aixiz inserted in a big heatsink I bough from Matt before, heatsink inserted into flashlight head and made stable with O-rings. The heatsink and host are electrically isolated via the rubber o-rings. GND from LD soldered to the inside of the head, + wire soldered to a spring. The spring is attached to the bottom of the Aixiz/Heatsink, the idea is that it will make contact with the Vout on the host tube. This spring is isolated from the heatsink, I made a "disk" spiral from insulated wire that sits between the spring and the heatsink.

Vout
One of the pictures shows my Vout contact point for the spring: I soldered a wire to Vout from the driver, then made a round "bowl" from a catfood can and soldered the other end to that.

Harvesting
Cut the ribon wire, poped the LD+heatsink from the sled with a screwdriver. Using the "blob of solder" method I quickly removed the ribbon. Filed a V into the sides of the heatsink alsmost to the diode itself. Using pliers and the screwdriver I cracked the heatsink and the diode came out easily. I used a motherboard standoff and tonge-and-groove pliers to carefully press the diode into Aixiz. Soldered lead wires to +/-, this was very quick and made a nice shiny connection with both the wire and the pin envelopped in solder. I put heatshrink on it and used a blowdryer.

ESD
I have no metal pipes in my apt, so I would touch the metal frame on the table each time before touching the diode. I wore no socks and my floors are hard wood. My soldering iron has 3 prongs, but that may not necessarily mean it's grounded.

I now have no more laser diodes left to try I don't understand how I killed them or what I did wrong. The way LOC #2 died suggest to me it was capable of some lasing, but 300mA was too much current for it. This makes little sense, LOC's take 400mA+ all the time I thought... I did not have an input capacitor due to space limitations, but I'm using batteries, so I figured they wouldn't spike. Besides I have a 10uF output cap. Was it ESD during the build process that caused this?

Hi comrad,
The problem is not at all related to the circuit or having a pot. A pot will not hurt at all as long as there are other current limiting resistors in series, which your schematic shows.
The problem is entirely ESD related.
What worries me the most is that you mentioned your soldering iron has 3 prongs.... Does that mean it's plugged directly into the wall power outlet?
If so, that is the most likely cause right there. You need an iron that is isolated for ESD sensitive components; which means a little higher quality iron with it's own power transformer and not an iron that plugs directly into the wall.
That will get you 1/2 way there, you still need to have an ESD protected workplace; just taking your socks off and touching a metal surface won't do it.
1. get or borrow a wall outlet power tester to determine if the wall outlet is even wired correctly and properly grounded. Just because your outlet will power a device, doesn't mean it's wired correctly or properly grounded. When I was an engineer at Maxtor I was once blowing parts left and right and then found out that there was almost 40vac on my workbench because my bench was no longer grounded correctly.
After you check this and get it fixed if needed, you will then have a real ground on one of the prongs of your wall outlet. Connect this ground to your workbench. If the bench is metal, then connect directly to the bench. If it's not, then you will need an ESD mat for the surface and connect ground to the mat. You will also need an ESD wriststrap that also is connected to the mat or metal workbench and then put it on before touching the parts and doing your work.

While you have the outlet checker, check every outlet in the house to make sure they are all wired correctly. If one is wrong, then other probably are too and it can be deadly under the right conditions.

Eudaimonium · Oct 12, 2010

bootleg2go said:
Hi comrad,
The problem is not at all related to the circuit or having a pot. A pot will not hurt at all as long as there are other current limiting resistors in series, which your schematic shows.
The problem is entirely ESD related....

I beg to differ.

With all the point to point soldering there, adding components which are totally unnecessary makes so much room for error that there practically is no point in making it.

Why would you put a pot there?
What's the porpose?

You say "as long as there's current limiting resistor..." - exactly! Why the hell do you need that pot for ?

It's totally unnecesary in this case.

Morgan · Oct 12, 2010

I would also say that ESD would have killed an LD stone dead. Not allowed it to lase broghtly for a second before death as in the case of LOC #2 there. COD from optics? Doubtful at 300mA but a consideration.

Also, extraction, although sometimes it could appear easy is often a killer. One tiny slip and the die is damaged. Do you have any pics of the original heatsinks?

Are you also sure, OP, that LOC #1 is actually dead? From your post it seems you only ran it at ~50mA? That'd barely be above threshold wouldn't it?

M

bootleg2go · Oct 12, 2010

Eudaimonium said:
I beg to differ.

With all the point to point soldering there, adding components which are totally unnecessary makes so much room for error that there practically is no point in making it.

Why would you put a pot there?
What's the porpose?

You say "as long as there's current limiting resistor..." - exactly! Why the hell do you need that pot for ?

It's totally unnecesary in this case.

Hi Eudaimonium,

You would have one to control output, just lkie a laser system uses a pot to control it power.
Where did you get your electrical engineering degree?
Mine is from the Denver Institute of technology and then from the Unversity of Colorado and have been designing circuit since before a majority of the LPF members were even born.
Not to mean any disrespect, as I don't know you very well and I've seen a lot of posts in the LPF the year or two from kids as well as adults without any college degree in electronics giving out electronics design advice with little or no educational background to backup their advice.

If you have your EE degree, it should be obvious as to why the pot would be in this circuit, of course if no fine adjust of power is needed or wanted you could do without, but since most off the shelf resistors are only 10% tolerance, the final desired power applied would only be 10% as well unless either the time were taken to verify exact resistor values or a pot used to fine tune.
Either way, having a pot in the circuit will not cause any harm.

Eudaimonium · Oct 12, 2010

bootleg2go said:
Hi Eudaimonium,

You would have one to control output, just lkie a laser system uses a pot to control it power.
Where did you get your electrical engineering degree?
Mine is from the Denver Institute of technology and then from the Unversity of Colorado and have been designing circuit since before a majority of the LPF members were even born.
Not to mean any disrespect, as I don't know you very well and I've seen a lot of posts in the LPF the year or two from kids as well as adults without any college degree in electronics giving out electronics design advice with little or no educational background to backup their advice.

If you have your EE degree, it should be obvious as to why the pot would be in this circuit, of course if no fine adjust of power is needed or wanted you could do without, but since most off the shelf resistors are only 10% tolerance, the final desired power applied would only be 10% as well unless either the time were taken to verify exact resistor values or a pot used to fine tune.
Either way, having a pot in the circuit will not cause any harm.

Kind of hard to make out the sarcasm from actual coversation here, but I'll go with the asumtion that all these are actual questions.

I do not have EE degree, I am a first year student of Fakultet Organizacije i Informatike college in Varaždin in Croatia (that means as much to you as places where you got your degrees mean to me).

EE degree however, is not needed for one to understand electronical circuitry.
It's also not needed to evaluate if a potenciometer is needed in starter DIY laser build.

And the concluding answer, no, we do not want actual precision control, because trimming your laser to a mA, which turns into trimming it into precise that one mW of output, is not exactly worth risking a diode over it. Or five.

I see no logic in putting potenciometer there. Takes space, complicates things, and after laser is built, just kind of sits there.

And no, it's not 10%, it's 5% tolerance, as indicated by little gold color ring, for standard readily available resistors.
As far as resistors available to me go, that is.

bootleg2go · Oct 12, 2010

Eudaimonium said:
Kind of hard to make out the sarcasm from actual coversation here, but I'll go with the asumtion that all these are actual questions.

I do not have EE degree, I am a first year student of Fakultet Organizacije i Informatike college in Varaždin in Croatia (that means as much to you as places where you got your degrees mean to me).

EE degree however, is not needed for one to understand electronical circuitry.
It's also not needed to evaluate if a potenciometer is needed in starter DIY laser build.

And the concluding answer, no, we do not want actual precision control, because trimming your laser to a mA, which turns into trimming it into precise that one mW of output, is not exactly worth risking a diode over it. Or five.

I see no logic in putting potenciometer there. Takes space, complicates things, and after laser is built, just kind of sits there.

And no, it's not 10%, it's 5% tolerance, as indicated by little gold color ring, for standard readily available resistors.
As far as resistors available to me go, that is.

None of my reply was sarcasm; just electronics design information and my opinion that sometimes advice is given here on the forum with no or little educational background needed to give good adive on the subject at hand.
This does not apply to you, you're the expert here as I see you have thousands of posts more than I.
You're right when you said
"EE degree however, is not needed for one to understand electronical circuitry"
(now that was my sarcasm for the day)
And the fact that I got those degrees almost 10 years before you were even born only means my information is old, outdated and no longer valid.

Yes adding the pot does complicate it a little, but pots are about as simple a component as there is. Yes, it also takes up space.
The OP could if he chooses, use a pot, then when it's set to it's best value, solder in a resistor of that value and have the best both worlds.

I didn't read when the OP said the tolerance of his resistors, I was just going by what is the most common value sold in electronic retail outlets here in the states and those are usually 10% or or worse.

Bottom line is the OP needs to get his ESD porblem taken care as that's his problem here.

I'm Sorry that I wrongly posted in this thread and tried to suggest that my electronics background and nearly 30 years of experience in electronics and circuit design surpassed yours in any way: it won't happen again.

Eudaimonium · Oct 12, 2010

bootleg2go said:
None of my reply was sarcasm; just electronics design information and my opinion that sometimes advice is given here on the forum with no or little educational background needed to give good adive on the subject at hand.
This does not apply to you, you're the expert here as I see you have thousands of posts more than I.
You're right when you said
"EE degree however, is not needed for one to understand electronical circuitry"
(now that was my sarcasm for the day)
And the fact that I got those degrees almost 10 years before you were even born only means my information is old, outdated and no longer valid.

Yes adding the pot does complicate it a little, but pots are about as simple a component as there is. Yes, it also takes up space.
The OP could if he chooses, use a pot, then when it's set to it's best value, solder in a resistor of that value and have the best both worlds.

I didn't read when the OP said the tolerance of his resistors, I was just going by what is the most common value sold in electronic retail outlets here in the states and those are usually 10% or or worse.

Bottom line is the OP needs to get his ESD porblem taken care as that's his problem here.

I'm Sorry that I wrongly posted in this thread and tried to suggest that my electronics background and nearly 30 years of experience in electronics and circuit design surpassed yours in any way: it won't happen again.

Yeah that entire post was like... definetly sarcastic.

EE degree is not needed to understand *this level* of electronics.

We all know post count means nothing.

It's obvious that a man with EE degree knows more than I will ever know, I admit that and we know it.

It's highlighted part that worries me. I did not manage to even find any 10% tolerance resistors for sale locally. Cheapest ones are always 5%, and beefy 5W and above are either 2% or less. Well that is half a globe apart, but your half is the better one.

comradmax · Oct 12, 2010

First off, I'd like to thank everyone taking their time to read this and provide help

I also spoke with Eudaimonium on #laserchat and ordered LPC+PHR sleds from hightechdealz.com as suggested, so at least i'll be able to try again sooner than that GB goes through...

I think my best course of action should be to put the flashlight host builds on hold and make some "labbies" first. I will make PCB's and use set components, not pots, to minimize the risk. Technically I don't need the pot as I'd want the laser to run at max anyway...

Eudaimonium said:
You can use 3.3 ohms for 380mA or 3 ohms for 415 mA, whichever you got handy.

Next, you can throw out a freaking capacitor out of that schematic. They killed more diodes than they actually saved anyhow. Optional.

Finally, your LM chip might as well be faulty. Re-check that.

I found that 3.3 Ohm would produce 420mA with my setup. This does not agree with the standard 1.25/R=I formula, most likely due to something I did wrong during testing. I will also try a fresh LD1117 chip. I am all for throwing out the other parts and leaving just the chip and a resistor, would anyone else like chime in on how necessary any of the other components are?

bootleg2go said:
A pot will not hurt at all as long as there are other current limiting resistors in series, which your schematic shows.

What worries me the most is that you mentioned your soldering iron has 3 prongs.... Does that mean it's plugged directly into the wall power outlet?

If it's not, then you will need an ESD mat for the surface and connect ground to the mat. You will also need an ESD wriststrap that also is connected to the mat or metal workbench and then put it on before touching the parts and doing your work.

While you have the outlet checker, check every outlet in the house to make sure they are all wired correctly.

The thing is that those current limiting resistors add up to 2.5Ohm, which I chose to give me a "nice range" with the 100Ohm pot - this resistance alone would most likely blow my diode as the current will be 500mA. So I did not make a very safe circuit, if something did short that pot

My soldering iron is a "station" type, the station plugs into the outlet via 3 prongs and has a knob to set temperature. It's not a Weller, but it did cost me ~$50 if i remember correctly. I do have an outlet checker with 3 lights, I will test my apt to see if the GND is even connected. My table top is not metal, so I will do some research into these ESD mats, I wasnt aware of them, so thanx!

Morgan said:
I would also say that ESD would have killed an LD stone dead. Not allowed it to lase broghtly for a second before death as in the case of LOC #2 there.

Also, extraction, although sometimes it could appear easy is often a killer. One tiny slip and the die is damaged. Do you have any pics of the original heatsinks?

Are you also sure, OP, that LOC #1 is actually dead? From your post it seems you only ran it at ~50mA? That'd barely be above threshold wouldn't it?

I've read on the forum that if ESD kills a diode, then it's dead from the start, like you just said (remember that 'plexus' fiasco?). I didn't take pictures of the extraction, this is prolly a good idea to do on my next try. LOC #1 was powered on at 420mA, sorry for the confusing post: I set the driver to 420mA originally, connected and killed LOC #1, then I panicked and turned it down before plugging in LOC #2.

bootleg2go said:
as to why the pot would be in this circuit, of course if no fine adjust of power is needed or wanted you could do without, but since most off the shelf resistors are only 10% tolerance, the final desired power applied would only be 10% as well unless either the time were taken to verify exact resistor values or a pot used to fine tune.

I used these resistors, they are 1%. I did use the pot to be able to dial in exactly 420mA, as that would require either a single reistors of a value I did not have or too many 1 Ohm reistors to make the 0.3

Here is the pot that I used.

So, the moral of this story is: a) spend a lot more time understanding ESD and getting a proper work-space setup, b) KISS and start even slower than I have to get some more experience with lasers

Thanks again for people taking their time to help me, a noob.:beer::beer::bowdown:

bootleg2go · Oct 13, 2010

comradmax said:
First off, I'd like to thank everyone taking their time to read this and provide help I also spoke with Eudaimonium on #laserchat and ordered LPC+PHR sleds from hightechdealz.com as suggested, so at least i'll be able to try again sooner than that GB goes through...

I think my best course of action should be to put the flashlight host builds on hold and make some "labbies" first. I will make PCB's and use set components, not pots, to minimize the risk. Technically I don't need the pot as I'd want the laser to run at max anyway...

I found that 3.3 Ohm would produce 420mA with my setup. This does not agree with the standard 1.25/R=I formula, most likely due to something I did wrong during testing. I will also try a fresh LD1117 chip. I am all for throwing out the other parts and leaving just the chip and a resistor, would anyone else like chime in on how necessary any of the other components are?

The thing is that those current limiting resistors add up to 2.5Ohm, which I chose to give me a "nice range" with the 100Ohm pot - this resistance alone would most likely blow my diode as the current will be 500mA. So I did not make a very safe circuit, if something did short that pot My soldering iron is a "station" type, the station plugs into the outlet via 3 prongs and has a knob to set temperature. It's not a Weller, but it did cost me ~$50 if i remember correctly. I do have an outlet checker with 3 lights, I will test my apt to see if the GND is even connected. My table top is not metal, so I will do some research into these ESD mats, I wasnt aware of them, so thanx!

I've read on the forum that if ESD kills a diode, then it's dead from the start, like you just said (remember that 'plexus' fiasco?). I didn't take pictures of the extraction, this is prolly a good idea to do on my next try. LOC #1 was powered on at 420mA, sorry for the confusing post: I set the driver to 420mA originally, connected and killed LOC #1, then I panicked and turned it down before plugging in LOC #2.

I used these resistors, they are 1%. I did use the pot to be able to dial in exactly 420mA, as that would require either a single reistors of a value I did not have or too many 1 Ohm reistors to make the 0.3 Here is the pot that I used.

So, the moral of this story is: a) spend a lot more time understanding ESD and getting a proper work-space setup, b) KISS and start even slower than I have to get some more experience with lasers

Thanks again for people taking their time to help me, a noob.:beer::beer::bowdown:

Hi Comrad,
ESD is not an all or nothing kind of failure like you said you read.
It can be catastrophic and kill the component outright, or it can weaken it so that a lessor 2nd or 3rd ESD event could take it out. When I say weaken it I mean it might not show any sign of damage so you might think it's still just fine or it could damage it enough to affect it's performance, so for instance only work at partial power or have strange beam characteristics.

Yes, getting the wall outlet tester is the best place to start, they can be had online for less than $12 or so and some hardware stores might even let you borrow one.
Once you know that the grounding on the AC outlet is good and if you have access to a volt/ohm meter. Set the meter to measure AC voltage and put one of the probes into the ground plug, then plug your soldering iron into the plug above/below it and turn it on. Then before it gets too hot, measure the AC voltage between the ground plug and the tip of the soldering iron. Then do this with the meter set to DC. If either is more than 1V AC or DC, then there is a problem, most likely in the solder station.
This is more common than you think as ground loops are easy to make. I found out that hard way one time when the probe of my o-scope actually was actually a source for voltage because of this.

If you measure a voltage when doing this ge ton of those adapter plugs that changes a 3 prong device to a 2 prong device with a ground wire. Just let the wire hang and thus convert the solder station to a 2 prong device. This will often fix it as it will isolate the ground of the AC device from the AC source thus removing the ground loop and fixing the problem. What I've talked about here is not really ESD, but a voltage where none should be, which can and will damage the component just as easily.

It may sound boring and tedious, but you only need to do this once as long as grounding or tools don't change; then after your ESD safe work area is complete using wrist strap, you will never ESD damage a device again.
Oh, one more thing, your chair should be well grounded too. Best to use a metal one of course; but I think if you can get the workarea ESD proofed and use a wrist strap, you'll be 99% there and safe for working with laser diodes. Some FETs on the hand take it to another level of needed ESD protection.

As for the other components I would leave the capacitors in if the circuit designer included them. They usually have a purpose. Don't use just any type of cap though, find out if it needs to be a tantalum or simple ceramic disc capacitor. These will usually help prevent transient voltage spikes and they are often used to prevent positive feedback / oscillations.

Vaporizer · Oct 13, 2010

comradmax, sorry to hear of your loss. I wouldn't toss the diodes before trying another 117. TEM02 doesnt sound to good though. Could you be mistaking the low output for it?
I made the LM317 driver just as you show with a pot (25ohm wire wound from Rat Shack) and have yet to kill a diode with it. I have a current limiting resistor of just under 3 ohms too. I made a test load and I have ran my LOC's from styros GB for up to 1 min adjusting the power with the pot. Not a single failure. Its fun to watch it go from a low mw up to 467ma input. My son and I target it with low ma and then crank it up to burn.
I have a 2 wall prong AC 15/30 watt iron from Rat Shack. Nothing special. You mention a metal frame on your table. I put a wood top on my work area so ESD has never bit me yet. I do always keep my forearm against the table before touching anything. Old habit.

Can you get a LM317 locally? I have some 117's I just received in 2 diff pkg styles for diff power builds vs host size.

I did blow one LOC due to not discharging the cap on the driver. My test load has a 2.2K draining resistor so that problem is now a thing of the past.

Hope a new driver shows the diodes ok. I used a 47mfd but many have used a 10mfd tantalum.

I have to agree that something is commonly wrong. I had the limiting resistor com loose from the center pin due to a quick tack and the diode just quit lasing. It was fine after resoldering the resistor.

lazeerer · Oct 13, 2010

comradmax said:
I found that 3.3 Ohm would produce 420mA with my setup. This does not agree with the standard 1.25/R=I formula, most likely due to something I did wrong during testing. I will also try a fresh LD1117 chip. I am all for throwing out the other parts and leaving just the chip and a resistor, would anyone else like chime in on how necessary any of the other components are?

:

Hey, Sorry to here you are having so much trouble with your build.

I Just posted a build today of my PHR Budget build >>HERE<< Using the LM317T chip in a flashlight host laser. Yet its not a detailed build but you can see the Schematics that i fallowed on there was set with a single resistor.

Its the exact same schematics as Eudaimonium post in post #2 and IMO all you need is the resistor.

Hope this helps your assurance.

Also heres a link to plug in the mA to get the right resistor to use.
http://www.reuk.co.uk/LM317-Current-Calculator.htm

A 3 ohm resitor will give you 420mA.

Bionic-Badger · Oct 13, 2010

Did I read correctly that you're using an LM1117, the adjustable version? The LM1117 has a drop-out of 1.2V, which means you're giving that laser diode 7.2V from your two 4.2V LiPo batteries. That's high even for a 405nm diode. A red laser diode only needs about 3.5V max at 420mA; they're actually rated to run at 2.5V, and max 3.0V. If you're using an LM317, the dropout is about 3V, which is still about 5.4V. Try to reduce the voltage you're providing the driver so that it doesn't need to drop so much at the output. If I recall, I was able to power a red using a single CR123A using a Rckstr driver that I believe has an LM1117.

Second, how is your diode heatsinked? I remember with my first few red diodes I had them just in that Aixiz module, and to my great delight I could see a nice red light from them. Unfortunately, it was short lived and burnt out from the heat. They really need to be in the heatsink ready to go before you power them up.

If you're concerned about ESD, take a paperclip, crush it so that it has two wires running parallel to each other and clip it to the diode leads to short them before you solder the system up. Once you're soldered, unclip those leads and you should be ready to go. I never had a problem with direct-to-wall soldering irons and ESD, even when working while sitting on the carpet. Where I did fry diodes was when I was measuring the output using an multimeter inline with the laser diode to measure the current. When I switched the meter's setting from the ammeter to off or vice-versa it caused some surge that killed the diode. Moral of the story: pre-program the current before you solder up and leave it.

comradmax · Oct 13, 2010

bootleg2go said:
It may sound boring and tedious, but you only need to do this once as long as grounding or tools don't change; then after your ESD safe work area is complete using wrist strap, you will never ESD damage a device again.

This is a great tip, I will test the soldering iron like you said. It's not too tedious, this is all part of the electronics hobby

I hope my apt is wired correctly... I know that I do get a flat 120VAC out of my outlet, tested that recently.

bootleg2go said:
As for the other components I would leave the capacitors in if the circuit designer included them.

Here is the thing, I just took the DDL circuit and used the LD1117 chip instead of LM317

I just read on the forum that the cap is there to prevent spikes, so I used one in my driver. It's an electrolytic type.

Vaporizer said:
I wouldn't toss the diodes before trying another 117.

I didn't think to try them with a new driver. I will re-test the LOC's that I think I burned out, maybe I'll get super lucky and they still work!

Vaporizer said:
Can you get a LM317 locally?

I have some LM317's at my disposal, I've made a DDL circuit a while back. I can also try the burned LD's with an LM317 chip instead of my LD1117 just to make sure.

Lazeerer said:
I Just posted a build today of my PHR Budget build >>HERE<< Using the LM317T chip in a flashlight host laser. Yet its not a detailed build but you can see the Schematics that i fallowed on there was set with a single resistor.

Yea, I saw that post, great job on the build! I also noted that you just used the chip and the current limiting resistor, which is what's suggested by Eudamonium. Thanks for the encouragement, it helps to see someone using a simplified driver and working

Bionic-Badger said:
The LM1117 has a drop-out of 1.2V, which means you're giving that laser diode 7.2V from your two 4.2V LiPo batteries.

Hmm, I thought I did this right, but perhaps not... I used a test-load with 4 diodes to simulate the voltage drop of a LOC. I must admit that I don't remember what the voltage drop across them was at 420mA, but here are some points that I wrote down: 60mA->2.765V, 150mA->3.1V, 500mA->3.25V. So if I understand linear drivers correctly, the voltage drop will be governed by the current I am pushing through the load. Meaning, voltage drop will go up as I increase the current, but it will be what it needs to be. So I don't think I'm actually giving 7.2, even though the drop for the LD1117 chip is low - I think it's somewhere ~3.2V (I have the LOC graph for this at home that I found on the forum). My battery supplies 8.4V, LD needs and takes 3.2V, LD1117 takes 1.0V - that leaves 8.4-3.2-1.0=4.2V for the chip to convert into heat. The heat will decrease as the batteries drain and loose voltage.

Bionic-Badger said:
Second, how is your diode heatsinked?

Yes, I have the diode in the full Aixiz module, and the module inside a long aluminum heatsink. Here is a link to what I'm using, I'm the guy that bought # 3,4,5,6,7.

Bionic-Badger said:
If you're concerned about ESD, take a paperclip, crush it so that it has two wires running parallel to each other and clip it to the diode leads to short them before you solder the system up.

Thanx, I'll short the pins next time I'm working with laser diodes!

Vaporizer · Oct 13, 2010

comradmax, I knew I remembered reading it, had to find it. It in Daedals original post #14.
http://laserpointerforums.com/f42/diy-homemade-laser-diode-driver-26339.html
You can use a regular LED to test the driver. He explains on page 1 that the voltage isn't a concern with his design. It is more heat to convert as more current is required.

Hope you lost the 1117 rather than the diodes. BB is correct on the rckstr driver. It uses the LM1117 and the dropout is 1.1v.

Killed 2 LOC diodes last night, don't know why...

comradmax

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