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ArcticMyst Security by Avery

What happened here? (DDL Circuit problem)

Joined
Mar 15, 2009
Messages
74
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8
So I recently built a LM317 circuit. So I was watching a video and well calculated that to get the required output current I built this.

fego74.jpg


Well the output was expected to be around 50mA and before setting it up to the diode it ran as expected.

So what we did (we as in my friend and I) discharged the capacitor and hooked it up to the laser diode. We ran the diode on 5v and it was dim. Guessing that it was too weak to run on 5v we hooked it up to a 12v power supply and nothing happened. So we then checked the output after removing the laser diode and we were getting 30v out! we had no amps coming out and well I'm guessing that the laser got fried, but yeah. I don't know. Anyone want to help me out?
 





Blord

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The green line behind 30 Ohm must not connect and the 2 dots above the 1N4004 must be connected.
Correct me if I am wrong.


This is the correct diagram.
LM317%20components01.jpg
 
Last edited:
Joined
Nov 10, 2008
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So I recently built a LM317 circuit. So I was watching a video and well calculated that to get the required output current I built this.

fego74.jpg


Well the output was expected to be around 50mA and before setting it up to the diode it ran as expected.

So what we did (we as in my friend and I) discharged the capacitor and hooked it up to the laser diode. We ran the diode on 5v and it was dim. Guessing that it was too weak to run on 5v we hooked it up to a 12v power supply and nothing happened. So we then checked the output after removing the laser diode and we were getting 30v out! we had no amps coming out and well I'm guessing that the laser got fried, but yeah. I don't know. Anyone want to help me out?

Your circuit is a bit complicated.. Try to build the driver on a protoboard first, to make sure it is working properly. Then solder all parts together to get the driver done. There's only one tip: Make sure all the connections are correct and when you connect all components, use a light bulb or LED to test the driver, by turning the potentiometer both ways.
 
Joined
Feb 5, 2008
Messages
6,252
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Silvershot, there is no potenciometer. There's only a 30 ohm fixed ressitor.

1.25 Vref / 30 ohms = 0,041 A = 41 mA. Is that correct?

What diode are you working with here?

It says "4XLD" So I'm guessing it's a red laser diode from 4x DVD burner.

If I am not mistaking, 40 mA is below lasing threshold. You have not given it enough joice. Don't bother with 30V reading, it's incorrectly measured. It was not fed to your laser diode.

Ram the current up to 100mA. Then see what happens. You'll need a 12 ohm resistor for that.

Never measure the output voltage. Just make sure your INPUT voltage is at least 2.5 V greater than needed output, which is around 3 V for reddies, so you need at least 5.5 V (6V reccomended) input voltage requirement.
 
Joined
Mar 15, 2009
Messages
74
Points
8
Silvershot, there is no potenciometer. There's only a 30 ohm fixed ressitor.

1.25 Vref / 30 ohms = 0,041 A = 41 mA. Is that correct?

What diode are you working with here?

It says "4XLD" So I'm guessing it's a red laser diode from 4x DVD burner.

If I am not mistaking, 40 mA is below lasing threshold. You have not given it enough joice. Don't bother with 30V reading, it's incorrectly measured. It was not fed to your laser diode.

Ram the current up to 100mA. Then see what happens. You'll need a 12 ohm resistor for that.

Never measure the output voltage. Just make sure your INPUT voltage is at least 2.5 V greater than needed output, which is around 3 V for reddies, so you need at least 5.5 V (6V reccomended) input voltage requirement.

Okay, but this is exactly what I needed to see. Some actual math. The only question that remains is when my friend wired the laser directly to 2 AAA batteries to see if it lit up and it did. We only did so for a moment. When we fired up the laser with the driver it did nothing so we tested it with the 2 AAA's again and it did nothing.
 
Joined
Feb 5, 2008
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Live and learn, my friend :)

Congratulations, you have learned the hard way why direct driving of diodes is bad idea.
It's the direct connection to batteries that has destroyed your diode, not the driver.

Driver is essential. You need it. If diodes worked without it, we would use them without it.

Anyhow, time to order new diode I think. Take a look here:
HighTechDealZ - Lasers

Also, would you please take picture of your driver so we can prevent any possible problems that might arrise with new diode?


About the math, calculate needed current with this:
1.25 [Voltage refference] / desired current in A [Not mA!] = resistance in Ohms

For red diode's current, 100mA is good starter current to see if it works.
When you know that the type of the diodei s long emitter one, ramp up to 400mA no problem. However, if short emitter die, might not survive over 300mA.
 
Joined
Feb 5, 2008
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No, you have wired it wrong, mister Blord. Take care where is Output and Adjustable on that schematic representation of LM317, little box has, from left to right :
Input, adj, out,
While real one would have:
Adj, out, input .

So basically, except it being turned the other way around, has ADJ and OUT reversed too, and you got yourself confused by it.

Besides, don't you think that the attached schematic would be the first place I would search for error prior to replying to the thread? ;)

His schematic is alright as far as I can see. Bit complicated, I'd omit the rectifier diode, but it's OK.
 
Joined
Mar 15, 2009
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Sorry for the double post in advance. I really want to thank all of you guys here at LPF. It really really helps to have people help when I have no clue what I'm doing. I plan to build a PHR - 803T. I want to go all out with the laser in a proper housing (I'm talking about the laser module with lense mounted in something like a jayrob kit(?) I might not know what I'm talking about xD)
 
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Joined
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Well, the diode is so that the negative wont run in the positive line and break the diode.
Yeah but that's only in the case you reverse the battery input, which is pretty tough in labby build (not so unlikely in handheld built but still),

About your PHR build.

You need to know what host you want to use. We'll move on from there.

My warm reccomendation would be Cree C6, Jayrob here sells a kit with heatsink premade for it and with driver pill with contact board for battery contact.
 




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