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Old 04-05-2017, 04:37 PM #1
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Default Problems driving new diodes - low glow only

I purchased a dozen blue TO-18 laser diodes:
1pc 405nm 5.6mm 5mw-20mw Violet/Blue Laser Diode TO-18 | eBay

I wired one up directly to a 18460 Lithium battery just for fun when I got it and things worked fine, but I wanted to adjust the output power so I bought a bunch of these drivers:

Adjustable current laser diode driver 80-500mA w/TTL blue board | eBay

I tried to do things the "right" way and busted out my multi meter and tested the output voltage, which was just over 5V with no load which seemed right to me. Then I tried measuring the mA but had a hard time getting it where I wanted it, the adjustment didn't seem to go over 1mA, but I have never measured mA before and so I don't know that I was doing it right.

That being said, I soldered the diode to it and with the potentiometer adjusted down, I could get the diode to glow just a little, but I couldn't get any major beam out of it. I tested the voltage again wondering if I had shorted something out, but still had the 5V I expected.

Should these 2 work together? According to my calculations I should be able to run it at 5V around 4mA, so I went back to look at the driver specs which listed 80mA as the low range, but that didn't seem right for the size, but it made me think maybe I had toasted the diode, so I tested it again on the battery with no driver and it worked great.

Any tips for a beginner?


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Old 04-05-2017, 04:48 PM #2
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Default Re: Problems driving new diodes - low glow only

Quote:
Originally Posted by ajhalls View Post
I purchased a dozen blue TO-18 laser diodes:
1pc 405nm 5.6mm 5mw-20mw Violet/Blue Laser Diode TO-18 | eBay


That listing doesn't seem to specify diode current... or much else?

I wired one up directly to a 18460 Lithium battery just for fun when I got it and things worked fine, but I wanted to adjust the output power so I bought a bunch of these drivers:

Terrible idea, laser diodes need a current regulated source. Although that one may have been OK seeing as the cell's voltage is lower than the LD max forward voltage for a lot of 405nm diodes.

Adjustable current laser diode driver 80-500mA w/TTL blue board | eBay

The minimum current on that driver may be higher than your LD can take safely. Hard to say seeing as there are no current ratings for the LD.

I tried to do things the "right" way and busted out my multi meter and tested the output voltage, which was just over 5V with no load which seemed right to me. Then I tried measuring the mA but had a hard time getting it where I wanted it, the adjustment didn't seem to go over 1mA, but I have never measured mA before and so I don't know that I was doing it right.

Output voltage with no load on a current regulated driver will be the maximum that the driver can supply. This is NOT the way to test a current regulated laser driver. You must use a test load. Testing without (the way you have) can result in the drivers output capacitor being charged to an excessive voltage, this means that when you hook your diode up to the driver that stored charge is dumped into the diode, killing it. Some drivers may just not like running without load at all.

That being said, I soldered the diode to it and with the potentiometer adjusted down, I could get the diode to glow just a little, but I couldn't get any major beam out of it. I tested the voltage again wondering if I had shorted something out, but still had the 5V I expected.

You need to measure current from the driver (this is why you need a test load, or a shunt on the driver), it's more important here than output voltage.

Should these 2 work together? According to my calculations I should be able to run it at 5V around 4mA, so I went back to look at the driver specs which listed 80mA as the low range, but that didn't seem right for the size, but it made me think maybe I had toasted the diode, so I tested it again on the battery with no driver and it worked great.

That driver requires a TTL signal to turn on, this signal is used to modulate the laser diode output. Did you hook the TTL+ pad up to a sufficient voltage source? Should these two work together? I don't know, there isn't enough information on that diode for me to give an answer there.

Any tips for a beginner?

Spend some time reading before you just jump in, it'll save you from costly mistakes.


See answers in red.

What voltage are you supplying the driver?

Where are you measuring the output voltage? How are you measuring it?

Do you have TTL+ on the driver hooked up properly? This is required for anything more than a few mA out of the driver.

Do you have a test load to set driver current properly with?

Do you know the current rating for your LD? Have a datasheet or anything?

I'm assuming you have the LD in a proper housing...

Got any pictures of your setup?
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Last edited by diachi; 04-05-2017 at 04:52 PM.
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Old 04-05-2017, 05:36 PM #3
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Default Re: Problems driving new diodes - low glow only

Thank you so much, your advice was spot on. I had failed to add power to the TTL+ not realizing that since I wasn't using TTL I would still need to do that. I got it working. I didn't get a spec sheet on that diode, so I didn't have any more info than you had.
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Old 04-05-2017, 05:44 PM #4
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Default Re: Problems driving new diodes - low glow only

Quote:
Originally Posted by ajhalls View Post
Thank you so much, your advice was spot on. I had failed to add power to the TTL+ not realizing that since I wasn't using TTL I would still need to do that. I got it working. I didn't get a spec sheet on that diode, so I didn't have any more info than you had.

Great! Yeah, figured it'd be the TTL+ pin. You can just connect it to the V+ input if you don't need modulation.

Hopefully the 80mA minimum from that driver isn't too extreme for that diode!
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520nm | Laserlands 520 | 5mW | For Review Awaiting arrival
532nm | Gearbest 303 Pointer | 50mW Metered
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Last edited by diachi; 04-05-2017 at 05:45 PM.
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Old 04-07-2017, 12:55 AM #5
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Default Re: Problems driving new diodes - low glow only

80 mA is way too much for that diode, expect about 1 mA per 1 mW for these diodes, plus a bit of threshold current (maybe 5 or 10 mA for something that small).

However, the driver is re-listed with a range of 20 to 500 mA in the description (title still says 80-500), so if you can actually adjust it down to 20 mA it could work out.

Otherwise just get a more powerful diode, the blu ray writer diodes are fairly cheap: Something from a PHR 803 sled will give you 100 mW or so of power and cost under $10. For a bit more you can get more powerful diodes quite easily.

Beware that this wavelength is not very visible but VERY dangerous to your eyes though!
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