Laser diode power questions

[Scott Johnson]

I'm playing around with a 30mw laser diode. It says that it's 5v input. I'd like to eventually power this with batteries. However, with my desktop AC power supply I have it set to 4.5v DC for testing and it seems that it works ok. It may be a little dimmer than I'd have hoped though.

So two questions
1) If I run 3 x 1.5 v DC (3 AA batteries) straight to the diode, do I have to worry about burning out the diode
2) If I wanted to run 4 x 1.5 v DC (4 AA batteries) is it as simple as adding in a resistor to bring the power from 6v to 5v? If so, how do I calculate the resistor?

Thanks!

 

[kellys_eye]

Have you looked at the manufacturers data sheet for the device? What is the actual device number?

 

[Scott Johnson]

Unfortunately, no. I don't know what the device number is... It came from China and it didn't come with spec sheets.

 

[davenn]

Unfortunately, no. I don't know what the device number is... It came from China and it didn't come with spec sheets.

does it already come with a driver circuit ?
if not you will need to get/build one and without spec's that's going top be really difficult ....
you cannot just put voltage from a battery/other PSU straight across the diode, you will damage/destroy it

 

[Scott Johnson]

Its a self-contained unit... I don't think it's just a diode? This is similar to what I have: https://www.ebay.com/itm/Focusable-...397352?hash=item1ed6f4f7e8:g:dXUAAOSwJtdaTDye

 

[kellys_eye]

Without knowing what they are actually using as a current controlling device it isn't reliable to operate it at anything other than the voltage specified. If they genuinely mean '5V' then it's likely that it's just a series resistor to limit the current - pretty crappy as far as laser diodes are concerned. A decent driver would be constant current and have a wide(ish) voltage range.

Stick to 5V (or as close to it as you can) - a 4.5V battery will be ok, use a 6V battery by fitting a series diode (to drop 0.6V) or a low drop-out regulator for higher voltages.

 

[Bluejets]

You could add a little dc dc converter to the 6v supply( or whatever battery you have in the required range) . They cost about $1.00 off Ebay.
Just need to adjust to the required 5v output.

Edit: Note these are a step-down unit. There are others that go up or down.

https://www.ebay.com.au/itm/Mini-DC...046604?hash=item53fdd7894c:g:T5EAAOSwe09Z-o7p

 

[Externet]

The one on the Ebay link is a module containing a laser diode and driver circuitry. It regulates the laser current for variations in supply voltage. How big can the variations be is in the always absent chinese data sheets, but perhaps can be found for similar modules/schematics.

 

[davenn]

Its a self-contained unit... I don't think it's just a diode? This is similar to what I have: https://www.ebay.com/itm/Focusable-...397352?hash=item1ed6f4f7e8:g:dXUAAOSwJtdaTDye

The one on the Ebay link is a module containing a laser diode and driver circuitry.

as long as it is the SAME as the one in the link .... SIMILAR mite be a dangerous assumption

indeed it does say driver


Dave

 

[Scott Johnson]

Without knowing what they are actually using as a current controlling device it isn't reliable to operate it at anything other than the voltage specified. If they genuinely mean '5V' then it's likely that it's just a series resistor to limit the current - pretty crappy as far as laser diodes are concerned. A decent driver would be constant current and have a wide(ish) voltage range.

Stick to 5V (or as close to it as you can) - a 4.5V battery will be ok, use a 6V battery by fitting a series diode (to drop 0.6V) or a low drop-out regulator for higher voltages.

So it will be a diode to drop the voltage down .5 volts and not a resistor?

 

[Externet]

If the laser pointer was meant to be used only with a fixed voltage as "5V", a resistor would suffice and the chinese would not spend half a penny extra in its manufacture implementing circuitry. But the driver circuit implies the constant current is produced from the components, so it should accept varied voltages as in aging batteries. How varied is the question, as there is a few style boards used in pointers/modules and perhaps someone else can find their schematics to learn variables, or reverse engineer :
----> https://duckduckgo.com/?q=laser+pointer+driver+board&t=canonical&ia=images&iax=images
The constant current setting potentiometers are another section of the driver circuitry, not necessarily telling the input V range.

To my suspicion, these cheap pointers should be capable of handling 12V input, their internal regulator will take care of that.
If smoke escapes, they are available at the 99 cent store.