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FrozenGate by Avery

Driving laser diodes in parallel?

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LikeitBright

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Just curious, has any one driven several (2 or more) laser diodes in parallel using just the one driver? Any problems or issues that cropped up? Perhap the current limiting wouldn't work so well here and a separate driver is needed for each LD?
 





LikeitBright said:
Just curious, has any one driven several (2 or more) laser diodes in parallel using just the one driver?  Any problems or issues that cropped up? Perhap the current limiting wouldn't work so well here and a separate driver is needed for each LD?
Click to expand...

In parallel, the voltage output of the driver would be the same, but the current would be split between the diodes. It would be ideally split equally with similar diodes, but depends on the apparent resistance of each. So, if you wanted to drive two diodes at 300mA, your driver would have to put out 600mA.

You could also do them in series, but the output voltage will be doubled, while the output current will be the same through both, or equivalent to the output current of the driver.

I personally haven't tried, so I don't know if there are any problems with doing this, as I'm just going on theory. But, if you want to be the guinea pig, go for it ;D
 
I think it's a bad idea. The current will choose the path with the least resistance and the diodes aren't completely identical. Some might work at 3.0V or 2.8V or 3.1V etc. So if you conect two (or more) diodes in parallel, so will the one with the lowest voltage get most of the current. For example: one will only get 200mA and the other will get 400mA (600mA total). The diode with the highest current will soon die, and when it does will the other diode get 600 mA and die in an instant.

That's why parallel is bad and series is good because the current is the same anywhere in the circuit. Or use two drivers.
 
Yes, I agree on the theory - its the practical downside that may come back to bite me I'm thinking of ;)

My main concern is the unequal current issue which is why series is starting to sound better at this point. Then again, a micro-drive for each module will cost $70 total so thats not too bad.
 
FireMyLaser said:
I think it's a bad idea. The current will choose the path with the least resistance and the diodes aren't completely identical. Some might work at 3.0V or 2.8V or 3.1V etc. So if you conect two (or more) diodes in parallel, so will the one with the lowest voltage get most of the current. For example: one will only get 200mA and the other will get 400mA (600mA total). The diode with the highest current will soon die, and when it does will the other diode get 600 mA and die in an instant.

That's why parallel is bad and series is good because the current is the same anywhere in the circuit. Or use two drivers.
Click to expand...


Agreed.



If they were two equal diodes i'd try it, but not with different diodes that need different currents.
 
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