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| Laser driver |
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| Raj:
I wanted to drive a numb08 laser diode. I'm thinking of using lm338 to build a supply that'll limit voltage to 4.5v max, and 2.77 A current. I'll use multiple Tvs diode and Zena diode, right next to laser diode for protection. I want to ask, is it good enough? Do I need to change anything? |
| Zero999:
A laser diode only needs the current to be limited. The forward voltage will sort itself out. Only one LM338 is required to regulate the current. The supply voltage is 5V and the LM338 needs 3.75V across it ore more to regulate the current to the desired level. The laser diode could drop as much as 4.8V, so you need an 8.55V supply, in order for it to work. The overvoltage protection diodes will not do anything and aren't needed. A simple series resistor would stand more of a chance of working, than the complex circuit you've posted. |
| danadak:
If you decide to modulate diode the regulator transient response may be of concern. Regards, Dana. |
| janoc:
--- Quote from: Hero999 on November 08, 2017, 12:06:27 pm ---A laser diode only needs the current to be limited. The forward voltage will sort itself out. Only one LM338 is required to regulate the current. The supply voltage is 5V and the LM338 needs 3.75V across it ore more to regulate the current to the desired level. The laser diode could drop as much as 4.8V, so you need an 8.55V supply, in order for it to work. The overvoltage protection diodes will not do anything and aren't needed. A simple series resistor would stand more of a chance of working, than the complex circuit you've posted. --- End quote --- Eeeep! Do not drive a laser diode with a simple resistor! That will work for a short term test but it is a very poor solution. It is the best way how to turn your laser diode into a crappy LED - exceeding the diode current or optical output power even for a very short time (e.g. because of temperature fluctuation) will kill the optical surfaces and it won't lase anymore - and a simple resistor or a constant current driver has no way to prevent this. These are bare laser diodes, you will absolutely need a driver with an optic feedback to limit the output power because that changes both with temperature and with the diodes aging. Moreover, that NUBM08 is a pretty beefy 38W bank, LM338 will be very going very hot if you try to use it as a constant current driver. Furthermore, you will likely need one for each of the diodes (NUBM08 is a bank of 8 lasers), if you put the diodes in series you will need a fairly high voltage supply. Have a look here to see how to correctly (and safely) drive semiconductor lasers: http://www.repairfaq.org/sam/laserdps.htm#dpstoc |
| Raj:
--- Quote from: janoc on November 08, 2017, 03:12:39 pm --- Moreover, that NUBM08 is a pretty beefy 38W bank, LM338 will be very going very hot if you try to use it as a constant current driver. Furthermore, you will likely need one for each of the diodes (NUBM08 is a bank of 8 lasers), if you put the diodes in series you will need a fairly high voltage supply. http://www.repairfaq.org/sam/laserdps.htm#dpstoc --- End quote --- nice point but, I have a single diode. Lol |
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