Hi, sorry for my noob question

[GatoX]

Hi everyone. I'm thinking in make a tiny red laser from a 10440 flashlight host, LPC-826 diode and linear driver, but I'm thinking that the voltage may fall short. Anyone knows the voltage drop of a LM317? I have a few and I'm considering use how driver :thanks:

 

[marcuspeh]

It is around 3v

 

[GatoX]

If I power the lm317 with 3.7V I will get only 0.7v??

 

[marcuspeh]

Around there. To power red, you will need around 5.5v

 

[GatoX]

thanks for the info, I will use a host of two batteries

 

[Deleted member 49011]

If you run the LM317 in constant current you have the drop of the current set resistor at 1.25 Volts plus the 2-3V drop over the regulator plus the laser diodes voltage drop .

 

[Evans]

It may above 3v ,
you can upload this picture to google and it will return you the similar product and then you can click for more info.

 

[Benm]

There are low drop out regulators that work similarly to the LM317, but you will still lose the 1.25 volts across the sense resistor regardless. You will end up needing 2 batteries in series with this approach.

Running a linear driver to power a red off a single cell is quite a challenge. It can be done, but probably not reliably with commonly available components. You'd either need to work with a low-vgs-on mosfet or a dedicated chip like the amc 3175. The latter has a fixed current of 350 mA or so, which might be a bit much for something small.