Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Another diode goes to the graveyard

the lm317 is not used how it normaly would be its setup in current regulation mode, it will set the current to the desired amount.

...lazer.. ;D ;D ;D
 





The current into the LM317 is always higher than the output, by the amount of power it's dissipating in heat.  The larger the difference in input vs. output voltage, the more current will be dissipated - that's why mine's on a large heatsink.

Anyway, now that you mention it, I didn't see any condensation on the outside, so I guess there wouldn't have been any in/near the LD.

I guess it was the spikes from hooking up power with the current up that close to the max.  Makes me want to look into a soft-start mode.  Maybe feed the input power through a resistor into a big capacitor.
But next time I'll probably keep it down to 500mA.

Oh well - it was cool while it lasted (no pun intended).
 
Zarniwoop said:
The current into the LM317 is always higher than the output, by the amount of power it's dissipating in heat.
Click to expand...

Are you 100% sure? As I recall the current was the same...the voltage is being dissipated as heat. I will need to double check it.
 
Zarniwoop said:
The current into the LM317 is always higher than the output, by the amount of power it's dissipating in heat.  The larger the difference in input vs. output voltage, the more current will be dissipated - that's why mine's on a large heatsink.
Click to expand...

Sorry, I beg to differ...  If you're using the LM317 as a series current regulator, the current in should be the same as the current out.  There's only one path for the electrons to flow in a series circuit... thus the current is the same everywhere in the circuit.  Any power (heat) to be dissipated by the regulator is a function of the current multiplied by the voltage drop across the regulator.  The voltage drop across the regulator will change as the input voltage increases but the current will remain constant.
 
Hmm...I guess I stand corrected here. I'll have to go measure it.
Now I'm wondering how I could be measuring 750mA in, but 550-600mVacross a 1 Ohm resistor in series with the diode.
 
Zarniwoop said:
Hmm...I guess I stand corrected here. I'll have to go measure it.
Now I'm wondering how I could be measuring 750mA in, but 550-600mVacross a 1 Ohm resistor in series with the diode.
Click to expand...

Could it possibly be the resistor does not have a high enough wattage rating? Just curious what is the wattage rating of your resistor and the tolerance? Mine have a 5% tolerance but they all measure 1 ohm.
 
Okay - The discrepancy I was seeing must be a combination of the inaccuracy of my old bench supply's current meter (most likely), and possibly an extra 5% from the resistor I'm using for current measurement.

Thanks - I'll know better next time.
 
I find it fun to send a huge 6 inch static spark through them. ;D

Broken diodes of course.
 
Should be okay - it's a 1 Watt, 5%. Didn't have a local source for 1%.
OTOH...
This particular circuit is still on a proto-board using maybe #24 wire (if I remember my wire gagues - it's that multi-colored copper phone wire). Maybe I was trying to push too much current through all that.
Next run I'll move it off the proto and built it properly.
 
You must log in or register to reply here.


Back
Top