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



Laser Pointer Store

The Tale of the Ghetto Driver

Toaster

New member
Joined
Aug 4, 2010
Messages
1,249
Likes
38
Points
0
So the volts aint doing the frying, its the amps huh... Ok So a 200ohm Will hold it out to work, Right?
 

MarioMaster

Well-known member
Joined
Jul 27, 2007
Messages
3,643
Likes
187
Points
63
well if the diode wants 2.15v at 30mA, then you are dropping 6.85v at 30mA.

6.85v / 0.03A = 228 ohm resistor value
 

Vaporizer

New member
Joined
Aug 6, 2010
Messages
382
Likes
25
Points
0
Well...volts frying? I can't say for sure. With LM317 drivers any "extra" volts is converted to heat. LD's I'm not that familiar with ..yet!

Now as far as the diode sheet specs.....it runs at 30ma, 2.15v. Lets give it 2.2v it's gonna need from the 9v battery and leaves 6.8v. (9v-2.2v).
Ok, plug 6.8v into the calculator and 0.030ma. You get 226ohms @ .204W.
So..a 220ohm resistor is pretty common and at 1/4W should work.

You can plug in diff values to simulate the voltage dropping and see what the current does. When it drops below the stated threshold current of 20ma, it should quit lasing.

Edit: I plugged it in and using the actual 2.15 as in Mario's example and a common 220ohm resistor you'll have 31ma.
 
Last edited:

Toaster

New member
Joined
Aug 4, 2010
Messages
1,249
Likes
38
Points
0
Thanks so much very helpful. In series they add dont they? So if i cant find a 2.2m I can get a 2m and 2 10's right? Thanks
 

Vaporizer

New member
Joined
Aug 6, 2010
Messages
382
Likes
25
Points
0
It's a very common resistor in most multi packs even from Rat Shack.
Red Red Brown. Tolerance band would be nice if gold, but you probably get silver.

I do remember reading abt battery voltage spiking killing diodes. You might want to put a capacitor (10-47uf) across the power leads too. Just remember to discharge it before connecting.
 
Last edited:

Toke

New member
Joined
Jul 25, 2010
Messages
1,111
Likes
55
Points
0
You made a good decision in getting some cheap diodes to practice on. :) And yes, resistors are added up when connected in series. The trick for connecting them in parallel is to invert the resistance to get conductivity, add that, and then re-invert the result back to resistance. A 4, 8, and 12 ohm resistor in parallel would be calculated such: 1/(1/4 + 1/8 + 1/12) = (1/0.458) = 2.18 Ohm
 

Toke

New member
Joined
Jul 25, 2010
Messages
1,111
Likes
55
Points
0
How would that be useful though, lol
Well, if you need a 3 Ohm resistor to set a LM317 to 400mA.
The 3 OHm's are not easy to find, but 6,1 Ohm's are, and two of them in parallel is close enough to 3 Ohm.
 

Vaporizer

New member
Joined
Aug 6, 2010
Messages
382
Likes
25
Points
0
Here is an easy online parallel resistor calculator.
PARALLEL RESISTOR CALCULATOR

The internet introduces an international community. English isn't everyones 1st language.
Many things on forums can be seen as "not how we do/say it", but the intent/content is normally easily understood. When I post anything that has measurements, I always include the mm equivalent as a courtesy. 99% of the world uses the metric system, we normally don't.
 

Toaster

New member
Joined
Aug 4, 2010
Messages
1,249
Likes
38
Points
0
Sorry I didn't know ,s were standard :) I lave in US but I still think Metric makes more sense
 

Vaporizer

New member
Joined
Aug 6, 2010
Messages
382
Likes
25
Points
0
Toaster, have you measured the output of the driver where it connects to the dummy load? Just to see if the voltage is making it that far? From there you should be able to measure just after each diode and see a .7v drop. That would prove the driver is outputting and confirm each diode is working and installed correctly.
No output at the driver would mean its bad, or the connections are wrong someplace.
 




Top