# driving a 1000 mW laser diode

Started by February 7, 2018
```I want to power a laser diode (the kind used for engraving) in a
portable device for short periods with a 9V battery. The laser diode
comes in a tube with a focusing lens and trailing wires, and the spec
says 5V 1A.  This diagram seems to be the standard circuit for driving
these. The LM317 spec says Vout is 1.25V above Va and it needs 3V of

----------
+9V----o-----|  LM317 |---o-----o-----o-----o
|     ----------   |     |     |     |
|          |       >     |+    &mdash;     &mdash;
===         |     R1<    ===    ^     V D1
| C1       |       |     |C2   |D2   |
|          o-------o     |     |     |
|                  |     |     |     |
|                  >     |     |     |
|                R2<     |     |     |
|                  |     |     |     |
GND----o------------------o-----o-----o-----o

C1 = 0.1 uF
C2 = 1 uF
R2 = 3 * R1 (calculated to get 3.75V to Va and 5V to Vout)
D2 = 1N4148 or similar
D1 = laser diode

Would it also work with the simpler circuit using LM7805 regulator?
WouldI need the backwards signal diode at the end of this one too? The
LM7805 is supposed to put out up to 1A -- is it a problem that that
limit is right at the diode's current?

----------
+9V---o---| LM7805 |---o---- Vout = 5V (to laser diode)
|   ----------   |
===      |       === C2
| C1    |        |
|       |        |
GND---o-------o--------o----

C1 = 0.33 uF
C2 = 0.1 uF

thanks

```
```> I want to power a laser diode (the kind used for engraving) in a
> portable device for short periods with a 9V battery. The laser diode
> comes in a tube with a focusing lens and trailing wires, and the spec
> says 5V 1A.  This diagram seems to be the standard circuit for driving
> these. The LM317 spec says Vout is 1.25V above Va and it needs 3V of

I found another diode driverthat uses the LM317 for controlled output
current to a LED, but the example was for a much lower (not laser
diode) current:

---------
+9V-----| LM317 |----o
---------    |
|        >
|        < R
|        |
o--------o-----o-----o
|     |     |
|     |+    |
-    ===    V D1
D2 ^     |C1   -
|     |     |
GND------------------o-----o-----o

D1 = LED
D2 = 1N4001
C1 = 10 uF
R = combination of resistors and pot so
I = 1.25V/R

Would this work for a 5V 1A laser diode too?

```