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 headroom.
----------
+9V----o-----| LM317 |---o-----o-----o-----o | ---------- | | | | | | > |+ ? ? === | R1< === ^ V D1 | C1 | | |C2 |D2 | | o-------o | | | | | | | | | > | | | | R2< | | | | | | | | GND----o------------------o-----o-----o-----oC1 = 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