These diodes are not like normal Light Emitting diodes (LEDS), these diodes can use all the available power if not controlled. So it need to be attached to a current controlled DC source.
The Laser Diode(LD) module contains an Photo diode inbuilt, which monitors the output light intensity and used as a feedback for the control circuits. The terminals from laser diode are
- Laser Diode Cathode (LDA)
- Photo diode Anode (PDA)
- COMMON Positive
This is a simple description of cheapKeyChain Lasers that are sold for 5 bucks or so.The laser diode head has three pins labeled: LDC (Laser Diode Cathode), PDA (Photo Diode Anode) and COM+ (common Positive Terminal).Inside the laser diode head we find the laser diode itself and a photodiode, used to regulate the laser diode current with an external feedback loop.
A Schematic from MAXIM