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

  1. Laser Diode Cathode (LDA)
  2. Photo diode Anode (PDA)
  3. 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






Hello, I am Asim admin of this blog. An expert in Scientific Instrumentation (Analytical Instrumentation). My works are always associated with both Physics and electronics. Currently working on ARM based embedded systems for Optical(UV and Visible) and electrochemical spectroscopy (EIS). My M.Tech. Thesis was related to all these things. I had worked for a 8 bit microcontroller based standalone EIS (electrical impedance spectroscopy) device. I have Masters in Instrumentation engineering from NIT Kurukshetra,Haryana and Masters in Electronics Science from Sambalpur University, Odisha (Formerly Orissa/Utkal) Am also work for PHP MySQL AJAX based CMS design. i love blogging and coding(am not an expert).

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