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For a hobby project I recently bought a laser diode with the following specs:

Mitsubishi 645-655nm 350-500mw High-Power Red Laser Diode LPC-836

  • Power output: CW 380mW
  • Pulse Power: 570mW
  • Working Current: <340mA
  • Working Voltage: 2.2-3.0V
  • Sealed method: TO18 (5.6mm)

Naturally, the first thing I did when it arrived in the mail was to power it up using 3V DC. What I observed was a bright red light, but it was very spread out. Thus I have a few questions:

  1. Will the diode likely be destroyed with just DC current from two 1.5V batteries and no driver?

  2. Is the point of the driver to only provide a steady current? Could not a suitable resistor do the same trick?

  3. What is the point of the third pin on the laser diode?

  4. Is the light supposed to be spread out like that from a laser diode? I also bought a bag of cheapo 5mw laser diodes, that are mounted in a small brass housing and appear to have a simple driver attached. Would this housing be enough to focus the beam?

  5. Finally, in the case that I do need a driver to set this up correctly, would something like this do the trick?

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Will the diode likely be destroyed with just DC current from two 1,5V batteries and no driver?

Bare laser diodes are fairly sensitive to over-voltage and over-current conditons. They can also be quite sensitive to ESD.

Two series AA cells (for example) might have enough internal resistance to keep from burning out a laser like yours (fairly high power). Two D cells might not. YMMV.

Is the point of the driver to only provide a steady current? Could not a suitable resistor do the same trick?

A good driver will also ensure there's no current or voltage spikes on power up and shut-down, and protect against ESD.

What is the point of the third pin on the laser diode?

Many laser diodes are packaged together with a photodiode to monitor the light output (usually from the "back facet" of the laser). This allows hooking up the laser driver in a control loop to achieve constant power output, even if the laser temperature changes, for example.

Typically the 3rd pin is a connection to the photodiode. Usually the laser and photodiode share a common pin (either "common anode" or "common cathode") and the laser datasheet will tell you which way your device is wired.

Is the light supposed to be spread out like that from a laser diode? I also bought a bag of cheapo 5mw laser diodes, that are mounted in a small brass housing and appear to have a simple driver attached. Would this housing be enough to focus the beam?

Bare laser diodes tend to emit light in an cone of 30 degrees or more half angle. This angle can be very different measured "in-plane" and "perpendicular" to the top surface of the laser chip. Some laser diodes are packaged with lenses to collimate the beam so that it has less spread. The datasheet for your device will tell you the expected emission angle.

Finally, in the case that I do need a driver to set this up correctly, would something like this do the trick?

The driver you linked looks well matched in terms of current and voltage capability.

Whether it provides adequate ESD protection, soft-start, etc., is not clear from the E-Bay listing.

Final Note: 380 mW is more than enough laser power to cause permanent eye damage in case of an accident. Be sure you understand the risks and choose appropriate safety precautions before working with this device and work safely.

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  • \$\begingroup\$ Thanks for awesome comments. I'm well aware of the strength such a laser harbors. It appears buying an additional 3V laser pointer is far cheaper than buying housing, lens and a driver separately, so I'll probably buy something that looks suitable. I've marked your answer as accepted. \$\endgroup\$ – Pedery Oct 8 '13 at 18:17
  • \$\begingroup\$ For 3 pin laser diodes the 3rd pin is usually case connection. \$\endgroup\$ – ACD May 30 '17 at 17:31
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Mitsubishi LPC-836 has to have a current limiter to prevent it from burning out and limit its voltage as well. I attached my project below. This laser diode's third lead is a ground so there are two grounds as shown and can be combined. Its important to use heat conductive grease between the diode and its lens housing and to use a large heat sink on the LM317 regulator. Also this is very high power and will burn things so use eye protection against red laser light and us caution on with it is aimed at. Max burn range is about 3 feet. I had one burn out using a 4.1 ohm resistor but measurements were well below diode max limits so may be due to not using conductive grease on the first diode laser lighter

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