Laser Diode Use Problem

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Joey713
 
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Joined: Thu Nov 22, 2018 5:37 am

Laser Diode Use Problem

Post by Joey713 »

Hi, all
I have a circuit where the base transistor (PN2222a) leg is plugged into the pin 9 of the Arduino. When I power everything up and send the signal from the Arduino to the transistor base leg, the laser diode doesn’t light up, but my design strictly follows Complete Tech Guide to Laser Diodes(source as reference: https://www.BANNED.net/electron/the- ... iodes.html). In addition, the Arduino is powered through a cable that is plugged into the computer and I am using a LED rocker switch if that helps.

Is there anyone has ideas? Thank you in advance.
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adafruit_support_mike
 
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Re: Laser Diode Use Problem

Post by adafruit_support_mike »

That circuit won’t work. The capacitor has no way to discharge.

You’ll get a short burst of current as the capacitor charges to 9V minus the laser diode’s voltage, then nothing else can happen.

You’ll get better results with a circuit like this:
laser-diode-driver.jpg
laser-diode-driver.jpg (34.77 KiB) Viewed 91 times
The two diodes at the lower left are a simple voltage source. The voltage across the upper one will be about the same as the voltage between the transistor’s base and emitter. That forces the voltage across the 10 Ohm resistor to be about the same as the voltage across the lower diode.. somewhere around 0.6V.

It takes 60mA of current to produce 0.6V across a 10 Ohm resistor, and the transistor will make that happen.

The current to the 10 Ohm resistor has to pass through the laser diode, so the circuit drives the laser with constant current.

You can change the current by changing the value of the resistor.

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