Laser Line

Started 7th October 2020

There is a common type of laser, that goes by something like "12mm Red Laser Head Diode Tube 650nm 5mW Dot or Cross Line Module" on ebay. They come in versions that display a line, a cross or a dot. Interestingly they contain laser diodes with a built in photo-diode and electronics which use the photo-diode to control the power output. The model number is SYD1230.

The first set of photos show a version which uses an integrated circuit for power regulation. Click to view full size.

Laser line, David PillingLaser line, David PillingLaser line, David PillingLaser line, David Pilling

The second set of photos shows a version using discrete components.

Laser line, David PillingLaser line, David PillingLaser line, David PillingADL-65055TL laser-diode, David Pilling

Removing the lens, different lenses and the laser diode.

Laser line, David PillingLaser line, David PillingLaser line, David Pilling

Searching for clues on the discrete driver, there are:

KEYCHAIN LASER DRIVER CIRCUIT by Le Magicien
Sam's Laser FAQ, Toshiba Laser Diode Power Supply (TO-LD1)

The typical three pin semiconductor laser package consists of a laser-diode and photo-diode with a common connection which goes to the positive supply voltage. The two separate connections are the laser cathode and photo-diode anode.

Laser diode connections, extract from ADL-65055TL datasheet

In normal operation the laser-diode is forward biased and the photo-diode is reverse biased (pin 2 is positive relative to pins 1 and 3), as the light output increases the current flowing through the photo-diode increases.

In general for a discrete driver there would be a transistor driving the laser, and another transistor connected between the driver base and the photo-diode in such a way that more photo-diode current reduces the driver base current and hence the current in the laser-diode.

The actual schematic is shown below (click to expand):
Laser line schematic, David Pilling

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Page last modified on October 18, 2020, at 01:07 AM
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