SW-LD73 Laser driver modification.

This laser driver board seems to be common for many <20W LED lasers used for cutting/engraving.

Whenever powered on, it defaults to full power due to a rather strong internal pull-up.

Most CNC machines have a laser TTL PWM output that goes into high-impedance mode on boot. In that case, any connection to, or reboot of the microcontroller will make the laser output full power for about 2 seconds while the user may not be prepared for that.

D3, in the red ring, provides power for the pullup.


The solution is to remove D3, which provides power to the pull-up, then the laser will not be “default on” anymore.