Ground offset for PSU and Fan?
Hey guys,
I have an i3 mk3s that I'm creating a conversion kit for doing CNC laser cutting with a 3.5w diode laser.
My plan was to use a buck converter to drop the 24v PSU output down to 12v to drive the laser, and to use the print fan's signal for PWM control (similar to what this guy did).
What I've found though is that the GND signal from the PSU has about a 5v offset from the GND signal for the print fan, so when I hook up my circuit the fan is on 100%. This means that the laser is also on 100%, and I can't use gcode to control the duty cycle.
I have no idea why the Einsy board would be designed this way. I could use an external 12v source and call it done, but I kind of want to figure out a way for the laser mod to be self contained. Does anyone have any ideas?
My circuit diagram is attached.
Best Answer by Dreide:
Note that the PWM control of the fan switches GND, not +5V. See Einsy schematics.
RE: Ground offset for PSU and Fan?
Note that the PWM control of the fan switches GND, not +5V. See Einsy schematics.
RE: Ground offset for PSU and Fan?
Yep. It's like this...
RE: Ground offset for PSU and Fan?
Ah I didn't think they would be low-side switching. Thanks for the schematics guys, I was having trouble finding them yesterday.
RE: Ground offset for PSU and Fan?
Hi @garagetimewithdavid,
I know this past is quite old but i struggle with the same problem. When connecting the output of my step-down to both fan and laser as in this image from the instructables post my laser is "always on"
Did you solve this and is, can you explain how?