"Borrow" GND for a 12v linear regulator?



  • The Duet Wifi uses a common ground plane for all voltages, correct?

    Reason for asking is that I am converting my machine to 24V, but want to keep my 12V fans.

    I figured i would use a LM2940CT-12 LDO given a nice small form factor and low power requirement of the fans.

    My plan is to take the V_IN from the V Fan Jumper Select to power the LDO and drop the output back into V_FAN. But about GND, would it be safe/advisable to use GND from 5V EXT or an endstop, or the expansion connector?

    Yes, I could of course also just use the main power input and use that. It just seems more un-clean 🙂

    On a less serious suggestion, i suppose i COULD use the +5V in the V_FAN as GND as the voltage differential would be more then sufficient still. But.... I won't 🙂



  • All but the thermistors use a common ground yes, they have an extra fuse to ground to protect the processor.

    I removed both jumpers from int_5v_enable and v_fan selector and and took ground and v_in* from those pins, supplying the output back to v_fan. (as well as shorting int_5v_enable and ground to maintain the function of the jumper i removed there). I simply took a one of those stackable headers from an D1 mini kit as it provided long leads to bend and solder in place where they needed to go.

    *)i say v_in, but its fused from F2.

    2eeeb8fb-b48c-4d82-87fe-3b734547dfe4-image.png



  • @bearer said in "Borrow" GND for a 12v linear regulator?:

    All but the thermistors use a common ground yes, they have an extra fuse to ground to protect the processor.

    I removed both jumpers from int_5v_enable and v_fan selector and and took ground and v_in* from those pins, supplying the output back to v_fan. (as well as shorting int_5v_enable and ground to maintain the function of the jumper i removed there). I simply took a one of those stackable headers from an D1 mini kit as it provided long leads to bend and solder in place where they needed to go.

    *)i say v_in, but its fused from F2.

    Ok.. that's a clever little design indeed. My hat is off to you. 🙂



  • The dc/dc converter is a jelly bean part off the great candy mountain in the far east; caveat emptor, not all are rated for 24V, few 26.5 which I needed so it let the smoke out ... clever on paper, thats my motto 😉



  • My system is 24v based, and so to get 12v for a duet board\case fan, I just used one of the "Always On" fan outputs, and fed it into a a standard 7812 regulator with a couple of suppressor caps on the input\output of the chip.

    Under RRF2, I was just driving the fan in parallel with the hot end fan, so that it would come on when the hot end reached 45 degrees, but since going to RRF3, the fan would produce an annoying 'whistle', frequency of which would depend on the settings. But since the mod, peace & quiet returns....


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