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Can the TL783 be used to regulate negative voltage by connecting the output to my system ground and using the regulator ground as my negative voltage source? I couldn't find anything in the datasheet pertaining to negative regulation except something like this:

The device works to keep the voltage at the OUT pin 1.25 V higher than the voltage at the ADJ pin. Therefore, a resistor divider can be used to set the output voltage.

This would lead me to believe it should work as I described, but I'd like to verify with someone who knows more than me about this.

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  • \$\begingroup\$ this could work, but it's easy to mess up, specially if your circuit also needs positive supplies. If you post a schematic and details about the loads we can give a better answer \$\endgroup\$ – FrancoVS Oct 31 '17 at 17:40
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Assuming you want the ground of the load to be the same net as the ground of your input power source, it won't work. In your proposed circuit the regulator can only dump more or less current from a positive supply into the ground net. It doesn't have any way to control the current drawn from the load's negative terminal.

What you want is a negative linear regulator. LM7905 is a low-cost one for -5 V. LM337 is a low-cost adjustable output one.

You will also need an input power supply more negative than the voltage you want to apply to your load.

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  • \$\begingroup\$ But since it's negative voltage, wouldn't there be no current drawn from the negative terminal, only sunk into it? \$\endgroup\$ – Billy Kalfus Oct 31 '17 at 17:50
  • \$\begingroup\$ Drawn out of the load's negative terminal. Sunk into the supply's terminal. \$\endgroup\$ – The Photon Oct 31 '17 at 17:59
  • \$\begingroup\$ Possibly not true - this sort of scheme can work if you have two separate (unregulated) power supplies and treat them as a series connection of power supplies. The middle node is then ground. Granted it's probably easier and cheaper to pick up a 790x and design it properly... \$\endgroup\$ – awjlogan Oct 31 '17 at 18:04
  • \$\begingroup\$ @awjlogan, edited. \$\endgroup\$ – The Photon Oct 31 '17 at 18:13
  • \$\begingroup\$ I can find an input supply more negative than what I need for output. The problem is I need to regulate about -100V down to about -60V (at very low current), way out of spec for the 7905 \$\endgroup\$ – Billy Kalfus Oct 31 '17 at 18:22

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