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I came across this design which generates +1.5V and 1.5V from https://simple-circuit.com/arduino-ac-current-measurement-current-transformer/) enter image description here

My question is: with the same DC/DC isolated transformer, wouldn't it be possible to generate -1.5v with a second positive LDO LT1761 circuit by connecting its output to GND making its "gnd" a -1.5V?

Something like this ugly drawing:

enter image description here

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Yes it would be possible. And usually positive regulators are cheaper and more available than negative ones, so they would be preferred (all other things being equal).

Take care to account for what happens if one of the rails pulls the other past ground due to loading (or during transient conditions). A couple of Schottky diodes (one across each output to ground) will eliminate most of the concerns.

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  • \$\begingroup\$ Thanks. I don't get what you mean by "one rail pulls the other past ground". If there's a transcient, on a single rail, its voltage will be offsetted and what? Is it for components that uses both rails? like AO that will output wrong values? \$\endgroup\$
    – Julien
    Sep 13, 2022 at 7:12
  • \$\begingroup\$ @Julien Imagine loads between rails. Transient conditions- consider start-up where the +5 appears before the -5 (as it will in this case) so the regulator for the negative rail has to start with initial supply voltage < 0V before it goes positive. It may not like that. \$\endgroup\$ Sep 13, 2022 at 7:23

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