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I'm building a dual-rail power supply and need to drop about 5-10 V from the rectification output. It's for powering an amp so I need low noise and about 2A therefore I opted for linear regulators. Most schematics online use a positive and negative regulator for each rail, but I was wondering if my circuit below would work using the same regulator, one on the positive rail and one on ground.

Simulating it shows the correct output voltages, but what are the drawbacks to this design vs using a negative voltage regulator for the negative rail? Does it have power or stability issues/ there must be a reason designs keep using negative regulators.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ As already said, stick with positive and negative linear regulators. A positive linear regulator can only source current - they don't have push/pull outputs, its not like an op-amp. Similarly, a negative linear regulator can only draw current. Take a look at the internal schematic of a 7805 for example. \$\endgroup\$
    – TonyM
    Jan 25 '18 at 14:17
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Simulating it shows the correct output voltages, but what are the drawbacks to this design

No it won't work very well. Reason: the load could be asymmetrical and try and lift the mid-rail point towards V+. This is highly likely in an audio amp.

The way the lower regulator is configured means that it cannot prevent this from happening because no matter what it does, its pass-transistor cannot act like a shunt voltage regulator to pull mid-rail back to the mid-point.

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    \$\begingroup\$ +1 Yup.. this only works if the negative side ALWAYS uses more current than the top side. \$\endgroup\$
    – Trevor_G
    Jan 25 '18 at 14:03

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