I saw a post some time ago where the person made a power supply which has what he called floating outputs.
What are the floating outputs of a power supply and why would you need floating outputs?
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3 Answers
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It simply means that the output side of the power supply is completely isolated from the input side, not even sharing a ground connection. This allows the power supply to be used to insert a voltage into a circuit without reference to any other power supplies already in the circuit. For example, you might use a floating 12 V power supply to drive the gate of a high-side N-channel MOSFET in a high-voltage switching regulator.1 More commonly, this allows the power supply to be used with either the negative terminal grounded or the positive terminal grounded.
1 For this kind of application, you also need to know the "isolation voltage rating" of the floating power supply — i.e., how much voltage can it withstand between its input side and output side — and be careful not to exceed it.
answered Oct 31, 2023 at 12:29
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It could be a power supply where both parts of the output - the "hot" side and the "return", are not referenced to anything, such as an external ground.
Many lab/bench supplies are built with this feature.
This allows the user to reference (ground) the supply outputs as best fits his/her application. It also allows the user to better control current flow, particularly return currents.
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If you've ever work on a product for the military or a satellite, you're probably familiar with a standard, boiler plate requirement that the input to and outputs from a power supply be isolated by at least 1 Mohm. Sometimes, because of output to input feedback for the control loop, this requirement is not practical to meet without increases in complexity and cost, and so deviations are granted to reduce the amount of isolation required. But that doesn't reduce the need to isolate inputs from outputs.
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4\$\begingroup\$ This also allows you to series connect 2 such supplies to get 2 rails, possibly grounding the centre tap, possibly not. And the rails don't have to be symmetric. I did a lot of work optically characterising GaN HEMTs, and they need a negative gate bias to turn off. Floating bench supplies make that trivial. \$\endgroup\$– Chris HCommented Oct 31, 2023 at 15:03
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Floating power supplies have advantages in many applications. For example in sensor applications that are very sensitive to noise or net-induced power spikes.
You can always filter, but you can significantly lower noise by having a insulated PSU. You may, however, run into other disadvantages by not having common ground in your system.
Here is an interesting article on the topic: Comparing Voltage: When to Ground a Floating Power Supply
