Inverting buck-boost converter

Thread Starter

anhnha

Joined Apr 19, 2012
881
This is an inverting buck-boost converter. As you can see in the picture, the output voltage is in the oppositive sign with the input.
Assuming that we want non-inverting output voltage, why shouldn't we just swap the output reference to get the positive?
I mean, for example, Vab = Va - Vb= -5V then Vba = Vb-Va= 5V. So why not choose Va as reference and have positive output voltage?

Buck-Boost Negative Output Voltage.PNG
 

AnalogKid

Joined Aug 1, 2013
8,537
Nothing on the schematic is marked Reference, Va, or Vb. Please try again.

And note that the input and output share a common Ground connection. For a non-isolated converter, "swapping the output reference", if I understand what you mean by that, can cause problems for circuits with other external connections.

ak
 

Thread Starter

anhnha

Joined Apr 19, 2012
881
Thank you. What will happen if the input and output don't share the common ground? Could you list some problems here?
 

AnalogKid

Joined Aug 1, 2013
8,537
For that condition you need a very different circuit, one with a fully isolated transformer. With almost any isolated topology, the output reference can be either output polarity.

ak
 
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