I've carefully read Wikipedia article and can't get one important thing - is there galvanic separation in such supply?

The diagram in that article goes like this:

SMPS block diagram

What I see here is that the transformer is only on one path and there's the "output->chopper controller" path that bypasses the transformer. Usually the transformer is the unit that performs galvanic separation.

Does this mean a switched-mode power supply doesn't feature galvanic separation between the input and the output? Is it possible for unlimited current to flow through the power supply?


2 Answers 2


Not all SMPSs provide galvanic separation. DC/DC converters transforming between two low voltages in a circuit often don't. The block diagram, however, shows a mains connected SMPS, and most of those do have galvanic separation.

The feedback often goes via an opto-coupler, which indeed is missing in the article's block diagram. The signal is PWM, so a normal (digital output) opto-coupler can be used.

  • 2
    \$\begingroup\$ Does this imply there's galvanic separation thanks to the opto-coupler? \$\endgroup\$
    – sharptooth
    Commented Jun 6, 2011 at 14:43
  • 4
    \$\begingroup\$ @Sharptooth - Yes. In the forward path it's the transformer, in the feedback it's the opto-coupler (between the chopper controller and the inverter chopper). \$\endgroup\$
    – stevenvh
    Commented Jun 6, 2011 at 14:52
  • 1
    \$\begingroup\$ Schematic showing opto-isolation block diagram showing isolation in feedback \$\endgroup\$
    – endolith
    Commented Jun 7, 2011 at 18:47

It depends on the supply. The ones used for laptops and mobile phone chargers have an isolated output which is achieved with a transformer. The high frequency used means that it can be very small.


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