Electronic – How is galvanic isolation established in an SMPS

isolationswitch-mode-power-supply

I can understand how an isolation transformer can establish isolation but since SOME SMPS supplies don't have transformers and they have rectifiers instead I wonder how the AC and DC ends are isolated.

Edit: Here is an SMPS with no galvanic isolation.

Here is the datasheet which says there is no galvanic isolation.

How is that possible?

I'm asking because people here all agreed SMPS has small transformers which isolates the input and output power.

Best Answer

Sure they have transformers: -

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The transformer looks different to a regular AC type but it's still the largest single component on the PCB but a whole lot smaller than it would be for 50/60 Hz operation. The transformer is the big yellow taped thing in front of the heat sink at the back/left.

SMPSs also use opto-isolators for feeding back a measure of the output voltage so that it can be regulated. This is another significant isolation feature thus, output and input remain galvanically isolated to several kV and are therefore "safe".

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