What are the usage of isolated AC-DC converters and non-isolated AC-DC converters respectively?

Considering AC-DC converters, insulation is necessary to protect human bodies from electric shock. To use isolated AC-DC converters, since the GND of a noise sensitive circuit can be separated from the other circuits' GND, the noise immunity can be secured.  Isolated AC-DC converters are realized with using transformers.

Isolated AC-DC converters are used to secure the safety of secondary output short or for countermeasure against the electromagnetic noise. Further, in wide input voltage range, power convert efficiency is good.

On the other hand, non-isolated AC-DC converters can be designed in small size compared with isolated AC-DC converters. If the circuit is in an insulated housing, electric insulation is not necessary, so non-isolated AC-DC converters can be used. The typical application is LED lighting.

AC-DC converters of Ricoh, R1700 series are non-isolated PFC ICs.

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