Galvanic Isolation for Safety: How Active Isolated Converters Can Remove the Transformer!

If you want to make your power converter safe, you need to add a transformer so that it has Galvanic Isolation... right? What is Galvanic isolation anyway and what does "Galvanic" mean?

Galvani become so famous, that his name actually began to mean "electric." "

Galvanic" refers to "Galvani" who made the discovery that led Volta to invent the battery. Obviously, once the battery was invented electrical research soared. So, Galvanic Isolation literally means "electric isolation." It does not mean magnetic or transformer isolation.

How can Galvanic Isolation Protect Me?

In the image at the top of the article, the transformer protects the human because the secondary side of the transformer can float to any common mode voltage and thus the common mode current, Icm_lk is zero- except any parasitic capacitance that might exist between primary side and secondary side.

Active Isolation: How Galvanic Isolation is Achieved

In a fully Active Isolated Buck-Boost converter, like the one shown below, Galvanic Isolation is achieved not by a transformer, but through precise control of the switches in a Buck-Boost topology with added switches on the lower return paths of the circuit.

The main challenge with this technology is not as commonly thought, "they are not really Galvanically Isolated", but instead the challenges are two-fold: 1) transformers are more reliable than transistors, and 2) Active Isolation generates internal common-mode currents that have to be compensated for or reduced to below allowable levels. GaN and SiC are the enabling technologies for these type of converters due to: higher voltage and power levels, and much lower Coss values. As wide bandgap device technology progresses, reliability, power levels, and Coss values will continue to improve, making transformerless isolation much more common.