Those who have worked with high-voltage equipment before can readily appreciate the benefits of electrical isolation.

When two devices or circuits are in communication, DC currents and AC signals typically flow freely.

In low-voltage systems, this is a safe way for two parts of the system to work.

However, when high voltage enters into one or more parts of the system, freely-flowing DC current and some AC signals can cause errors, physical damage, and/or create hazardous conditions of operation [Tex20a].

A solution to this problem is galvanic isolation:

Alternative definitions:

• IEC’s definition is high-level: “Arrangement within equipment that permits the transfer of signals or power between two circuits without any direct electrical connection between the two.”
• IEEE’s definition [IEE14, p. 2] takes effort to interpret: “A method of electrical isolation where neither the signal nor the common of the output of the isolator is dc-coupled to the signal or common of the input of the isolator, except for low-level leakage associated with nonideal components.”

Galvanic isolation can help 1️⃣ protect human operators from electrical shocks, 2️⃣ prevent ground loops, and 3️⃣ improve noise immunity (and thus maintain signal integrity); see Fig. 1.

In Fig. 1,

• A ground loop is a potentially detrimental loop formed when two or more points in an electrical system that are nominally at ground potential are connected by a conducting path such that not all points are at the same ground potential [IEE19, p. 91].

• For improving noise immunity, an isolator with high common-mode transient immunity (CMTI) is necessary.

  CMTI is the maximum tolerable rate of rise or fall of the common-mode voltage applied between two isolated circuits [ZB18].

Isolator devices are available in three primary technologies as shown in Fig. 2: 1️⃣ optical, 2️⃣ inductive, and 3️⃣ capacitive.

Each technology uses a different insulator material with different dielectric strengths.

• Dielectric strength is a measurement used to describe the maximum applied electric field, in volts per meter, that a material can withstand without undergoing electrical breakdown and becoming electrically conductive [Tex20a].

Here is how the technologies compare [Sch17, Tex20a]:

Power converters are typically isolated using use either transformer or coupled inductor as shown in Fig. 3.

Besides galvanic isolation, the isolator also serve the purpose of voltage level shifting, or providing multiple outputs [Bla18, Sec. 1.1.1].

However, nonisolated converters are often preferred in applications where galvanic isolation is not a necessity, because they are less bulky, less costly, more efficient and more reliable.

The topic of galvanic isolation can easily occupy an entire course if we really go into the details, but please take advantage of Texas Instruments’ “Introduction to isolation” video series as well as Digi-Key Electronics’ resources [Sch17, Bak18, Pin20].