Dot convention

In circuit analysis, the dot convention is a convention used to denote the voltage polarity of two mutually inductive components, such as winding on a transformer.

The polarity of all dotted terminals will be the same at any particular time, assuming an ideal transformer with no leakage inductance.

When the current in a loop enters the dot, then positive voltage is induced at the dot of the other loop. Alternately, when current in a loop leaves the dot, negative voltage is induced at the dot of the other loop. Similarly if two inductors are in series the dot convention can be used in the same manner as in case of transformer.

Sinusoidal AC

For sinusoidal AC such as the mains, the convention can be thought of in either of the following ways:

1. The current going into one dot (either dot) "tries" to come out the other dot. "Into" meaning from the dot toward the inductor, and conversely "out" meaning from the inductor d the dot.
2. Current going into a dotted terminal of the inductor induces a positive voltage at the other dot. Conversely, current leaving a dotted terminal induces a negative voltage at the other dot.

See also

• Electrical polarity