# Dot Convention **Convention for denoting the relative instantaneous polarities of [[Inductance#Mutual inductance|magnetically coupled]] [[Inductor|inductors]].** Dot convention is required to specify the relative winding directions of inductors. A current *entering* the dotted terminal of one coil produces a *positively sensed* voltage at the dotted terminal of the second coil. ![[DotConvention.svg]] Note that the value of $v_{2}$ is taken with respect to *how it is defined on the diagram*, as in with the positive terminal on the top. Additionally, $i_{2}$ has been shown to indicate the flow of current in the right loop if it is *completely driven* by the mutual inductance. ## Inductors in series > For magnetically coupled coils in series, where the dots are on the *same side* of both inductors, the connection is called *series-aiding*. > $L_{\text{eq}}=L_{1}+L_{2}+2M$ > ![[DotConventionSeriesAiding.svg|550]] > The opposite case is known as a *series-opposing* connection. > $L_{\text{eq}}=L_1+L_2-2M$ > ![[DotConventionSeriesOpposing.svg|600]] ## Inductors in parallel > For magnetically coupled coils in parallel, if the dots are on the *same side*, > $L_\text{eq}=\frac{L_{1}L_{2}-M^{2}}{L_{1}+L_{2}-2M}$ > ![[DotConventionParallelSame.svg|400]] > If the dots are on *opposite sides*, > $L_\text{eq}=\frac{L_{1}L_{2}-M^{2}}{L_{1}+L_{2}+2M}$ > ![[DotConventionParallelOpposite.svg|400]]