To illustrate the function, the engineer will do some circuit analysis. Shown here is the circuit model when the current is freewheeling. From the circuit, Vc=Vn+Ec, and Vn can be calculated from phase A and phase B. From phase A there is one equation, and from phase B there is another. Putting them together, one gets Vn=Ec/2. Therefore, Vn essentially is half the voltage of Vc, which is the back-EMF on the phase C winding.