Capacitors, Magnetic Circuits, and Transformers is a free introductory textbook on the physics of capacitors, coils, and transformers. See the editorial for more information....

Power Output

It should be emphasized that IL represents the average value of one-half of the load current wave. However, in expressing the power expended in a resistance, the square of the effective value of the current is multiplied by the value of the resistance. The ratio of effective to average value of a periodic current or voltage is called the form factor kf, which is 1.11 for a sinusoid. The effective value of the load current is therefore

and if the load resistance is RL ohms, the output is


For a given a-c source voltage V, the output current is a maximum when α = 0, and, if the leakage reactance is neglected, the maximum output current is


where R'G is the resistance of the gate circuit, which, in the case of the parallel connection, is the resistance of each gate winding, and for the series connection is twice the resistance of each gate winding. The a-c source voltage is assumed to be sinusoidal; therefore, the output current is sinusoidal when α = 0 and kf = 1.11. The maximum power output is, therefore, approximately


Form factor

When the leakage impedance of the gate windings is neglected, the average value of the output current to a noninductive load resistance is expressed by Eq. 7-25, as follows


The effective rms value of the load current is


and the form factor is the ratio of Eq. 7-32 to Eq. 7-31. This ratio can be reduced to


Last Update: 2011-01-13