For Rp = 0 the source voltage divides proportional across Lkp and Lm hence the voltage across Lm = V x Lm / ( Lm+Lkp ) = Vm. The induced secondary voltage becomes equal to Ns x Vm / Np. For Rp > zero a voltage drop occurs across Rp. The value of this drop increases in value as the primary current increases with time, hence Vm decrease over time and consequently the secondary voltage declines over time. Thus Rp and magnetizing current contribute to secondary voltage droop. Lkp does not contribute to the droop in the no-load case but does contribute to a lower secondary starting voltage for both the no load and under load cases. Droop is graphically illustrated in Figure 4B. Compare it against the ideal pulse shown in Figure 4A. When a droop is present in the waveform, we do not get the consistent pulse wave amplitude as on the left.
