The Trailing Edge
For an ideal pulse transformer, once the primary switch is opened the secondary pulse should immediately end. This does not happen. The pulse transformer tries to dissipate the energy stored in Lm and in the parasitic components Cp, Cs, Lkp, and Lks. The inductance will induce voltages as their magnetic fields collapse. The capacitor charge will drain, but will not drain instantaneously. The capacitances may temporarily supply current to the inductances. As a result, there is a sloped decline of the secondary output voltage after the primary switch is opened. This sloped decline is referred to as the trailing edge. Some combinations of capacitance and inductance could produce spurious oscillations (known as ringing). A trailing edge is graphically illustrated in Figure 6B below.