In Fig.4a, n1 and n2 keep symmetrical, But Q1 is a bipolar and Q2 a MOSFET. The experimental waveforms of I1 and I2
are shown in Fig,4b. Because Q2 is switched faster, it undergoes all the primary current causing by the reverse
recovery process of the output diode, making a spike in the waveform of I2 at the initial moment when Q2 is turned on.
And because Q1 is switched slower, the current flowing through Q2 transfers to Q1 at the moment of being turned off,
causing a spike in I2, and I1 falls to zero with a tail. UA deviates only slightly.