At the time moment t2, when the gate-source voltage Vgs(Q21) of the switching element Q22 reaches high, the switching element Q22 is turned on. When the switching element Q22 is turned on, charging of the capacitor C21 starts, the voltage V(N21) at the node N21 starts increasing, and the gate-source voltage Vgs(Q21) of the switching element Q21 also starts increasing.

At the time moment t3, when the voltage V(N21) at the node N21 and the gate-source voltage Vgs(Q21) of the switching element Q21 reach high, the switching element Q21 is turned on.

As shown in FIG. 4, since the rise of the gate-source voltage Vgs(Q21) is delayed from the rise of the gate-source voltage Vgs(Q22), only the switching element Q22 is firstly turned on, while the switching element Q21 remains off. As a result, an excessive voltage may be applied across the drain and source of the switching element Q21, and the switching element Q21 may be broken.

When the switching element Q22 is turned off, the charging of the capacitor C21 stops, and the voltage V(N21) at the node N21 gradually decreases.