An upper bridge circuit is suitable for a switching converter. The upper bridge circuit comprises a first transistor, an upper bridge drive circuit, a capacitor, and an active diode. The first transistor receives a first signal to generate a set signal. The upper bridge drive circuit receives a boost voltage of a boost node and a floating reference voltage of a floating reference node, and controls an upper bridge transistor to supply an input voltage to the floating reference node according to the set signal. The capacitor is coupled between the boost node and the floating reference node. The active diode supplies a supply voltage to the boost node. When the boost voltage is higher than the supply voltage, The active diode isolates the supply voltage from the boost node according to a control voltage. The active diode further comprises a first first type well coupled to the boost node, and the upper bridge drive circuit is located in the first first type well.