NOVELTY - The converter (200) has a low-side switching MOSFET coupled between a first node and a ground node. A bootstrap capacitor (216) is coupled to a high-side switching MOSFET (202) to provide turn-on voltage for the high-side switching MOSFET. A main refresh circuit is coupled to the bootstrap capacitor, and refreshes the bootstrap capacitor during a first operating mode of the converter. An auxiliary refresh circuit is coupled to the main refresh circuit and the bootstrap capacitor, and refreshes the bootstrap capacitor during a second operating mode of the converter.    USE - Synchronous switching converter e.g. buck converter such as DC/DC buck converter, boost converter and buck-boost converter such as 4-switch buck-boost converter, for use in a charging circuit i.e. integrated circuit (IC) (all claimed), for converting a DC input voltage into a DC output voltage for charging a modern computing device such as desktop computer, laptop computer, tablet computer, portable media player and smartphone, a battery charger and an electrical vehicle. Can also be used as a 2-switch buck-boost converter.    ADVANTAGE - The converter uses an auxiliary bootstrap circuit for refresh operation under light load conditions to prevent negative inductive current. The converter converts the DC input voltage into the DC output voltage for charging the modern computing device, the battery charger and the electrical vehicle without interrupting normal operation.    DETAILED DESCRIPTION - The high-side switching MOSFET and the low-side switching MOSFET are N-type MOSFETs. The first operating mode is a continuous current mode (CCM). The second operating mode is a discontinuous current mode (DCM) and a pulse-frequency modulation (PFM) operation mode. An INDEPENDENT CLAIM is also included for a charging circuit.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of a synchronous switched-mode DC/DC buck converter, which includes an auxiliary bootstrap mechanism.    Synchronous switching converter (200)    Inductor (214)    Bootstrap capacitor (216)    Diodes (220, 240)    Clock gate (228)