A buck regulator switching power supply (10) selectively enabling a low side device to effectively recharge a bootstrap capacitor (C_boot) during a high duty cycle of operation. The switching power supply (10) includes a gate driver (12) driving a gate of a high side FET (Q1) responsive to a controller circuit (14). Controller circuit (14) includes a controller (16) responsively controlled by a comparator (18). Comparator (18) senses the charge of the charging side of the bootstrap capacitor (C_boot) as compared to a voltage (V_ref). The comparator (18) also responsively generates an output signal on an output line (20) as a function of the voltage at the phased output.