For a buck-boost DC-DC converter with n-type high-side field effect transistor (HSFET), a supply is derived from input and output rails, and this supply maintains a constant differential voltage independent of input supply voltage. The derived supply is used as the high supply (HS) of an HSFET Driver. As such, the HSFET resistance becomes independent of supply variation. A wide range ultra-low IQ (Quiescent current), edge triggered level-shifter provides support to a bootstrapped power stage of the inverting buck-boost DC-DC converter. When p-type HSFET is used, a supply is derived from the input and output supply rails, and this derived supply maintains a constant differential voltage independent to the input supply voltage. The derived supply is used as the low supply (LS) or ‘ground’ of the HSFET Driver. As such, the p-type HSFET resistance becomes independent of supply variation.