A soft hybrid-electric vehicle power supply circuit (14) is provided. The circuit includes a load sensor (19), which generates a load signal. A high-voltage bus (26) supplies a high voltage for a high-voltage load (30) and a low-voltage bus (28) is electrically coupled to and supplying a low-voltage to a low-voltage load (32). A converter circuit (24) is electrically coupled to the high-voltage bus (26), the low-voltage bus (28), and a high-voltage load (30). The converter circuit (24) maintains a predetermined minimum voltage level on the high-voltage load (30) by switching between the high-voltage bus (26) and the low-voltage bus (28) in response to the load signal. A method of maintaining the predetermined minimum voltage level is also provided.