A DC-DC converter includes an inverter converting a DC supply voltage to a time varying signal. A transformer has a primary winding coupled to the inverter through an LC-tank circuit. A diode structure includes a first diode pair coupled in series between a high-voltage bus and a negative output, and a second diode pair coupled in series between the high-voltage bus and the negative output. The transformer has a secondary winding with a first terminal coupled to a tap between the first diode pair and a second terminal coupled to a tap between the second diode pair. A high-voltage bus transistor selectively couples the high-voltage bus to a positive output in response to a high-voltage bus gate drive signal. A low-voltage bus transistor selectively couples a low-voltage bus at a center tap of the secondary winding to the positive output in response to a low-voltage bus gate drive signal.