A switched mode assisted linear regulator includes a linear amplifier (LA) and a buck converter configured as a current source. In example embodiments, the buck converter circuit includes a power switch M1 with an M1 body diode (tub), and includes buck turn-off circuitry configured to avoid negative inductor current by controlled switching of the tub to the higher of VIN and a second voltage. For DC-coupled configurations, boost functionality is provided by an LA boost supply, and the tub is switched to the boost supply. For AC-coupled configurations, boost functionality can be provided without boosting the LA supply rail by constraining signal peak-to-peak amplitude to be less than the LA supply voltage (maintaining a DC-average voltage on the AC-coupling capacitor), and the tub is switched to the higher of VIN and VOUT. The buck turn-off circuitry can include zero crossing detection to control M1 tub switches.