A controller for a DC to DC converter. The controller may comprise linear mode circuitry and switch mode control circuitry. The linear mode control circuitry may be capable of providing a first control signal to a controlled device of the DC to DC converter. The controlled device may operate as a variable resistor in response to the first control signal to control an output voltage of the DC to DC converter. The switch mode control circuitry may be capable of providing a second control signal to the controlled device of the DC to DC converter. The controlled device may turn ON and OFF in response to the second control signal to control the output voltage of the DC to DC converter. One of the linear mode control circuitry and the switch mode control circuitry may be enabled. The controller may also include protection circuitry.