A ballast circuit for a high intensity discharge lamp includes a boost converter, responsive to a dc input voltage, for providing a boosted dc output voltage; a boost controller, responsive to the boosted dc output voltage, for driving the boost converter to maintain the boosted output voltage at a predetermined level; a buck converter, responsive to the boosted dc output voltage, for providing a reduced dc output voltage; and a buck controller, responsive to the reduced output voltage, for driving the buck converter to operate the discharge lamp in a transition mode and maintaining the reduced dc output voltage at a preselected level for operating the discharge lamp in a steady state mode.