An inverter receives a d.c. voltage and delivers to an X-ray tube, by way of a high-voltage transformer, filter, and rectifier, a high-voltage d.c. output. The inverter is driven in response to control signals which are responsive to the difference between a voltage demand signal and a voltage feedback signal. The control signals are also responsive to various status conditions of the system which are monitored by a microprocessor. Inputs to the microprocessor include various signals which are indicative of voltage or current conditions. In this way, such conditions as an over-voltage at the output, an unbalance between the anode and cathode with respect to ground, or an excessive current flow are detected and precautionary measures are quickly taken to prevent further damage to the system.