Abstract: In dental x-ray apparatus a control is provided for driving the high voltage transformer in the tube head at a frequency far above power line frequency. The transformer is driven with an inverter. A precision d-c voltage regulator that operates in an "add-on" mode and thus only handles a portion of the output current controls the voltage supplied to the inverter. The d-c voltage regulator is supplied a voltage by a transformerless a-c/d-c converter whose output is proportional to the 60 Hz power line voltage that supplies it. The x-ray tube filament transformer is also driven at a frequency above power line frequency. Means are provided to cut off power to the x-ray tube if its current does not reach a certain value within a short time after an exposure is initiated. Means are provided for isolating high voltage power circuits from low voltage control circuits.