Abstract: An inverter circuit charges a capacitive load 4 incrementally by repetitive fly-back in an inductor 8 connected in series with an FET 9 across DC input terminals 2,3. A transistor 14, turned ON in response to current build-up in the inductor 8 during each charging cycle, switches FET 9 OFF to initiate fly-back, and feedback from the fly-back acts via a resistor 16 to hold transistor 14 ON and FET 9 OFF through to the cycle end. Adding resistors 21,22 in series with the load 4 across the input terminals 2,3, derives a voltage which, like that via the feedback resistor 16, is dependent on the input voltage. The derived voltage acts via a zener diode 23 to counteract the feedback, holding transistor 14 OFF and interrupting further charging until the load 4 is discharged into a xenon flash-tube 5. By making the values of resistors 16 and 21 equal, the load 4 charges to a voltage independent of input-voltage variation; with them unequal, a deliberate variation of output voltage with input can be obtained.