Reliable and robust high energy ignition system was optimized and tested for aero piston engine. The traditional fixed-frequency PWM (pulse width modulation) flyback step-up charging method and its drawbacks were analyzed

and then a variable-frequency PFM (pulse frequency modulation) charging method and a way to sense output voltage without resistor arrays feedback were proposed

and the appropriate charge time computation algorithm was presented

lastly the capacitor charge circuit was designed and tested. The experimental result shows that the proposed charging method works correctly with more efficiency

and the charge time computation formula is precise.