Control algorithms and circuit designs for optimal flyback-charging of an energy-storage capacitor (e.g., for flash lamp or defibrillator)

A flyback-type of a transformer-coupled DC/DC power converter supplies a train of current pulses to charge an energy-storage capacitor to a desired high voltage, converting input DC power obtained from a lower voltage DC source. The energy-storage capacitor is charged to a specified voltage within a specified time with minimum peak and RMS currents in the transistor, the rectifier diode, the transformer windings and the DC power source, minimizing the i²R losses. This is done by generating: (1) energy-storage current pulses in the power transistor and the transformer primary winding in which the current increment from the beginning to the end of a pulse is only a small fraction of the final (peak) value; and (2) energy-delivery flyback current pulses in the capacitor and the transformer secondary winding in which the current decrement from the beginning to the end of a pulse is only a small fraction of the initial (peak) value. Recommended methods are: (1) hysteretic current-mode control with current sensing in both transformer windings; (2) peak-current-commanding current-mode control with switching frequency or transistor-nonconducting time varying in a prescribed way during the charging; or (3) valley-current-commanding current-mode control with switching frequency or transistor-conducting time varying in a prescribed way during the charging. Compared with one nonoptimal method, peak currents are reduced by a factor of about 2 and i²R power losses are reduced by a factor of about 1.33