Abstract: A DC-to-DC converter is operated in accordance with a predetermined primary circuit ON time and a sensed predetermined secondary circuit current level to provide improved charging performance and extended battery life. Energy is stored in the primary of a coupled inductor when power in the primary, provided by a battery having an internal impedance which varies over the battery's lifetime, is switched ON for a predetermined time t.sub.ON. Upon expiration of time t.sub.ON, power is switched OFF, whereupon stored energy is transferred to the secondary via a flyback type process, thus charging a storage capacitor. A preventing means prevents a premature switching ON of power in the primary subsequent to the expiration of time t.sub.ON. The energy storage cycle repeats when current sensed in the secondary decreases below a predetermined minimum current threshold.

Abstract: In a flyback type self-oscillating DC-to-DC converter, a voltage sensing means indirectly senses the storage capacitor voltage and indicates when the voltage across a storage capacitor has been charged to a predetermined charged value. The voltage sensing means comprises a voltage dividing resistor having a tap intermediate the ends thereof and being connected across a primary winding of a coupled inductor of the DC-to-DC converter. The voltage across the primary winding corresponds to a voltage on the storage capacitor according to the turns ratio of the primary winding to a secondary winding during a measurement period, the measurement period having first and second portions. A comparing means compares a voltage at the tap of the voltage dividing resistor with a predetermined reference voltage and provides an output signal having first and second conditions when the tap voltage is below or above, respectively, the predetermined reference voltage.

Abstract: A flash charge related signal which indicates that there is inadequate flash energy to fire an electronic flash device is provided during flash-charging, until the elapse of a predetermined fraction of the last-measured full charge time for the flash device. The predetermined fraction determines a lesser charge time sufficient to ensure adequate (not full) flash energy for the next flash firing. Thus, the charging time perceived by the photographer always appears shortened to the lesser time, even though the flash device is not fired until it is fully charged. Moreover, the waiting time to fire the flash device can be shortened by relying on the lesser time.