Abstract: A DC-DC converter circuit particularly for use in a photographic flash light emitting device for producing high DC voltage from a low DC voltage such as a battery. Heretofore, the converter transformer of such a circuit has three coils, i.e. a primary coil to be connected to a low DC source, a secondary coil to produce high voltage and a feedback coil for feeding feedback current to the base of a chopping transistor. The purpose of this invention is to eliminate the need for a feedback coil by feeding current from said high voltage in the secondary coil to the base of a transistor.

Abstract: In conventional flash units it is impossible to photograph at a distance which is out of the range of the auto control distance indicator even though proper exposure may be possible due to the latitude of film and error margin in the guide numbers. With the present invention it is possible to photograph either in or beyond the range of the distance auto control with proper exposure.