Abstract: A step-up DC converter suitable for construction as an integrated circuit chip provides a separate rectangular wave oscillator using a silicon transistor and a power amplifier driven thereby which supplies current to the primary winding of a two-winding step-up transformer matched to the constant duty cycle of the oscillator thereby simplifying construction of the transformer and permitting the oscillator and power amplifier voltage step-up transformer functions to be individually optimized for overall high efficiency operation. A hysteresis switching voltage comparator senses the rectified value of the high voltage output from the transformer relative to a stable reference voltage and switches both the oscillator and the amplifier to their standby current condition when a predetermined high output voltage level is obtained and switches both oscillator and amplifier into conduction when the output voltage falls to a predetermined level.

Abstract: An exposure control circuit that produces a variable exposure interval depending upon scene brightness or a constant exposure interval proportional to a predetermined scene brightness, by providing a photocurrent proportional to the level of actual scene brightness and a reference current proportional to the predetermined scene brightness and, preferably automatically, selectively integrating the photocurrent or the reference current depending upon the relative magnitude of the currents. The integrated current provides a signal to produce a variable exposure interval related to actual scene brightness when the photocurrent is greater than the reference current, or provides a signal to produce a constant exposure interval when the photocurrent is less than the reference current. The selective integration may be disabled to permit only the photocurrent to be integrated over all scene brightness and thus produce an exposure interval related to actual scene brightness beyond the predetermined brightness.