Improvements in or relating to electric power supply apparatus for deriving a relatively high d.c. voltage from a source of relatively low d.c. voltage

摘要

1,021,169. Automatic voltage control. HONEYWELL Inc. Oct. 16, 1964 [Oct.18, 1963], No. 42244/64. Heading G3R. [Also in Divisions H2 and H3] In a D.C. to D.C. converter for charging an electronic-flash capacitor 13, the operation of the transistor oscillator circuit is changed from a relaxation mode of oscillation to a class A mode when the voltage on the capacitor rises above a predetermined level by the inclusion in the oscillator regenerative feedback path of a network 38 whose impedance is changed from a low to a high impedance state in response to the said voltage rise. As shown, the network 38 includes a silicon controlled switch 50 which is normally maintained conducting by a positive voltage on its gate 53. The circuit oscillations generate the gate voltage across a Zener diode 57 and capacitor 60, and generate the switch drive voltage across a capacitor 56. With switch 50 conducting, the network 38 is in its low impedance state and results in the relaxation mode of oscillation in which the core of the oscillator transformer 27 saturates. When the voltage on capacitor 13 reaches a predetermined level, a neon 66 strikes and causes a negative voltage to be applied to the gate 53 of switch 50 to turn the switch off. The network 38 then presents a high impedance to the oscillator regenerative feedback current and results in a low power output class A operation of the oscillator until the voltage on capacitor 13 falls sufficiently for neon 66 to extinguish. The silicon controlled switch 50 may be replaced by a selected silicon controlled rectifier or other known switching element.