D.C. to d.c. converter with plural feedback loops

Claim 1

A d.c. to d.c. converter for deriving from a relatively low voltage battery supply a relatively high voltage d.c. output, comprising: a step up transformer having means defining primary and secondary windings; oscillator means for producing an output which oscillates between first and second states; semiconductor switching means controlled by said oscillator output to switch on and off in response to said first and second states, respectively, said switching means being arranged to switch current flowing through the transformer primary in such a manner that upon switching on of the switching means the current builds up progressively and upon switching off of said switching means the current changes abruptly in a manner to induce a relatively high voltage pulse in said secondary winding and such that there is formed in said primary winding a relatively low flyback voltage pulse of a magnitude which is a function of the magnitude of said high voltage pulse; output means coupled to the secondary winding and arranged to derive said high voltage d.c. output from high voltage pulses induced in the secondary winding; first control means for controlling the frequency of oscillation of the oscillator in dependence upon the magnitude of said low flyback voltage pulse formed in the primary winding; second control means including sensing means for sensing the magnitude of the current building up in the primary; means for causing the oscillator output to change from said first to said second state when the current level sensed by said sensing means exceeds a given level; and third control means for sensing an abnormal load condition on said high voltage d.c. output and controlling the oscillation frequency of said oscillator means in accordance therewith.