Power supplies

Claim 1

A power supply including a switching circuit connected to receive a variable supply voltage, the power supply including a ramp generator that produces a ramp output whose amplitude alternates at a fixed frequency and increases gradually from a predetermined value to a second value that varies in response to variations in said variable supply voltage, a trigger circuit connected to control the frequency of the output of said ramp generator, the trigger circuit including a comparator and means supplying an alternating ramp input and a fixed input to said comparator, said comparator providing a trigger output to said ramp generator, the power supply further including a second comparator, means connecting the output of the ramp generator to one input of the second comparator, means supplying a steady signal to another input of the second comparator so that the second comparator provides a pulse output signal in which each pulse is initiated and terminated at transitions of the steady signal and the ramp output so that the pulse width varies in response to variations in said variable supply voltage, and means supplying the variable width pulse output of the second comparator to said switching circuit such that reduction in the supply voltage is compensated for by an increase in pulse width and such that an increase in the supply voltage is compensated for by a decrease in pulse width in such a way that the mean d.c. output of the power supply is substantially independent of variations in the variable supply voltage.