AC-DC converter triggered by variable frequency pulses

Claim 1

A circuit arrangement for forming a direct voltage from an essentially sinusoidal input voltage comprising: a filter for suppressing high-frequency interference signals, a switched mode power supply which includes a diode, a coil, a capacitor and a transistor and is coupled to the filter through a rectifier, the power supply elements being connected so that in the conductive state of the transistor the diode is cut off and coil current flows at least through the transistor and in the cut-off state the current flows through the diode and a parallel arrangement of a load and the capacitor, and a pulse generator responsive to the input voltage to form switching pulses for the transistor whose frequency is varied uniformly in time between a minimum frequency at a maximum value of the rectified input voltage and a maximum frequency at the minimum value, characterized in that the pulse generator comprises, a voltage-to-frequency converter responsive to the input voltage to form starting pulses which determine the beginning of the switching pulses and whose frequency is varied between the minimum and maximum values such that the second derivative of the frequency with respect to time is always zero or negative, a first integrator which produces an integrated output signal proportional to the output current of the rectifier and whose time constant is larger than the reciprocal value of the minimum frequency, a superposition circuit forming an output signal equal to the difference between a signal proportional to the rectified input voltage and the output signal of the first integrator, and a first comparison circuit which produces a signal for terminating a switching pulse when a signal proportional to the output current of the rectifier exceeds the output signal of the superposition circuit.