Fixed frequency flyback converter

Abstract

A flyback converter including a transformer (T.sub.r), having a primary winding (W.sub.P) and having a secondary winding (W.sub.S), wherein the primary winding is connected in series with a controlled switch (T) and an actuation circuit (A) to an input direct voltage (U.sub.P), and the secondary winding is connected in series with a rectifier (D.sub.S) and, downstream of the secondary winding, a charging capacitor (C.sub.S); the actuation circuit (A) supplies start pulses of a fixed frequency for the switch, has a current sensor (R.sub.P) for the current through the primary winding. Coupled with the secondary winding is a first rectifying amplifier (K.sub.U) for comparing the output voltage (U.sub.S) with an adjustable voltage reference value (U.sub.RefU) and a second rectifying amplifier (K.sub.I) for comparing the output current (I.sub.S) with a adjustable current reference value (U.sub.RefI), wherein as a control signal the combined and decoupled output signals of the two rectifying amplifiers and the output signal of the current sensor of the actuation circuit are supplied for the purpose of influencing the pulse duty radio, the maximum output of the converter-primary part is lower than the product of the output voltage (U.sub.Amax) which can be adjusted to a maximum degree and the output current (I.sub.Amax) which can be adjusted to a maximum degree, the reference values (U.sub.RefU, U.sub.RefI) which can be adjusted to a maximum degree to correspond to the voltage and current values with which the secondary part can be loaded to a maximum, and the level of the control signal (U.sub.S) is limited by a limiter (D.sub.Z), wherein the point (U.sub.Z) at which the limiter is used is selected in such a way that a maximum breaking current in the primary circuit is established corresponding to the maximum permissible power loading of the primary circuit.