Method and device to accurately regulate the input symmetry of a push-pull converter by large variations of the input voltage

摘要

1. Method for maintaining the input symmetry of a push-pull inverter subject to large fluctuations of the input voltage as well as the output load, whereby the deviation from norm is formed from the output voltage or the output current as the actual value of the norm size and the desired value and the actual value is held constant by varying the switching times of transistors periodically switched on and off, which alternately control the flow of primary currents in a transformer of the push-pull inverter and whereby the current carrying periods of the transistors are measured and differences are derived from the measuring values, especially from the amplitudes of the currents flowing over the transistors (34, 36), said differences corresponding to the asymmetry of the primary currents and acting upon servo components for the setting of the same primary currents characterised in that the current amplitudes or the voltage time surfaces of the currents or voltages present in the transistors (34, 36) in every current carrying period are measured and that when the voltage time surfaces or current amplitude in one current carrying period of the first transistor (34) has been ascertained, the difference is formed by use of the voltage time surface or current amplitude of the directly previous current carrying period of the second transistor and the deviation from norm, until a further difference can be given at the measuring of the following amplitude or voltage time surface, is switched up in this sense to influence the length of the current carrying period of the first transistor (34), that the period is lengthened when the voltage time surface or the current amplitude on the second transistor (36) exceeds that of the first transistor and is shortened in the reverse case.