Dynamic and Static Cross Regulation in Forward Converters

Many power supplies are described as multi-output, in which one switching power stage is used to derive several outputs. Often these power supplies are constructed with one output being fed back and while the controlled output may have excellent regulation characteristics, the other outputs are only semiregulated. A topic of interest to designers of such power supplies is the cross regulation performance which is defined as the response of the semiregulated output to a load disturbance on the regulated output. The semiregulated outputs often experience large variations due to load changes and these may make it difficult to meet the specified regulation requirements. In this paper, an analysis is presented leading to equations that can predict the cross regulation performance of converters that have coupled or uncoupled output inductors. The predicted results compare very well with measurements made on a three output converter. In addition, a model suitable for simulation is developed to simulate the cross regulation performance, and the simulation results also agree with the measurements and the predicted performance.