Posted on Feb 5, 2014

Each power supply, whether linear or switcher, uses at least two operating modes that characterize its operation: constant voltage (CV) and constant current (CC). The power supply can work in either one, while the other is usually a protective mode, both for the load and for the power supply itself. For example, a constant voltage supply will have

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a protective CC mode and a constant current supply will have a protective CV mode. The protective or limit mode can be designed to: Be designed to limit both output current and voltage, e. g. , as in a power supply with a foldback-type limit feature, maintaining a quasi-constant dissipated power on the power control element. The transitions between these two modes, main operating mode and the protective mode, must be automatic and as smooth as possible. Unfortunately, that is not always the case because of the performance of the supply`s error amplifier. However, this can be corrected by added a Forced Equilibrium Adapter that enables the error amplifier to cope with these operating mode changes. To understand how the Forced Equilibrium Adapter works, we have to first look at the operation of a conventional power supply. Many variable power supplies have a rectangular voltage-current characteristic as shown in Figure 1(a). However, the rectangular characteristic is ideal, and can be applied only for small variations of the output voltage and current, especially near the "CR" point. In reality, the transfer characteristic and the transitions between the two modes, CV and CC, could be represented generically by Figure 1(b). During the transitions between modes, both the amplitude of the transients reached by output voltage and current, along with the duration of the transients, depend on: The characteristics illustrated in...

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