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3.3. Current limiting

In order to prevent the power supply from being destroyed in an overload condition, the power supply is equipped with a current limitation circuit. Normally, this circuit reduces the primary transistor (one or several) duty cycle while the overload or short-circuit condition remains, and normal operation is regained as soon as the abnormality disappears. Current limitation may have different voltage-current characteristic curves. In most topologies, current limitation in the switching transistor produces an identical output current limitation and it provides an almost rectangular output characteristic curve. In flyback topologies, current limitation in the transistor produces an input power limitation. Foldback limitation is performed by means of circuits that change the current limit as a function of the output voltage. This method is normally used in some linear regulators in order to reduce heat dissipation on the power transistor if an overload condition ari ses.