ABSTRACT
The load impedance varies with different types of loads. Very few loads are truly resistive, as most are either capacitive or inductive. Some loads generate high-current pulses at twice the line frequency or twice the switching frequency, whereas others require high-frequency currents. The load impedance also varies from nearly short to open, depending on whether the rectifier diodes are turned on or off. The most common circuit used is the off-line regulator. Again, this could be with or without the transformer. Power factor correction circuits are an essential aspect of any piece of equipment that has an off-line power supply. There is also a power factor correction coil. In most designs, the electromagnetic interference filter looks very capacitive at the power line frequency, and some specifications demand a near-unity power factor for the filter for two reasons: obviously, for power factor correction, and also for leakage current problems.
