| 摘要 |
An alternate approach to meeting the harmonic current limits specified in EN61000-3-2 for power supplies, which fall under the classification of Class A equipment and also provide universal input voltages. In use, an electronic switch(triac) is used as the simple switch between low line input(90-132 VAC) and high line input(180-254 VAC) to provide an auto ranging front end. An inductor is placed in series with the input bridge diodes to increase the conduction angle of the input line current, thereby, increasing the power factor of the supply. This inductor is switched in series with the bulk capacitor whenever the triac is off. In this way, the harmonics are reduced at high line only, and the supply runs unaffected with low power factor at low line. Thus the harmonic currents are reduced at the test voltage of 230V without the need for an active power factor corrective front end.
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