Power Factor is one of the most misunderstood concepts in PSUs. For a more in-depth, technical article read here.
在電源供應器中，必v因數是最容易被誤解的主題之一，這裡有更深入的技術資料。
To understand Power Factor, some basic terms have to be defined.
想要知道必v因數，一些基本單位要先說明定義。
Working Power: This is the power that does some real work, ie. work of heating, lighting and motion.
實央G真正有作用的必v，例如用來發熱、發光、運動等等。
Reactive Power: In order to get a motor moving, the motor must build (and sustain) a magnetic field in the motor coils, which requires power. This power does not "do" anything, but it is required for operation.
虛央G為了讓馬達運轉，馬達得產生(以及維持)一個磁場於線圈中，這需要必v。這時這些必v不能作任何事，但卻是必須的。
Apparent Power is the sum of Working Power and Reactive Power.
視在必v：實孕H及虛左瑭`合。
The formula for Power Factor is Power Factor = Working Power [W] / Apparent Power [VA]. For example if a circuit has a Working Power of 275W and an Apparent Power of 300VA, its Power Factor is 275W / 300VA = 0.92
計算必v因數的公式是 必v因數 = 實?瓦) / 視在必v(VA-伏安)，舉例來說，假使一個電路有275W的實央A300VA的視在必v，其必v因數就是 275W / 300VA = 0.92
The problem with Reactive Power is, that it does not do anything, and is thus not billed by your power company (unless you are an industrial customer, who has to pay additional charges if his power factor is low).
問題就是虛巨S有作用，且不會被電力公司計算進去(除非你是工業用戶，必v因數過低就得另外付錢)
The power company DOES have to provide your household with the Reactive Power, so their generator output must be higher and the grid must be able to take the increased load, overall this costs the power company money. It is also possible that low Power Factor, high-load devices have an effect on the power quality in your house.
電力公司必須要提供"虛?以維持電器用品的運作，所以發電機組必須要有更高的輸出，電力系統也要能承受增加的負荷，這就會花電力公司的錢，也會導致必v因數降低，住家中的高用電裝置便會影響用電品質。
In order to increase Power Factor, passive PFC uses a capacitor in parallel with the AC mains, because the effects of capacitance are exactly opposite those of inductance.
為了增加必v因數，被動PFC把電容並聯於交流電路，因為容抗的影響以及感抗的影響是相對的。
Active PFC uses a special circuit which acts like a resistive load (which has no Reactive Power) and feeds this power to the PSU circuit, isolating it from the mains. One effect this has, is that the overall conversion efficiency is a bit lower, since this circuit inside the PSU consumes power, which is not converted into DC voltage (this is in the range of 3%-8%).
主動PFC使用了特殊的電路，使之有如電阻性負載(電阻性負載不需要虛?並將必v傳送至電源供應器電路，並使之從交流電路隔離，其影響是整體電源轉換效率比較低一點，雖然PFC電路在電源供應器內會耗電，但不會使其直流輸出造成影響(僅於3%~8%)
Overall, you, as end-customer will not directly benefit from PFC. In the long-term it will save you money and problems. Less load on the grid means less likeliness of black-outs. Less load on the power company's generators means that their prices will not go up as fast as they would when they needed to buy bigger generators.
整體來說，身為最終使用者不會直接從PFC電路設計受益，長遠看來將為你省下金錢以及問題，電力系統上較小的負荷也代表跳電次數也會降低，發電廠發電機組負荷較少，代表電費不會因為他們需要更大的發電機組而提高。
In the European Union all power supplies >70W must have either Passive or Active PFC.
歐盟規定所有大於70W的電源都要有被動或是主動PFC。
