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发表于 2012-11-6 22:39:26
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本帖最后由 475627406 于 2012-11-6 22:40 编辑
Switching Power Supplies A to Z 中有如下的描述
But whenever we switch the transistor, we effectively disconnect the input from the output (during either the ON or OFF state). However, the output (load) always demands a continuous flow of energy. Therefore we need to introduce energy storage elements somewhere inside the converter. In particular, we use output capacitors to “hold” the voltage steady across the load during the above-mentioned input-to-output “disconnect” interval.
But as soon as we put in a capacitor, we now also need to limit the inrush current into it — all capacitors connected directly across a dc source, will exhibit this uncontrolled inrush — and that can’t be good either for noise, EMI, or for efficiency. Of course we could simply opt for a resistor to subdue this inrush, and that in fact was the approach behind the early “bucket regulators” (Figure 1-2).
But unfortunately a resistor always dissipates — so what we may have saved in terms of switch dissipation, may ultimately end up in the resistor! To maximize the overall efficiency, we therefore need to use only reactive elements in the conversion process. Reactive elements can store energy but do not dissipate any (in principle). Therefore, an inductor becomes our final choice (along with the capacitor), based on its ability to non-dissipatively limit the (rate of rise) of current, as is desired for the purpose of limiting the capacitor inrush current.
书中讲到图中的电容是保持电压稳定
而电感是防止电容充电电流突变 |
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