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A diode bridge is an arrangement of four (or more) diodes in a bridge circuit configuration that provides the same polarity of output for either polarity of input. When used in its most common application, for conversion of an alternating current (AC) input into a direct current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a rectifier with a 3-wire input from a transformer with a center-tapped secondary winding. The essential feature of a diode bridge is that the polarity of the output is the same regardless of the polarity at the input. The diode bridge circuit was invented by Polish electrotechnician Karol Pollak 〔(British patent 24398 )〕 and patented on 14 Jan, 1896 under the number DRP 96564. It was later published in Elektronische Zeitung, vol. 25 in 1897 with annotation that German physicist Leo Graetz also was researching this matter at that time.〔Strzelecki, R. (''Power Electronics in Smart Electrical Energy Networks'' ). Springer, 2008, p. 57.〕 Today the circuit is still often referred as Graetz circuit or Graetz bridge. ==Basic operation== According to the conventional model of current flow (originally established by Benjamin Franklin and still followed by most engineers today〔Stutz, Michael (stutz@dsl.org), ("Conventional versus electron flow", ''All About Circuits'', Vol. 1, Chapter 1, 2000. )〕), current is defined to be positive when it flows through electrical conductors from the ''positive'' to the ''negative'' pole. In actuality, free electrons in a conductor nearly always flow from the ''negative'' to the ''positive'' pole. In the vast majority of applications, however, the ''actual'' direction of current flow is irrelevant. Therefore, in the discussion below the conventional model is retained. In the diagrams below, when the input connected to the left corner of the diamond is ''positive'', and the input connected to the right corner is ''negative'', current flows from the ''upper'' supply terminal to the right along the ''red'' (positive) path to the output, and returns to the lower supply terminal via the ''blue'' (negative) path. When the input connected to the left corner is ''negative'', and the input connected to the right corner is ''positive'', current flows from the ''lower'' supply terminal to the right along the ''red'' (positive) path to the output, and returns to the upper supply terminal via the ''blue'' (negative) path.〔Sears, Francis W., Mark W. Zemansky and Hugh D. Young, ''University Physics'', Sixth Ed., Addison-Wesely Publishing Co., Inc., 1982, p. 685.〕 In each case, the upper right output remains positive and lower right output negative. Since this is true whether the input is AC or DC, this circuit not only produces a DC output from an AC input, it can also provide what is sometimes called "reverse polarity protection". That is, it permits normal functioning of DC-powered equipment when batteries have been installed backwards, or when the leads (wires) from a DC power source have been reversed, and protects the equipment from potential damage caused by reverse polarity. Prior to the availability of integrated circuits, a bridge rectifier was constructed from "discrete components", i.e., separate diodes. Since about 1950, a single four-terminal component containing the four diodes connected in a bridge configuration became a standard commercial component and is now available with various voltage and current ratings. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diode bridge」の詳細全文を読む スポンサード リンク
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