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An open collector is a common type of output found on many integrated circuits (IC). Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized (open) on a pin of the IC. The emitter of the transistor is connected internally to the ground pin. If the output device is a MOSFET the output is called open drain and it functions in a similar way. == Function == In the picture, the transistor base is labeled "IC output". This is a signal from the internal IC logic to the transistor. This signal controls the transistor switching. The external output is the transistor collector; the transistor forms an interface between the internal IC logic and parts external to the IC. On schematic component symbols, the open output is indicated with these symbols:〔Overview of IEEE Standard 91-1984 Explanation of Logic Symbols〕 * (unicode:⎐) for a pin that outputs low-Z L or hi-Z H (or (unicode:⎒) with an internal pull-up resistor) * (unicode:⎏) for a pin that outputs hi-Z L or low-Z H (or (unicode:⎑) with an internal pull-down resistor) The output forms either an open circuit or a connection to ground. The output usually consists of an external pull-up resistor, which raises the output voltage when the transistor is turned off. When the transistor connected to this resistor is turned on, the output is forced to nearly 0 volts. Open-collector outputs can be useful for analog weighting, summing, limiting, etc., but such applications are not discussed here. A three-state logic device is unlike an open collector device, because it comprises transistors to source and sink current in both logic states, as well as a control to turn off both transistors and isolate the output. 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「Open collector」の詳細全文を読む スポンサード リンク
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