[電路圖] http://www.wretch.cc/album/show.php?i=fairwarning&b=73&f=1071601559&p=0 [題目] An ideal OPA is connected as shown in the Fig. The transistor has a very high β and Vcc=15V If Vi=-5V , choose the correct Vo from the following answers: -5V,-8V,-10V,-15V,5V,8V,10V,15V,0V,none of the above. [解答] Vi=-5V: 設BJT截止..則Vo=15V (由OPA的"-"端為0V...可知BJT的確為截止) 經過計算..我是覺得的確是在截止區.. 但括號內說:由OPA的"-"端為0V...可知BJT的確為截止... 請問..上述的話要怎麼判斷呢? "由OPA的"-"端為0V"............我看不來耶...= = 因為對這句不太懂..感覺是我的觀念出了錯.. 可以請大家幫忙糾正/釐清我的想法嗎? 謝謝大家的熱心~~ -- 吉他演奏曲 http://blog.xuite.net/iloveguitar/music?st=c&re=list&p=1&w=641095 --

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