[电路图] http://www.wretch.cc/album/show.php?i=fairwarning&b=73&f=1071601559&p=0 [题目] 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: 设BJT截止..则Vo=15V (由OPA的"-"端为0V...可知BJT的确为截止) 经过计算..我是觉得的确是在截止区.. 但括号内说:由OPA的"-"端为0V...可知BJT的确为截止... 请问..上述的话要怎麽判断呢? "由OPA的"-"端为0V"............我看不来耶...= = 因为对这句不太懂..感觉是我的观念出了错.. 可以请大家帮忙纠正/厘清我的想法吗? 谢谢大家的热心~~ -- 吉他演奏曲 http://blog.xuite.net/iloveguitar/music?st=c&re=list&p=1&w=641095 --

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