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例2 在图E5-3-1(a)所示电路中,已知VCC=12V,UBE=0.7V,IBQ=40μA,RC=3KΩ,RL=3KΩ,晶体管的输出特性曲线如图E5-3-1(b)所示,试用图解法分析回答下列各问. |
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(1)确定静态工作点ICQ,UCEQ.
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(2)求晶体管的电流放大系数β. |
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(3)若希望IC=1mA,那摸么调整电路元件Rb?
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(4)IBQ=20μA,希望UCEQ=6V,那么RC应该取多少? |
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(5)在(1)条件下,画出交流负载线,并求出失真的最大输出电压幅值,社UCES=0.3V. |
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解 |
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本题的意图是学会用图解法确定静态工作点及进行动态分析. |
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(1)用图解法确定静态工作点ICQ,UCEQ.在输入回路中,输入特性曲线可用UBE=0.7V近似代替,而且有IBQ=40μA.在输入回路中有uCE=Vcc-
iC*Rc,将此直流负载线画在输出特性曲线坐标系中,
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见图E5-3-1(b) |
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与IBQ=40μA的曲线相交于一点Q,此时Q点处的坐标是静态时的集电极电流ICQ,集电极与发射极间电压UCEQ.从图中可得ICQ=2mA,
UCEQ=6V.
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