已知BJT在Q点上的30，试求

1、IBQ = 12/300 = 0.04 mA；ICQ =βIBQ = 30 * 0.04 = 1.2 mA;UCEQ = 12 - 1.2 * 4 = 6.2v 。2、Av = ( βRL//Rc )/(Rb//Rbe ) = 30 * 2000/850 = 713、Ri =Rb//Rbe≈Rbe = 200 + 26/0.04 = 850Ω4、Ro =RL//Rc = 4//4 = 2 kΩ；5、电路无任何稳定工作点措施，所以工作点不稳定。例如电压变化，电流会随之变化 。