4.32 Write B-E loop and C-E loop B-E loop VBB = IBRBB + VBE +IERE IE =2.09 mA C-E loop VCC = ICRC + VCE +IERE VCE =4.8 V This is how all DC circuits are analyzed and designed! C-E loop B-E loopĮxercise 4.24 (a) Find VC, VB, and VE, given: b = 100, VA = 100V IE = 1 mA IB IE/b= 0.01mA VB = 0 - IB10K = -0.1V VE = VB - VBE = -0.1 - 0.7 = -0.8V VC = 10V - IC8K = 10 - 1(8) = 2V VB RBB is measured with voltage sources grounded.Use the Thevenin equivalent circuit for the base.2mA = 9 /(RB1 + RB2) AND VB = VCC 3 = 9, Solve for RB1 and RB2. Make the current in the voltage divider about 10 times IB to simplify the analysis.Use a voltage divider, RB1 and RB2 to bias VB to avoid two power supplies.ac input signalĤ.6 Analysis of transistor circuits at DC For all circuits: assume transistor operates in linear region write B-E voltage loop write C-E voltage loop Example 4.2 B-E junction acts like a diode VE = VB - VBE = 4V - 0.7V = 3.3V IC IE = (VE - 0)/RE = 3.3/3.3K = 1mA IC IE = 1mA VC = 10 - ICRC = 10 - 1(4.7) = 5.3V IEĮxample 4.6 B-E Voltage loop 5 = IBRB + VBE, solve forIB IB = (5 - VBE)/RB = (5-.7)/100k = 0.043mA IC= bIB = (100)0.043mA = 4.3mA VC = 10 - ICRC = 10 - 4.3(2) = 1.4V b = 100 IC IB IEĮxercise 4.8 VE = 0. (DC input signal 0.7V) The slope of the ic - vBE curve at the bias point Q is the transconductance gm: the amount of ac current produced by an ac voltage. It gives rise to a collector signal current ic, superimposed on the dc current IC. Transconductance IB ac output signal DC output signal A small ac signal vbe is superimposed on the DC voltage VBE. A transistor’s operating point (Q-point) is defined by.We must operate the transistor in the linear region.Slope of output characteristics in linear region is near 0 (scale exaggerated).At a fixed IB, IC is not dependent on VCE.Output characteristics IC IB = 40mA IC IB = 30mA IB = 20mA IB = 10mA VCE Early voltage Cutoff region Summary of equations for a BJT IE IC IC=bIB b is the current gain of the transistor 100 VBE = 0.7V(npn) VBE = -0.7V(pnp)Ĥ.5 Graphical representation of transistor characteristics IC IB Output circuit Input circuit IE Summary of pnp transistor behavior pnp IC collector base large current IB + VBE - emitter IE small current Summary of npn transistor behavior npn IC collector base large current IB + VBE - emitter IE small current Modes of operation of a BJT transistor Mode BE junction BC junction cutoff reverse biased reverse biased linear(active) forward biased reverse biased saturation forward biased forward biased Operation of npn transistor Large current
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