Small-Signal or AC Solutions (a) Redraw the circuit with V+ = V−=0and all capacitors replaced with short circuits as shown in Fig. In the common-emitter section of this chapter, we saw a SPICE analysis where the output waveform resembled a half-wave rectified shape: only half of the input waveform was reproduced, with the other half being completely cut off. Substituting r e equivalent circuit, note that: R E is absent due to the low impedance of the bypass capacitor C E. When V CC is set to zero, one end of R 1 and R C are connected to ground. For a BJT, the common base current gain α = 0.98 and the collector base junction reverse bias saturation current, I CO = 0.6 µA. 12/3/2004 Steps for DC Analysis of BJT Circuits 6/11 Jim Stiles The Univ. of EECS But think about what this means! Why? This BJT is connected in the common emitter mode and operated in the active region with a base current (I B) of 20 µA.The collector current I C for this mode of operation is Step 2: Solve the circuit to find IC, IB, and VCE. (15 Points). the best biasing circuit for BJT is voltage divider bias ... BJT transistor solved problems on interacting diode junctions and is applicable to all the transistor operating modes Option (d) Two Marks Questions 1. Electronic Problems Second Semester 2018-2019 Problem-1 Determine the following for the fixed-bias … Find the bias point of the transistor (Si BJT with β = 100 and VA → ∞). If so the solution is complete; Ask Question Asked 3 years ago. Since our purpose at that time was to reproduce the entire waveshape, this constituted a problem. Step 3: Check to see if the values found in Step 2 are consistent with the assumed operating state. 30k 20k 2.5 V 500 500 12k 1.5 V R 1 and R 2 remain part of the input circuit while R View BJT-BIAS- Problems _ Solutions.pdf from EEE 489 at Walden University. The collector current ¼ for this mode of operation is (a) 0.98 mA (b) 0.99 mA BJT AC Analysis Voltage Divider Bias As shown in the figure, it is the voltage divider bias configuration. Explanation: To obtain an approximate answer, under saturation the BJT is ON and hence acts as a short circuit. For an exact answer, if the BJT is a Silicon transistor, then drop V CE = 0.2V and current is 12-0.2/2.2=5.36 mA. If we find one unknown voltage, we can immediately determine the other. 4.5 Large - Signal DC Analysis of BJT Circuits Step 1: Assume an operation region for the BJT and replace it by the corresponding large signal equivalent circuit. Explain The Operation Of Npn BJT Transistor By Taking Into Account Biasing Of Base-emitter As Well As Base-collector Junctions. (b) Calculate gm, rπ, re,andr0 from the DC solution.. gm= IC VT rπ= VT IB re= VT IE r0 = VA+VCE IC (c) Replace the circuits looking out of the base and emitter with Thévenin equivalent circuits biasing is the process of maintaining the transistor in active or linear region so that it can ready to amplify the small signal applied. Therefore, a D.C. analysis problem for a BJT operating in the active region reduces to: find one of these values , , B C E ii ori 4.6 Solution to Selected Exercise Problems Problem 1. Please Also State The Connection Between The Operation Of Pop And Npn Transistors. 3. Emitter-Bias Configuration •Improved bias stability (check example 4.5) 12 ECE-Lec#3 4 The addition of the emitter resistor to the dc bias of the BJT provides improved stability, that is, the dc bias currents and voltages remain closer to where they were set by the circuit when outside conditions, such as temperature and transistor beta, change. 9. However, ideally a drop exists for the transistor which is a fixed value. Biasing of CE amplifier with emitter resistor for specific gain. ... Voltage divider bias (BJT) leads to a huge voltage drop across the collector resistor. ... finding Ic with two opposite voltages connected to base. Figure 2: DC bias circuit. This BJT is connected in the common emitter mode and operated in the active region with a base drive current »=20 . Figure 3: Signal circuit. 1. of Kansas Dept. 1. BJT Voltage Divider Bias Circuit problem. For a BJT, the common – base current gain =0.98 and the collector base junction reverse bias saturation current ¼0=0.6 .