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Electronics-Problems



Second Semester 2018-2019



Problem-1 Determine IC(sat) for the transistor in Figure below. What is the value of IB necessary to produce saturation? What minimum value of VIN is necessary for saturation? Assume VCE(sat) = 0 V. Solution:



𝐼𝐢(π‘ π‘Žπ‘‘) =



𝑉𝐢𝐢 5𝑉 = = 0.5 π‘šπ΄ 𝑅𝐢 10 π‘˜Ξ©



𝐼𝐢(π‘ π‘Žπ‘‘) 0.5 π‘šπ΄ = = 3.33 πœ‡π΄ 𝛽𝐷𝐢 150



𝐼𝐡(π‘šπ‘–π‘›) =



𝐼𝐡(π‘šπ‘–π‘›) =



𝑉𝑖𝑛(π‘šπ‘–π‘›) βˆ’ 𝑉𝐡𝐸 𝑅𝐡



𝑅𝐡 𝐼𝐡(π‘šπ‘–π‘›) = 𝑉𝑖𝑛(π‘šπ‘–π‘›) βˆ’ 0.7𝑉 𝑉𝑖𝑛(π‘šπ‘–π‘›) = 𝑅𝐡 𝐼𝐡(π‘šπ‘–π‘›) + 0.7𝑉 = (1 𝑀Ω) (3.33πœ‡π΄) + 0.7𝑉 = 4.03 𝑉 Problem-2 The transistor in Figure below has a Ξ²DC of 50. -



Determine the value of RB required to ensure saturation when VIN is 5 V.



-



What must VIN be to cut off the transistor? Assume VCE(sat) = 0 V



Solution: 𝐼𝐢(π‘ π‘Žπ‘‘) =



𝑉𝐢𝐢



𝐼𝐡(π‘šπ‘–π‘›) = 𝑅𝐡(π‘šπ‘–π‘›) =



𝑅𝐢



=



𝐼𝐢(π‘ π‘Žπ‘‘) 𝛽𝐷𝐢



15 𝑉 1.2 π‘˜Ξ©



=



= 12.5 π‘šπ΄



12.5 π‘šπ΄ 50



𝑉𝑖𝑛(π‘šπ‘–π‘›) βˆ’ 𝑉𝐡𝐸 𝐼𝐡



=



= 250 πœ‡π΄



5π‘‰βˆ’ 0.7 𝑉 250 πœ‡π΄



= 17.2 π‘˜Ξ©



𝑉𝐼𝑁(π‘π‘’π‘‘π‘œπ‘“π‘“) = 0 𝑉



1



Problem-3 The transistor in Figure below has the following maximum ratings: PD(max) = 800 mW, VCE(max) =15 V, and IC(max) =100 mA. Determine the maximum value to which VCC can be adjusted without exceeding a rating. Which rating would be exceeded first? Solution: First, find IB so that you can determine IC 𝐼𝐡 =



𝑉𝐡𝐡 βˆ’ 𝑉𝐡𝐸 𝑅𝐡



=



5π‘‰βˆ’0.7𝑉 22π‘˜Ξ©



= 195 πœ‡π΄



𝐼𝐢 = 𝛽𝐷𝐢 𝐼𝐡 = (100) (195πœ‡π΄) = 19.5 π‘šπ΄ IC is much less than IC(max) and ideally will not change with VCC. It is determined only by IB and Ξ²DC. The voltage drop across RC is VRC = IC RC = (19.5 mA) (1.0 kΩ) = 19.5 V Now you can determine the value of VCC when VCE = VCE(max) = 15 V VRC = VCC - VCE So,



𝑽π‘ͺπ‘ͺ(π’Žπ’‚π’™) = 𝑽π‘ͺ𝑬(π’Žπ’‚π’™) + 𝑽𝑹π‘ͺ = (πŸπŸ“π‘½) + (πŸπŸ—. πŸ“π‘½) = πŸ‘πŸ’. πŸ“ 𝑽 VCC can be increased to 34.5 V, under the existing conditions, before VCE(max) is exceeded. However, at this point it is not known whether or not PD(max) has been exceeded.



𝑃𝐷 = 𝑉𝐢𝐸(π‘šπ‘Žπ‘₯) 𝐼𝐢 = (15𝑉) (19.5π‘šπ΄) = 293 π‘šπ‘Š Since PD(max) is 800 mW, it is not exceeded when VCC = 34.5 V. So, VCE(max) =15 V is the limiting rating in this case. If the base current is removed causing the transistor to turn off, VCE(max)will be exceeded first because the entire supply voltage, VCC, will be dropped across the transistor.



2



Problem-4 a) For the transistor circuit in Figure below, what is VCE when VIN = 0 V? (b) What minimum value of IB is required to saturate this transistor if Ξ²DC is 200? Neglect VCE(sat). (c) Calculate the maximum value of RB when VIN = 5 V.



Solution: When vin = 0 V, the transistor is in cutoff (acts like an open switch) and



VCE = VCC = 10 V



Since VCE(sat) is neglected (assumed to be 0V), 𝑰π‘ͺ(𝒔𝒂𝒕) = 𝑰𝑩(π’Žπ’Šπ’) =



𝑽π‘ͺπ‘ͺ 𝟏𝟎 𝑽 = = 𝟏𝟎 π’Žπ‘¨ 𝑹π‘ͺ 𝟏 π’Œπ›€



𝑰π‘ͺ(𝒔𝒂𝒕) 𝟏𝟎 π’Žπ‘¨ = = πŸ“πŸŽ 𝝁𝑨 πœ·π‘«π‘ͺ 𝟐𝟎𝟎



This is the value of IB necessary to drive the transistor to the point of saturation. Any further increase in IB will ensure the transistor remains in saturation but there cannot be any further increase in IC. When the transistor is on, VBE β‰ˆ 0.7V. the voltage across RB is



𝑉𝑅𝐡 = 𝑉𝑖𝑛 βˆ’ 𝑉𝐡𝐸 β‰… 5𝑉 βˆ’ 0.7𝑉 = 4.3𝑉 Calculate the maximum value of RB needed to allow a minimum IB of 50 Β΅A using ohm`s law as follows: 𝑹𝑩(π’Žπ’‚π’™) =



𝑽 𝑹𝑩 𝑰𝑩(π’Žπ’Šπ’)



=



3



πŸ’. πŸ‘π‘½ = πŸ–πŸ” π’Œπ›€ πŸ“πŸŽππ‘¨



Problem-5 The LED in Figure below requires 30 mA to emit a sufficient level of light. Therefore, the collector current should be approximately 30 mA. For the following circuit values, determine the amplitude of the square wave input voltage necessary to make sure that the transistor saturates. Use double the minimum value of base current as a safety margin to ensure saturation. VCC = 9 V, VCE(sat) = 0.3 V, RC = 220 Ω, RB = 3.3 k Ω, Ξ²DC =50, and VLED =1.6 V.



Solution: 𝑉𝐢𝐢 βˆ’ 𝑉𝐿𝐸𝐷 βˆ’ 𝑉𝐢𝐸 (π‘ π‘Žπ‘‘)



𝐼𝐢(π‘ π‘Žπ‘‘) =



𝑅𝐢



𝐼𝐡(π‘šπ‘–π‘›) =



𝐼𝐢(π‘ π‘Žπ‘‘) 𝛽𝐷𝐢



=



32.3 π‘šπ΄ 50



=



9 π‘‰βˆ’1.6 π‘‰βˆ’0.3 𝑉 220 π‘˜Ξ©



= 32.3 π‘šπ΄



= 646 πœ‡π΄



To ensure saturation, use twice the value of IB(min), which is 1.29 mA. Use ohm's law to solve for Vin. 𝐼𝐡 =



𝑉𝑅𝐡 𝑅𝐡



=



𝑉𝑖𝑛 βˆ’ 𝑉𝐡𝐸 𝑅𝐡



=



𝑉𝑖𝑛 βˆ’0.7 𝑉 3.3 π‘˜Ξ©



2𝐼𝐡(π‘šπ‘–π‘›) 𝑅𝐡 = 𝑉𝑖𝑛 βˆ’ 0.7𝑉 = (1.29 π‘šπ΄)(3.3π‘˜Ξ©) 𝑉𝑖𝑛 = (1.29 π‘šπ΄)(3.3π‘˜Ξ©) + 0.7𝑉 = 4.96 𝑉



4



Propblem-6 I.



Determine the following dc values for the amplifier in Figure below. (a) IE (b) VE (c) VB (d) IC (e) VC (f) VCE



II.



Determine the following ac values for the amplifier in Figure below. (a) Rin(base) (b) Rin (c) Av (d) Ai (e) Ap



III.



Assume that 600 Ξ©, 12ΞΌV rms a voltage source is driving the amplifier in Figure below. Determine the overall voltage gain by taking into account the attenuation in the base circuit. What is the phase relationship of the collector signal voltage to the base signal voltage?



Solution: I πœ·π‘Ήπ‘¬ ≫ 𝟏𝟎 π‘ΉπŸ π‘‰π‘‘β„Ž = ( 𝑅



𝑅2



1 + 𝑅2



???



) βˆ— 𝑉𝑐𝑐 = 3.66 𝑉



𝑅 βˆ—π‘…



π‘…π‘‘β„Ž = ( 1 2 ) = 9.56 π‘˜Ξ© 𝑅 +𝑅 1



2



|π‘‰π‘‘β„Ž + π‘‰π‘…π‘‘β„Ž + 𝑉𝐡𝐸 + 𝑉𝑅𝐸 | = 0 |π‘‰π‘‘β„Ž + 𝐼𝐡 π‘…π‘‘β„Ž + 𝑉𝐡𝐸 + (𝛽 + 1) 𝐼𝐡 𝑅𝐸 | = 0 𝐼𝐡 =



π‘‰π‘‘β„Ž βˆ’ 𝑉𝐡𝐸 π‘…π‘‘β„Ž + (𝛽+1)𝑅𝐸



= 34.6 πœ‡π΄



𝐼𝐸 = (𝛽 + 1) 𝐼𝐡 = 2.63 π‘šπ΄ 𝑉𝐸 = 𝑉𝑅𝐸 = 𝐼𝐸 βˆ— 𝑅𝐸 = 2.6 𝑉 𝑉𝐡 = 𝑉𝐸 + 𝑉𝐡𝐸 = 3.3 𝑉 𝐼𝐢 = 𝛽 βˆ— 𝐼𝐡 = 2.59 𝑉𝐢𝐸 = 𝑉𝐢𝐢 βˆ’ 𝐼𝐢 𝑅𝐢 βˆ’ 𝐼𝐸 𝑅𝐸 = 6.8 𝑉 𝑉𝐢 = 𝑉𝐢𝐢 βˆ’ 𝐼𝐢 𝑅𝐢 = 9.45 𝑉



5



Note: 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) =



𝑉𝑖𝑛 𝐼𝑖𝑛



=



𝑉𝑏 𝐼𝑏



π‘Žπ‘›π‘‘ 𝑠𝑖𝑛𝑐𝑒 𝐼𝑒 β‰… 𝐼𝑐 ≫≫≫ 𝑉𝑏 = 𝐼𝑒 π‘Ÿπ‘’, 𝐼 𝐼𝑏 β‰… 𝛽 𝑒 π‘Žπ‘



Substituting for Vb and Ib, 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) =



𝑉𝑏 𝐼𝑏



=



𝐼𝑒 π‘Ÿ,𝑒



𝐼𝑒 /π›½π‘Žπ‘



Cancelling Ie, 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) = π›½π‘Žπ‘ π‘Ÿπ‘’,



II 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) = π›½π‘Žπ‘ π‘Ÿπ‘’, = 70 [



25π‘šπ‘‰ 𝐼𝐸



] = 665Ξ©



𝑅𝑖𝑛(π‘‘π‘œπ‘‘π‘Žπ‘™) = 𝑅1 βˆ₯ 𝑅2 βˆ₯ 𝑅𝑖𝑛 (π‘π‘Žπ‘ π‘’) = 622 Ξ© 𝐴𝑣 = 𝐴𝑖 =



𝑅𝐢 βˆ₯ 𝑅𝐿 π‘Ÿπ‘’, 𝐼𝑐 𝐼𝑏



= 261



Note: 𝐴𝑣 =



= π›½π‘Žπ‘ = 70



𝑉𝑐 𝑉𝑏



𝑉𝑐 = π›Όπ‘Žπ‘ 𝐼𝑒 𝑅𝐢 β‰… 𝐼𝑒 𝑅𝐢 𝑉𝑏 = 𝐼𝑒 π‘Ÿπ‘’, 𝐼 𝑅 𝐴𝑣 = 𝐼𝑒 π‘Ÿ ,𝐢 ≫≫≫ 𝐴𝑣 =



𝐴𝑝 = 𝐴𝑣 βˆ— 𝐴𝑖 = 18281



𝑒 𝑒



𝑅𝑐 = 𝑅𝐢 βˆ₯ 𝑅𝐿



III 𝑅𝑖𝑛(π‘‘π‘œπ‘‘π‘Žπ‘™)



𝑉𝑏 = ( 𝑅 +𝑅 𝑠



𝑖𝑛(π‘‘π‘œπ‘‘π‘Žπ‘™)



622 Ξ©



) 𝑉𝑖𝑛 = (600 Ξ©+ 622 Ξ©) 12 πœ‡π‘‰ = 6.1 πœ‡π‘‰



Attenuation of the input network is 𝑅𝑖𝑛(π‘‘π‘œπ‘‘π‘Žπ‘™)



(𝑅 + 𝑅 𝑠



𝑖𝑛(π‘‘π‘œπ‘‘π‘Žπ‘™)



) = 0.51



𝐴,𝑣 = 0.51 βˆ— 261 = 133.6 Vb / Vs



6



𝑅𝐢 π‘Ÿπ‘’,



𝑉𝐢𝐸 = 𝑉𝐢𝐢 βˆ’ 𝐼𝐢 (𝑅𝐢 + 𝑅𝐸 ) Decrease



Increase



Constant



πœƒ = 180π‘œ



7



Propblem-7 Determine the exact voltage gain for the unloaded emitter-follower in Figure below.



Solution: 𝑉𝐡 = ( 𝑅



𝑅2



4.7 π‘˜Ξ©



1 + 𝑅2



𝐼𝐸 = π‘Ÿπ‘’, β‰… 𝐴𝑣 =



𝑉𝐡 βˆ’ 𝑉𝐡𝐸 𝑅𝐸 25π‘šπ‘‰ 1.06 π‘šπ΄ 𝑅𝐸 𝑅𝐸 + π‘Ÿπ‘’,



) 𝑉𝐢𝐢 = (14.7 π‘˜Ξ©) 5.5 𝑉 = 1.76𝑉 =



1.76π‘‰βˆ’0.7𝑉 1.0 π‘˜Ξ©



= 1.06 π‘šπ΄



= 23.6 Ξ© =



1.0 π‘˜Ξ© 1.0 π‘˜Ξ©+23.6 Ξ©



= 0.977



Note: 𝐴𝑣 =



π‘‰π‘œπ‘’π‘‘ 𝑉𝑖𝑛



π‘‰π‘œπ‘’π‘‘ = 𝐼𝑒 𝑅𝑒 𝑉𝑖𝑛 = 𝐼𝑒 (π‘Ÿπ‘’, + 𝑅𝑒 ) 𝐼 𝑅 𝐴𝑣 = 𝐼 (π‘Ÿπ‘’, +𝑒𝑅 ) ≫≫≫ 𝐴𝑣 = 𝑒



𝑒



𝑒



𝑅𝑒 = 𝑅𝐸 βˆ₯ 𝑅𝐿 𝑅𝑒 ≫ π‘Ÿπ‘’, 𝐴𝑣 β‰… 1



8



𝑅𝑒 , π‘Ÿπ‘’ + 𝑅𝑒



Propblem-8 Find the overall current gain Ai in below.



Solution: 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) = π›½π‘Žπ‘1 π›½π‘Žπ‘2 𝑅𝐸 = (150)(100)(1.5 π‘˜Ξ©) = 22.5 𝑀Ω



R in = R1 βˆ₯ R 2 βˆ₯ R in(base) = 33kΞ© βˆ₯ 22kΞ© βˆ₯ 22.5 MΞ© = 13.2 kΞ© Note:



𝐼𝑖𝑛 =



𝑉𝑖𝑛 𝑅𝑖𝑛



=



𝐼𝑖𝑛(π‘π‘Žπ‘ π‘’1) =



1𝑉 13.2 π‘˜Ξ©



= 75.8 πœ‡π΄



𝑉𝑖𝑛 𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’1)



=



1𝑉 22.5 𝑀Ω



= 44.4 𝑛𝐴



𝐼𝑒 β‰… π›½π‘Žπ‘1 π›½π‘Žπ‘2 𝐼𝑖𝑛(π‘π‘Žπ‘ π‘’1) = (150)(100)(44.4𝑛𝐴) = 667πœ‡π΄ 𝐴,𝑖 =



𝐼𝑒 𝐼𝑖𝑛



=



667 πœ‡π΄ 75.8 πœ‡π΄



= 8.8



9



Propblem-9 Find power gain Ap for the unloaded amplifier in Figure below



The same circuit



Solution: 𝑉𝐸 = ( 𝑅



𝑅2



1 + 𝑅2



𝐼𝐸 =



6.8 𝑉 620Ξ©



10π‘˜Ξ©



) 𝑉𝐢𝐢 βˆ’ 𝑉𝐡𝐸 = (32π‘˜Ξ©) 24𝑉 βˆ’ 0.7𝑉 = 6.8𝑉



= 10.97π‘šπ΄



𝑅𝑖𝑛(π‘π‘Žπ‘ π‘’) = π‘Ÿπ‘’, β‰…



𝑨𝒗 =



𝑹π‘ͺ 𝒓,𝒆



=



25 π‘šπ‘‰ 25π‘šπ‘‰ = = 2.28 Ξ© 𝐼𝐸 10.97 π‘šπ΄



𝟏.𝟐 π’Œπ›€ 𝟐.πŸπŸ– 𝛀



Note: 𝐼𝑓 𝑅𝐸 ≫ π‘Ÿπ‘’, , then 𝑅 𝐴𝑣 β‰… π‘ŸπΆ,



= πŸ“πŸπŸ”



𝑒



𝑅𝑐 = 𝑅𝐢 βˆ₯ 𝑅𝐿



𝐴𝑖 β‰… 1 𝑨𝒑 = π‘¨π’Š 𝑨𝒗 β‰… πŸ“πŸπŸ”



10



Propblem-10 For the two-stage, capacitively coupled amplifier in Figure below, find the following values: (a) voltage gain of each stage (b) overall voltage gain (c) Express the gains found in (a) and (b) in dB.



Solution: 𝑉𝐸 = ( 𝑅



𝑅2



8.2π‘˜Ξ©



1 + 𝑅2



𝐼𝐸 =



𝑉𝐸 𝑅𝐸



=



) 𝑉𝐢𝐢 βˆ’ 𝑉𝐡𝐸 = (33π‘˜Ξ©+8.2 kΞ©) 15𝑉 βˆ’ 0.7𝑉 = 2.29𝑉



2.29 𝑉 1.0π‘˜Ξ©



π‘Ÿπ‘’, β‰…



= 2.29π‘šπ΄



25 π‘šπ‘‰ 𝐼𝐸



=



25π‘šπ‘‰ 2.29 π‘šπ΄



= 10.9 Ξ©



R in(2) = R 5 βˆ₯ R 4 βˆ₯ π›½π‘Žπ‘ π‘Ÿπ‘’, = 8.2kΞ© βˆ₯ 33kΞ© βˆ₯ 175(10.9) = 1.48 kΞ© 𝐴𝑣1 =



𝐴𝑣2 =



𝑅𝐢 βˆ₯ 𝑅𝑖𝑛(2) π‘Ÿπ‘’, 𝑅𝐢 π‘Ÿπ‘’,



=



=



3.3 π‘˜Ξ© 10.9 Ξ©



3.3π‘˜Ξ© βˆ₯1.48π‘˜Ξ© 10.9 Ξ©



= 93.6



= 302



A,v = Av1 Av2 = (93.6)(302) = 28267 Av1(dB) = 20log(93.6) = 39.4 dB Av2(dB) = 20log(302) = 49.6 dB A,v(dB) = 20log(28267) = 89 dB



11



Propblem-11 Figure below shows a CE power amplifier in which the collector resistor serves also as the load resistor. Assume Ξ²DC = Ξ²ac = 100, Determinea. The dc Q-point (ICQ and VCEQ). b. The voltage gain and the power gain. c. The power dissipated in the transistor with no load d. the total power from the power supply with no load e. the signal power in the load with a 500mV input



Solution: (a) 𝑉𝐸 = ( 𝑅



𝑅2



330Ξ©



1 + 𝑅2



) 𝑉𝐢𝐢 = (1.0π‘˜Ξ©+330 Ξ©) 15𝑉 = 3.72𝑉



𝑉𝐸 = 𝑉𝐡 βˆ’ 𝑉𝐡𝐸 = 3.72𝑉 βˆ’ 0.7𝑉 = 3.02𝑉 𝐼𝐢𝑄 β‰… 𝐼𝐸 = π‘Ÿπ‘’, β‰…



25 π‘šπ‘‰ 𝐼𝐸



𝑉𝐸 𝑅𝐸1 + 𝑅𝐸2



=



=



25π‘šπ‘‰ 68.3 π‘šπ΄



3.02𝑉 8.2Ξ©+36Ξ©



= 68.3mA



= 0.37 Ξ©



𝑉𝐢𝐸𝑄 = 𝑉𝐢𝐢 βˆ’ (𝐼𝐢 )(𝑅𝐸1 + 𝑅𝐸2 + 𝑅𝐿 ) = 15𝑉 βˆ’ (68.3π‘šπ΄)(8.2Ξ© + 36Ξ© + 100Ξ©) = 5.15𝑉



(b) 𝐴𝑣 =



𝑅𝐿 𝑅𝐸1 + π‘Ÿπ‘’,



=



100 Ξ© 8.2Ξ©+0.37 Ξ©



= 11.7



R in = R1 βˆ₯ R 2 βˆ₯ π›½π‘Žπ‘ (𝑅𝐸1 + π‘Ÿπ‘’, ) = 330Ξ© βˆ₯ 1.0kΞ© βˆ₯ 100(8.2Ξ© + 0.37Ξ©) = 192Ξ© 𝑅



192 Ξ©



𝐴𝑝 = 𝐴2𝑣 ( 𝑖𝑛 ) = 11.72 ( ) = 263 𝑅 100Ξ© 𝐿



The computed voltage and power gains are slightly higher if π‘Ÿπ‘’, 𝑖𝑠 π‘–π‘”π‘›π‘œπ‘Ÿπ‘’π‘‘. (c) If RL is removed, there is no collector current; hence, the power dissipated in the transistor is zero.



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(d) Power is dissipated only in the bias resistor plus a small amount in RE1 and RE2. Since the load resistor has been removed, the base voltage is altered. The base voltage can be found from the Thevenin’s equivalent draw for the bias circuit in figure below 𝑹𝒕𝒉 =



π‘ΉπŸ βˆ— π‘ΉπŸ π‘ΉπŸ + π‘ΉπŸ



= πŸπŸ’πŸ– 𝑽 Rth = 248 V



0.7 V RE1 + RE2 = 44.2 Ξ©



Applying the voltage –divider rule and including the base-emitter diode drop of 0.7 V result in a base voltage of 1.2 V. The power supply current is then computed as 𝑰π‘ͺπ‘ͺ =



𝑽π‘ͺπ‘ͺ βˆ’ 𝟏. 𝟐 𝑽 πŸπŸ“π‘½ βˆ’ 𝟏. πŸπ‘½ = = πŸπŸ‘. πŸ–π’Žπ‘¨ π‘ΉπŸ 𝟏. πŸŽπ’Œπœ΄



Power from the supply is then computed as 𝑷𝑻 = 𝑰π‘ͺπ‘ͺ 𝑽π‘ͺπ‘ͺ = (πŸπŸ‘. πŸ– π’Žπ‘¨)(πŸπŸ“π‘½) = πŸπŸŽπŸ• π’Žπ‘Ύ (e) 𝐴𝑣 = 11.7 π‘½π’Šπ’ = πŸ“πŸŽπŸŽ π’Žπ‘½π’‘βˆ’π’‘ =



π‘½π’‘βˆ’π’‘ πŸβˆ— √𝟐



=



πŸ“πŸŽπŸŽ 𝑽 πŸβˆ— √𝟐



= πŸπŸ•πŸ• π’Žπ‘½π’“π’Žπ’”



π‘‰π‘œπ‘’π‘‘ = 𝐴𝑣 𝑉𝑖𝑛 = (11.7)(177π‘šπ‘‰) = 2.07𝑉 π‘ƒπ‘œπ‘’π‘‘ =



2 π‘‰π‘œπ‘’π‘‘



𝑅𝐿



=



(2.07)2 100Ξ©



= 42.8 π‘šπ‘Š



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Problem-12 For the BJT amplifier of Fig. below, if vin (t) = 0.05 sin (Ο‰t) determine: a) Zi b) Zo c) Av d) Draw the total collector voltage waveform and the total output voltage waveform. Solution: 𝑉𝐡 =



𝑉𝐢𝐢 βˆ— 𝑅2 𝑅1 + 𝑅2



=



15 π‘‰βˆ— (5βˆ— 103 𝛺) 10βˆ—103 𝛺 +5βˆ— 103 𝛺



=5𝑉



𝑉𝐸 = 𝑉𝐡 βˆ’ 𝑉𝐡𝐸 = 5 𝑉 βˆ’ 0.7 𝑉 = 4.3 𝑉 𝐼𝐸 = π‘Ÿπ‘’ =



𝑉𝐸 𝑅𝐸



=



26 π‘šπ‘‰ 𝐼𝐸



4.3 𝑉



= 4.3 π‘šπ΄



1000 𝛺



=



26 π‘šπ‘‰ 4.3 π‘šπ΄



= 6.05 𝛺



𝑅1 βˆ— 𝑅2



𝑅𝐡 = 𝑅1 βˆ₯ 𝑅2 =



𝑅1 + 𝑅2



= 3.33 π‘˜π›Ί



π›½π‘Ÿπ‘’ = 1815 𝛺 𝑍𝑖𝑛 = 𝑅𝐡 βˆ₯ π›½π‘Ÿπ‘’ = 1.12 π‘˜π›Ί π‘π‘œπ‘’π‘‘ = 𝑅𝐢 = 1 π‘˜π›Ί 𝐴𝑣 = βˆ’



𝑅𝐢 π‘Ÿπ‘’



= βˆ’



1000 𝛺 6.05 𝛺



= βˆ’165



π‘‰π‘œπ‘’π‘‘ = 𝐴𝑣 βˆ— 𝑉𝑖𝑛 = βˆ’ (165) βˆ— (0.05) 𝑠𝑖𝑛 (πœ”π‘‘) = βˆ’8.25 𝑠𝑖𝑛 (πœ”π‘‘)



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