Paper , Order, or Assignment Requirements

Wire the circuit  shown, with R_c = 470 Ω  and Q =  2N3904

• Record I_band I_c  in the table below for the given values of R_B

RB	Ib	Ic	Vbe	Vce	Beta
1MΩ
470KΩ
200KΩ
100KΩ
47KΩ

• Return the R_B value to 470KΩ,

(A) Squeeze the transistor between your fingers to raise the case temperature, record any change in collector current  _______

(B)  Put a piece of ice in a plastic bag and hold it on the transistor to reduce the case temperature, record any change in collector current __________

• Describe your perception of  the relationship between Beta and case temperature.
• Describe the behavior of Beta vs I_c

Written Assignment 4

Answer all of the following questions/problems and submit them to your mentor.

Questions:

1. In a transistor circuit, the two extreme ends of the loadline are called:
2. When used as an amplifier, the transistor is usually biased in the region called the _______________ region.
3. The Q  point for an amplifier  is identified as _______ & _______ , which together determine the power dissipated  in the transistor.

Problems:

1. For the circuit shown,  V_BB= +10v,  V_cc = +30v, R_B = 470kΩ, R_c = 6kΩ  Calculate the operating point for the circuit shown for a Beta value of 90 and for a Beta value of 130.

2. For the circuit shown,  V_cc= -10v, R₁ = 10kΩ,  R₂ = 2.2kΩ,   R_c = 3.6kΩ, R_E = 1kΩ.  Calculate the operating point for the circuit shown.  Use I_B = I_C / Beta and calculate I_B for Beta = 90.

Module 4 Lab: AC Riding on DC

R₁ = 2.2KΩ    R₂ = 4.7KΩ   C = 0.1uF   V_dc =  +5v  V_ac = 3v peak  f = 1KHz

• Use superposition to calculate the  DC  voltage at  point X     V_DC=  ______
• Use superposition to calculate the  AC  (peak)  voltage at  point X     V_AC=  ______

• Sketch what you think the scope will show at X:

• Wire the circuit and connect a scope probe at X, be sure to DC couple the input and set the ground level at the bottom of the scope display, then sketch the results.

Written Assignment 5

Answer all of the following questions/problems and submit them to your mentor.

Questions:

1. Describe what is meant by the voltage gain of an amplifier.
2. What is the primary purpose of coupling capacitors in transistor amplifiers?

Problems:

1. If  the input voltage to an amplifier is  50mV and the resulting output voltage is 3V, calculate the voltage gain.

2. A transistor is biased with  I_E= 5mA.     Calculate r’_e
3. For the circuit shown, calculate:
   1. The input resistance at the base of the transistor.
   2. The input resistance of the amplifier.
   3. The voltage gain.

4. If a circuit requires a capacitor to give good coupling at 200Hz and the resistance the capacitor is connected to is  3Kohms,  what value capacitor is needed?

Module 5 Lab: Amplifier Gain and Comparing Constant Bias to VDB

Part I

(A) Wire the circuit shown. [ you will determine the β value from DC measurements]

R₁ =  20KΩ,  R₂ = 5MΩ  ( two 10MΩ in parallel ),  R₃ = 20KΩ, C = 0.1uF, use 2N3904 for the transistor

• Measure  D.C.    V_c=  _____   and  V_be = _____

• Calculate I_c= ( V_cc –  V_c )/ R_c = ______      and I_B = ( V_cc –  V_be )/ R_B =  _____    then β =  _____

(a)  Verify that R_be = R_{in base} = β r_e^’

• Measure A.C. voltages   v_c= ____   v_be =  _____

• Calculate i_b= ( 10mV – v_be ) / 20 Kohms = _____

• Calculate i_c= v_c / 20kΩ = _____  calculate β_ac = i_c / i_b = ______

• R_be= v_be / i_b = _____     r_e^’ = 25mV/ I_E   =  _______   i_c = β_ac i_b = ____

• Also calculate  R_be= β_ac r_e^’ = _____  does this check with the value above?

(B)  To show the effects of changing beta on the Q point.

• Hold your finger on the case to raise the temperature and the Q point should change (V_cgoes down) due to the fact that beta goes up as temperature goes up causing an increase in  I_c.
• With a piece of ice in plastic bag, hold it on the transistor to cool it; this should cause beta to decrease.  The Q point will change again ( V_cgoes up ).

Part II

To show the  advantage of VDB over CCB

• Wire the VDB circuit shown. The transistor beta value was determined in part A.

• Measure [ D.C.]    V_B= ____  and  V_E = _____

• Calculate I_E=  _____               and  r_e^’  =  _____

• Measure [ A.C. ]    v_in=  _____   and  v_o = ____

• Now calculate voltage gain by two methods:

• A_v=  v_c / v_in =  ______    and A_v =  R_c / r_e^’ =   _______.

• Do these two values match?

• Next hold your finger on the transistor and notice that the Q point does not change.  Change the transistor and again note that the Q point stays constant.

Written Assignment 6

Answer all of the following questions/problems and submit them to your mentor.

Questions:

1. For each circuit shown, indicate if it is CE, CB or CC amplifier.

Figure A

Figure B

Figure C

2. Show two transistors connected as a Darlington amplifier.  If one transistor has a beta of 25 and the other has a beta of 60, calculate the beta value of this combination.

Problems:

1. For the amplifier shown, if beta = 150

(a)  Calculate the input impedance at the base

(b)  Calculate the input impedance of the stage.

2. Shown here is a frequency response curve for an amplifier.  ESTIMATE the following:

(a)  What is the high cutoff frequency ?

(b)  What is the low cutoff frequency?

(c)   What is the  bandwidth?

3. An amplifier has a gain of 500, what is the dB gain?
4. A three stage amplifier system has dB gains of 15dB, 32dB and 6db.  What is the overall gain of the system in dB?

Module 6 Lab: Class A BroadBand Amplifier

Wire the circuit shown:

R1 = 68KΩ,  R2 = 10KΩ, R3 = 10KΩ, R4 = 200Ω ( two 100Ω in series ) , R5 = 2.2KΩ,  C1 = 0.1uF, C2 = 0.1 uF  Q1 = 2N3904

• Set the sig. Gen to 50mv  RMS.  With frequency equal to 10KHz.

• Record   v_ofor the frequencies listed.

vo

f ( KHz)   10KHz      25 KHz      50 KHz    100 KHz     500 KHz       1MHz    2 MHz   3MHz

Calc  Av

• Plot   A_vversus  frequency on semi log paper.