Question

Could someone please help me on how I should be configuring the circuit in Figure 4(a) in Multisim? Basically not understanding question #1 in the Procedure. Cannot keep Vrb the same value while adjusting Vcc. Then when trying to adjust Vbb to hold Vrb, Ib changes.

Any help is appreciated!

Discrete Devices Section LAB 4 BJT CHARACTERISTICS AND BIASING Objective: The objective of this laboratory is to examine the operation of a bipolar junction transistor and plot its output characteristics and the DC load line for a given configuration Prelab: Review the data sheets for 2N3904 and 2N2222 BJTS and answer the following on a separate sheet of paper. Use the description and the notation for each parameter as given in the data sheets 1. Determine the maximum collector current for both 2N3904 and 2N2222 transistors. 2. Determine the minimum and maximum or hfE at Ic 10 mA for the 2N3904 transistor 3. Determine the maximum power rating Po for both transistors at TA 25°C. 4. Determine the collector-emitter saturation voltage at Ic 10 mA for 2N3904. 5. Determine the maximum input and output junction capacitances, and noise figure for the 2N3904 transistor. 6. Determine the dc operating point for the circuit of Figure 4(b). VR Vcc 15 V Rc 1 kn 100 k2 Rg 330 k VRC 1kn 2N3904 2N3904 Vвв Vcc RE 510 Figure 4(a): BJT test circuit. Figure 4(b): BJT bias circuit. V&e=\,5®V V« « - 1.033 1. Breadboard the circuit of Figure 4(a). Refer to 2N3904 data sheets for the pin Procedure diagram. With Vcc 0, set I to 10 HA by adjusting VB So that VR is 1 V as given in Data Table 4-1. Then set V to 0 V, 0.2 V, 0.5 V, 1 V, 2 V, and so on, by adjusting Vcc while measuring and recording Ic for each CE in Dala Table 4-1. 11

Answer 1

As you have mentioned that Vrb is varying ,

During the simulation , the Vrb is slightly deviated to around 0.89 V which is adjusted at the beginning to 1V

This is because the increase in Vcc causes the Vce to change and eventually produce an increase in current Ic with a small decrease in the base current Ib so as to maintain the emitter current Ie.

Since Ie=Ib+Ic.(The transistor maintains this current equation)

Therefore due to the small  decrease in the current Ib, the Voltage drop Vrb across resistor Rb will also vary.

Procedure:

a)connect the circuit as per the figure.

b)set Vcc to 0v, Then vary Vbb using potentiometer in multisim as in the screenshot attached and vary it to make Vrb=1v and Ib=10uA.

c) Now increase Vcc by varying the potentiometer to make Vce = 0.2V and tabulate the readings of current Ic and collector to emitter voltage Vce which is later used to plot output Characteristics of the transistor.

d)Repeat the same Step C by making Vce=0.5v, 1v, 2v so on and tabulate the readings of current Ic and collector to emitter voltage Vce.

The above readings can be used to plot the output characteristics of BJT.

The sample Screenshot of the multisim circuit is provided below

II Interactive MISC Place Indicator 2 XMM3 A XMM2 XMM1 XMM4 -.. - U2 DC 1e-0090hm ... .. -.. - 1.266m B R2 1k0 .. .. Q1 2N3904 R1 9.326u Multimeter-XMM4 . .. 100KQ R3 iVccc 10V R4 1000 20% Key A DC 1e 0090hm Vbb 101000 84% Rey-A 1.98 V dB A V Set... Design1