Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [bjt]

BJT stands for Bipolar Junction Transistor. It is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications.

0
votes
2answers
150 views

Is the circuit in this answer wrong?

In the Q/A link below, the circuit in the answer seems to be wrong to me. Answer to "How to gradually light up an LED?" Circuit: simulate this circuit – Schematic created using CircuitLab In ...
0
votes
2answers
56 views

Dual power supply with BJT. How to do tracking without opamp?

I'm making a 0-±12V 20mA supply for breadboard. Circuit simulates fine with ltspice. How to implement tracking (or tracking ratio) WITHOUT opamp? I found a schematic here https://groenholdt.net/...
0
votes
2answers
71 views

BJT AC Analysis using r_e model

This is a picture of a Common Emitter Voltage Divider bias and it is been modelled using a CCCS and a diode resistance using the r_e model. Now my doubt is that I get problem in finding the input ...
0
votes
1answer
25 views

NTE 4050 buffer and current sourcing capability, datasheet reading woes

I am trying to construct an output that is switched on by the inputs to a buffer. The buffer input, in the final design, will be sourced from an Arduino or Raspberry PI. I needed the buffer because ...
0
votes
0answers
30 views

how C2 leads to negative feedback and C1 leads to positive feedback

C1 and C2 represent stray capacitances. I was told that C2 leads to negative feedback and C1 leads to positive feedback (pg 371 of Learning the Art of Electronics) and therefore C2 is good while C1 ...
0
votes
1answer
42 views

BJT (Common-Collector Configuration)

As we know that for the transistor to operate in the active mode, it should have emitter-base junction as forward bias and collector base junction as reverse bias. So the common-collector ...
2
votes
1answer
71 views

Reasoning behind values of CE amplifier

I have the following circuit: I am asked to choose values for the different components such that at the end, the amplifier meets certain requirements. In the solutions, I am told that to minimise ...
1
vote
1answer
50 views

Very slow turn-on time BJT (BUV27)

I have been asked to select a replacement BJT for a resonant circuit which uses the now obsolete BUV27. I have selected some based on V(CE) and hFE but all selected types perform a lot worse (low ...
2
votes
1answer
65 views

Input resistance confusion

Here's a circuit of an amplifier in the CB configuration: The small-signal equivalent is (using hybrid-pi model) I want to calculate the input resistance \$R_{in}\$. If I'm not mistaken, the blue ...
0
votes
1answer
51 views

TTL gate characteristics

In case of BJT for example, the input characteristics can be described with \$I_B=f(V_{BE})\$ and output characteristics with \$I_C=f(V_{CE})\$. How can the input and output characteristics be ...
0
votes
1answer
53 views

PNP BJT small signal model

I have been solving BJT circuits on my textbook and stumbled upon a PNP BJT small signal model question. It asks to build the small signal model of a PNP transistor circuit. When I checked the ...
0
votes
1answer
75 views

How can I build BJT amplifier with Vin and Vout requirements (peak to peak values)

I have been working on a project but I'm not sure if I'm complying with the requirements that I was given. Design a BJT amplifier such that VIN=0.1 V and VOUT=5 V (peak to peak values). ...
-1
votes
0answers
58 views

Determine the voltage transfer characteristics of the bjt

How do I start this question, I've just been trying to plot vin vs vout and using EBJ<0.5 and CBJ>0.7 and trying to get a range for vin and plotting? Is this the correct way to go about this?
0
votes
1answer
43 views

Why the input resistance of a common emitter amplifier is like this?

I am trying to find the input resistance of this BJ common-emitter amplifier: I replace the transistor with the hybrid-pi model It appears clear to me that the input impedance will be \$ R_{in} =...
1
vote
1answer
48 views

Base current and Vce relation in NPN transistor output characteristics

Regarding the active region of an NPN transistor and output curves, for a fixed Ib when the Vce is increased the Ic increases; namely Early effect. The reason if Im not mistaken is that the increase ...
-1
votes
0answers
20 views

cannot find high cut-off frequency from multisim

for the above circuit i cannot find the high cut off frequency by doing an AC sweep first picture is the frequency response. There is no dip seen for the fH.
2
votes
1answer
65 views

Current spikes on rising and falling edge of NPN BJT switch

I am simulating a simple NPN BJT switch for PWM in LTspice, and I observe some current transients on the rising and falling edges that I do not understand. The circuit is here: Picture of the falling ...
0
votes
0answers
21 views

Polysilicon Emitter equivalent for PNP BJT

I recently read (in the book semiconductor device fundamentals by Pierre about polysilicon emitter technique used in a n-p-n Bipolar Junction Transistor (BJT) to enchance the current gain of BJT. I ...
0
votes
3answers
54 views

Stability of BJT circuit using Re resistor

This is a post I found on Quora. I don't understand why decreasing Vbe decreases the current. Vbe=Vb-Ve To decrease Vbe you could increase Ve, Vb doesn't necessarily have to change, so neither Ib....
0
votes
0answers
44 views

Difference between current gain and overall current gain of BJT common emitter

What is the difference between current gain and overall current gain? Im guessing there is BJT current gain given by Ic/Ib Circuit current gain given by Io/Ii What is overall current gain and why is ...
0
votes
0answers
28 views

Current gain of common emitter bjt

On the right side hes used the current divider rule to calculate the output current Io through the Rl resistor. Looking at how the currents are defined on the diagram, shouldnt there be a negative ...
-1
votes
0answers
28 views

Measuring the resistance across Vce BJT

From my current understanding, BJT can be modelled as 2 back to back diodes. From a common emitter characteristics graph, Vce/Ic gives the resistance across the 2 diodes. It is high due the the ...
0
votes
3answers
107 views

What is the importance of the input and output impedance of a BJT

What is the significance of the input and output impedance in a BJT circuit? High output impedance means little to no current will flow at the output, why is this important?
0
votes
2answers
49 views

Output resistance of BJT common emitter circuit

I have found this circuit on a video, he talks about output resistance of the BJT of common emitter amplifier circuit not being infinite but very large so that it must be included in the re model. In ...
0
votes
2answers
55 views

BJT analysis resistance at the base using voltage divider

im currently confused as to why the resistance at the base is R1 || R2, ive done some research and looked at a couple of responses from people. But i still dont quite understand, could someone help me ...
-1
votes
0answers
26 views

Switch between charging source for LiPo battery using PMOS?

I have a 3.7V LiPo battery, a usb charger this one and a solar MTTP LiPo charger (this one). The goal is to use the solar charger as default and the usb as a back up. Especially, when charging with ...
0
votes
1answer
32 views

How does Dc biasing affect the Q point BJT

In order to amplify an AC signal, its required to provide a DC offset in order for no negative values of current to go through the input. Input signals and output signals oscillate centred on the Q ...
1
vote
0answers
32 views

Choosing a suitable FET for a design project

I'm currently working on a project to produce a high speed and high voltage pulse. I'm trying to find a suitable FET. I intended to supply a voltage of about 50v to circuit. And using the FET to go ...
1
vote
2answers
101 views

Common emitter amplifier gain with load resistor?

I have a problem I am working on where I have to find the voltage gain of the following circuit with a dc collector current of 0.3mA. My attempt at a solution involved using the formula A=-(RcIc)/Vt ...
0
votes
1answer
69 views

The BJT characteristic curve

Lets say you want to operate at 20uA base current. To move along that 20uA graph, you need to vary Vce. But to vary Vce, you either vary Vb (voltage at base) or change the values of the resistors at ...
-1
votes
1answer
49 views

What does the DC load in BJT mean?

I see a dc load line, what is the purpose of this line? There are 2 points i see, Ic(sat) and Vcc Does it have something to do with the maximum current through the device and the maximum voltage ...
3
votes
1answer
74 views

Calculating grounded emitter amplifer distortion (Art of Electronics 3rd Ed.)

Referring to section 2.3.4 A1 (pages 94-95) of the Art of Electronics 3rd Ed., I'm having difficulty understanding how to calculate distortion of a grounded emitter amplifier. The book says: ...
1
vote
2answers
39 views

How do the areas of the emitter, base and collector affect their respective currents?

I want to know what will be the effect on current if we change(increase or decrease) the area of the emitter, base, and collector. For example, if we double the emitter area what will be the effect on ...
1
vote
1answer
61 views

In practical BJTs, why can't Vce become 0 when the transistor is saturated?

Practically it is about 0.2 V when saturation starts. Why can't it go to 0?
0
votes
1answer
57 views

Bipolar transistor as a switch. Cut off mode?

I have a question regarding bipolar transistor and it's operation as a switch. I know that, in order to make transistor work as a switch, we need to avoid active region, meaning, we need to make ...
-1
votes
1answer
37 views

BJT circuit current analysis

Why is the current into the base Ib=Vbb-Vbe/10k? And not just Ib = Vbb/10k?
0
votes
0answers
45 views

Confirm re model of transformer coupled BJT amplifier

Could someone confirm my conversion of this transformer coupled BJT amplifier into a \$r_e\$ model? simulate this circuit – Schematic created using CircuitLab I get \$I_E\$ = 3.11mA and \$r_e\$...
-2
votes
1answer
97 views

BJT: Why do we need Rc and Re?

The below graph shows a graph for a BJT with Ic against Vce. Depending on Vce, there is saturation region, active region and breakdown region. These are resposible for different operations. In the ...
0
votes
1answer
49 views

Analysis of BJT transistor circuit

in the image, 2 loops are formed, is it possible to form a loop for the last one? If so, what equation would arise?
-1
votes
1answer
40 views

What happens to the low cut off frequency when replaced with a larger bypass capacitor?

When the emitter capacitance is increased to 100 microfarads. What would happen to the low frequency cut off of this amplifier?
1
vote
1answer
54 views

Trouble analyzing BJT circuits when we change β from very high to 100

For example we have this circuit: Originally we assumed β to be very high and we assume VBE = 0.7. So for this, we have IB = 0 and therefore V1 = -0.7V and V2 = 3.4V. Now that we have β at 100, IV1 ...
1
vote
1answer
36 views

BJTs to drive N-Fet

I stopped using BJTs for a while and now I cant figure out why this configuration does not give me a 12V PWM at the gate of the mosfet? I am only getting slightly more than my PWM voltage about 4.2V ...
5
votes
1answer
1k views

Logic behind this fuse status indicator

I was doing this circuit which I found on the Internet. My question is what is the logic behind the functioning of this circuit? Thanks!
0
votes
1answer
46 views

Confusion with a simple two stage amplifier design example

I have been following a lecture on net about a two stage amplifier example. It is basically a BJT amplifier with a PNP emitter follower as shown below. I named some of the nodes for clarity: The ...
0
votes
3answers
40 views

For MMBT2222; How to get hfe value to calcluate minimum base current to drive transistor in Saturation?

If my collector current VCC = 3.3V & Ic = 31.82uA then how to calculate minimum base current is required put transistor in saturation mode? Depending on it I will calculate base series resistor ...
-1
votes
0answers
40 views

Transistor as switch (in Saturation mode) - Why transistor saturation appears early with increase in collector resistor

This image is a simulation of a 2N2222 transistor as a switch to level shift 12V I/O signal to MCU compatible 3.3V I/O input. Simulation is done on LTSPICE XVII with DC sweep analysis of V2 (12V) (...
1
vote
1answer
56 views

MMBT2222 Datasheet doesn't mention maximum base current. How to calculate it?

The MMBT2222 Datasheet doesn't mention the maximum base current. How to calculate it? So that design should not exceed it. I want to use it for switching in common emitter configuration; where the ...
0
votes
2answers
32 views

Bjt for trigger MOSFET

I my project MOSFET need 13 v 65% PWM to trigger but controller output is 5 volt then how can I amplify this in voltage
1
vote
1answer
35 views

Analysis of voltage regulator circuit

I have found out the output voltage to be 9V. To find power, we need \$I_CV_{CE}\$ We can find \$I_E\$ from the output circuit. \$ I_E=\frac{6}{24k}+\frac{9}{10} \$ But can we find \$I_C\$? Or do ...
0
votes
1answer
52 views

How to determine operating mode of BJT transistor?

In the lab, I worked with this circuit: I varied RL over a range of values and measured VC and VE. Then I got the IC values and plotted the results down below: I am very confused as to how to know ...