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.
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BJT switch connections [duplicate]
If an NPN BJT is being used as a switch, why is the load usually connected between +Vcc and collector? How is the performance affected if the load is connected between emitter and ground?
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Gain in Common Emitter Amplifier
I need to design an amplifier having a Vin=150mVp, 1khz; Vcc=3V that can run an 8ohms, 0.25 watts speaker, with a gain for about 7 without noticeable distortion.
Below is my designed voltage divider ...
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41 views
NTE912 Pinout Confusion
The NTE912 contains three standalone BJT transistors and two configured as a differential pair. The datasheet can be found at
http://www.nteinc.com/specs/900to999/pdf/nte912.pdf
and gives a pin ...
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How to design a schematic diagram of amplifier that can drive 8 ohms 0.25 Watts speaker? [closed]
I have here a schematic diagram for amplifier that drives a 0.025watts 8ohms speaker. But what I need is an amplifier that drives a 0.25 watts 8 ohms speaker.
So, here are my concerns:
How can I ...
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1answer
110 views
BJT audio amplifier for 8 ohms 0.025 watts speaker
I have to analyze an amplifier circuit for 8 ohms, 0.025 watts speaker and don't understand how it works. What is the working principle of the components? What configurations are used? In which stage ...
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249 views
Why are BJTs more reliable than MOSFETs under severe weather conditions?
I read in a textbook (Microelectronic Circuits by Sedra and Smith, pg. 494, sixth edition) that BJTs are preferred by the automotive industry due to their reliability under severe weather conditions. ...
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2answers
105 views
Which resistor for NPN transistor base?
Which is the way to choose a resistor for a NPN transistor base?
I want to use P2N2222A as a switch, in a design as shown below. When I have voltage in base (1.8 V), I want a connection to be created ...
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120 views
Transistor biasing, Large Resisor values
simulate this circuit – Schematic created using CircuitLab
In above circuit the base of Q1 acts as a level-shifter from 3V-50V at it's base to 2.8V. The base of Q1 is driven by PNP ...
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97 views
Why is collector current independent on collector base voltage in active region
I read many books but none of them explains why the collector current is independent on collector base voltage in common base transistor in its active region.
Please explain it with clear mechanism.
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1answer
59 views
BJT collector-emitter saturation voltage vs temperature
I'm using a BJT as a switch, so it will either be off or saturated.
I'd like to know how the collector-emitter voltage (when saturated) varies with temperature in general, (but perhaps take the BC179 ...
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100 views
Applying hybrid-pi model of an npn-BJT to a pnp BJT in small signal analysis
When doing the small signal analysis of a circuit containing a pnp BJT connected to either the emitter or collector (or base?) of a npn BJT, is it possible to apply the hybrid-pi model for the npn-BJT ...
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Measuring input resistance to a MOSFET/BJT amplifier
How would one go about measuring the resistance of a Emitter follower in PSPICE?
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162 views
NPN is physically symmetrical yet the model isn't? [duplicate]
It just strikes me as very odd that all representations of the actual physics of NPN transistors in textbooks is perfectly symmetrical, yet neither the diagram used to represent them nor the ...
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78 views
Help with NPN and PNP common emitter
I have a circuit that has the emitter side of a NPN tied to the emitter side of PNP. I need to find the output voltage on the emitter. Base voltage is a sine wave. Can someone help me understand what ...
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4answers
250 views
Why is this BJT not going into saturation?
I built a project based off of this description, but substituted an STGP7NC60HD IGBT. See the schematic below (Note: IGBT symbol doesn't exist as of this post, so JFET was substituted). The coil and ...
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3answers
197 views
BJT vs MOSFET for very low power flyback converter
I am currently working on a flyback design charging a capacitor in the nF range to 200V from an input voltage of around 1.5V. As the final circuit should be as small as possible, my component choices ...
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53 views
Voltage gain of an emitter follower
For an emitter follower the voltage gain is given by \$A_v=\frac{r_o|| R_L}{(r_o|| R_L)+r_e}\$, where \$r_o\$ is the output resistance of the transistor and \$r_e\$ is the intrinsic resistance of the ...
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1answer
65 views
Lower corner frequency in an emitter follower (Common collector)
I have a doubt about the lower corner frequency of an emitter follower.
I don't rember where, but I have read that it is given by:
\$\omega_L=\frac{1}{R_BC_1}\$ where \$R_B\$ is given by the parallel ...
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Intrinsic resistances of a BJT amplifier: how find them?
I'm studying the low-frequency response of a BJT amplifier. I can't understand how I can find, for example, corner frequency \$\omega_{P1}=\frac{1}{C_{C1}[R_B || r_{\pi}+R_{sig}]}\$ where ...
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1answer
89 views
Very Simple Discrete Current Source
I'm trying to work out why someone would choose the right circuit over the left one. The only thing I can think of is, that one on the right can be made an adjustable current source by making \$R1\$ ...
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Why do we assume VGS<Vth and Vds>0 for a mosfet in cuttoff and Vce>0 for a BJT in cutoff?
The devices below are both n polarity devices, the BJT is a NPN and the MOSFET is a NMOS.
For the BJT in cut-off, why do we have to assume \$V_{ce}>0\$?
For the MOSFET in cut-off, why do we have ...
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193 views
Why emitter follower is so noisy and distorted in large signal?
I have a signal around 20 V peak-peak. I want to feed it into an emitter follower BJT and I have no experience in working with such large signals.
The BJT is well in bias point ( I tested the ...
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38 views
Confusion about the Injection of electrons and electron holes in a BJT
On page 354 of the 6th edition of Microelectronic Circuits by Sedra & Smith under Current flow, the following statement is made;
Current will consist of two components: electrons injected ...
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Can Emitter Follower BJTs work with large signal?
Sorry for such elementary question.
As anyone knows emitter follower design of BJT has some specifications . For example they are suitable for driving low impedance loads and so. But because the ...
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replacing diode connected BJTs by simple diodes in a current mirror circuit
Why cant we replace diode connected BJTs by simple diodes in a current mirror circuit?
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BJT variable Voltage Gain Distortion
This is a very basic question. I want to have a very simple BJT Signal Amplifier with variable voltage gain. Let's think about a common emitter with an emitter resistor like this:
The input signal ...
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2answers
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breakdown voltage in BJT
How breakdown voltage of common base configuration is higher than that of common emitter configuration??
in common base, break down is more or less similar to PN junction breakdown.
please explain ...
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BJT in saturation, a circuit analysis question. how to approach question like that?
there is a question I cant solve.
I know that \$\beta\ =50\$ and \$V_{ce}\ (sat)\$ \$ =0.2 \$
I need to find the value of \$ V1 \$ that the BJT is in saturation
I've tried some KVL/KCL equation ...
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Designing yet another BJT amplifier given some constraints
Sorry for asking a question about the same subject as my last question, but I am once again stuck on a BJT Amplifier design problem.
Where the beta parameter may vary from 100 to 800, the voltage ...
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1answer
152 views
NPN transistor circuit connection, what determines which region it is at?
I know that for an NPN transistor to be in the active region, the base emitter should be forward biased and the base collector should be reverse biased while for the NPN transistor to be in the ...
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323 views
Designing a BJT Amplifier given some constraints
I am trying to design a BJT amplifier following this model:
Where the beta parameter may vary from 100 to 800, the voltage between the base and the emitter equals 0.6V (active mode), \$V_t = 25 mV\$ ...
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Transistor part number selection software
I know there are online/offline softwares for finding equivalents or known transistor datasheets but is there any software that works inversely? For example that I can ask the software for a ...
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183 views
How to determine BJT switching time
Is there some standard way to get information about BJT (Bipolar Junction Transistor) rise and fall times (the high power ones) ? In essence a IGBT is a BJT being driven by a FET, so there should be ...
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Is a darlington constructed with 2 BJTs fully equivalent to an integrated one?
Is a darlington constructed with 2 BJTs fully equivalent to an integrated one? The reason I'm asking is that there are obvious differences, like the collectors which are separated, and also the ...
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153 views
How to control the gain of FET/BJT/Op-Amp amplifier by input voltage range?
Assume I have an input voltage ranging from 5-10 MHz and want to amplify it.
The case is pretty simple as any device as FET,BJT or high frequency op-amp can do the amplification well but I have a ...
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When are BJTs used in common base configuration?
BJTs are mostly used in common emitter, sometimes common collector configuration. I rarely see common base. When would you use a BJT in common base? For instance, what parameters are different from ...
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How do I check a BJT transistor if it is still functional?
Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective?
simulate this circuit – Schematic created using CircuitLab
Say ...
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Zener Noise Generator - NPN BJT Amplifier Analysis
I'm interested in creating a low voltage white noise generator by means of a zener diode, as detailed here: Zener & BJT Noise Generator. Specifically, I want to use the circuit here, in order to ...
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Emitter follower: Icq and Vceq calculation
I have problem with understanding how to calculate \$ I_{cq} \$ and \$ V_{ceq} \$ of this circuit.
Q1 has these details:
\$ h_{FC}=150 \$ and \$ h_{fc}=100 \$
As I understand it I should find \$ ...
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2answers
373 views
Why are the current directions in the hybrid-pi model for BJT the same for both NPN and PNP?
Here is the hybrid-Pi model:
with Ic and Ib going in, and Ie going out.
The same circuit can be used for both NPN and PNP, the only thing changing being Vbe for NPN and Veb for PNP.
The currents ...
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5answers
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BJT input connected to another BJT's output and loading effects
Sedra & Smith Microelectronics, example 6.10, page 390. They ask us to analyze a BJT circuit. Here it is:
simulate this circuit – Schematic created using CircuitLab
In the next ...
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Why can't two series-connected diodes act as a BJT?
Another form of the question is: will joining two diodes with wires (pn-np) make a transistor-equivalent?
I read that they are not equivalent, but why?
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4answers
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Different answers when using two different equations to find the same unknown (BJT)
Problem 43, chapter 6 in sedra and smith microelectronics.
simulate this circuit – Schematic created using CircuitLab
We are asked to find the current flowing in R1 and R2 knowing that ...
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154 views
I don't understand this question about BJT in Sedra and Smith
Chapter 6, problem 32.
simulate this circuit – Schematic created using CircuitLab
Design the circuit to establish a curent of 1 mA in the emitter and a voltage of -1 V at the collector. ...
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Finding the (Q) point for V(Collector-Emitter) and Collector Current?
The question gives the following schematic and says to find the Q point for the Voltage(Collector to Emitter) and the Q point for the Collector Current. It gives beta as 50.
I'm using two standard ...
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Common Emmiter BJT config
In From Schematic to Reality @ beavisaudio.com, the following is written:
...
R2 and R4 form a voltage
divider. This simple snippet is in charge of providing half of the 9
volt source ...
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559 views
Alternative to emitter-follower for simple BJT voltage regulator
I want to make a voltage regulator from one or two BJTs and a zener diode. However, I would like to be able to make full use of supply voltages when they are lower than the voltage that the regulator ...
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53 views
SK3024 BJT equivalent
What are the parameters/procedures in finding an equivalent for a SK3024 BJT?
Do I focus on similar maximum ratings for collector current and current gain?
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Making a controllable H-bridge
UPDATE
I found out the issue. Specifically, the PNP transistor I got. I used a BC557 - for some reason its collector-emitter current is very very low. It does open when the base-emitter junction goes ...
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628 views
Gain of common-emitter BJT amplifier with bypass capacitor
I have this common-emitter BJT amplifier:
simulate this circuit – Schematic created using CircuitLab
The text book says that with a bypass capacitor, the gain is -Rc/re, where Rc is ...
