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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Which is better as a switch? [duplicate]

The offset voltage of a saturated transistor, makes bjt less attractive as a switch than mosfet. Why? Is there any other logics aside this?
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75 views

High-Gain Common Emitter Circuit

I am trying to design a high-gain common emitter circuit. I know that I need to use a bypass capacitor with emitter resistor to increase the gain. My problem is the formula A = Rc / re makes things ...
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98 views

Simple, Cheap, and Poor Quality Audio Amp [on hold]

So I am attempting to build/design a audio amp. Basically around a 1 watt amp for a walkie-talkie. I'm planning to run it off a 9V battery. When thinking about a power amp several ideas came to mind. ...
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1answer
79 views

BJT base resistor

I read this post: Which resistor for NPN transistor base? But I still cannot understand the base resistor calculation. I need the transistor to be a switch to 5V 200mA relay. The base will get its ...
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2answers
115 views

Transistor to run relay

In addition to my last post I have more information and details. I want to run 240V Relay (5V Coil) from my AVR chip (ATmega328P). My EMR relay takes up to 200mA on it peak. I have 2N2222 ...
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2answers
56 views

Reduce effect of supply voltage on pulse stretcher

Considering the following simple pulse stretcher, how can I reduce the influence of supply voltage on the pulse length? simulate this circuit – Schematic created using CircuitLab I ...
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78 views

Transistor rating with capacitive load

Considering the following circuit, how do I reliably protect the transistor Q1 from exceeding the collector current rating: simulate this circuit – Schematic created using CircuitLab ...
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1answer
55 views

What does multiple emitters/collectors imply in a BJT schematics symbol?

I sometimes come across with BJT symbols from which multiple lines come out of emitter or collector. Are such BJTs different kind of devices? What does it mean in solid-state level?
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1answer
46 views

Improve recovery time of discrete bjt monostable multivibrator

How can you improve the recovery time of a monostable multivibrator build of discrete pnp BJT transistors? I can't use integrated circuits like 555 timer since I need to tolerate voltages up to 36V.
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37 views

VCE in pnp transistor

If VCE is negative in a PNP transistor does that mean that it is in saturation? Note: not given the saturation value. This is related to a homework question. Thanks
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0answers
42 views

Voice amplification using BJT Amplifier and gaming headset

is there a way to hook up a gaming headset (e.g xbox) to a BJT amplifier so you can speak into the mic and hear your voice amplified in the headphones? I'm googling for an answer ...
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3answers
124 views

BJT Class A Amplifier - Help calculating resistor values \$R_C\$ and \$R_E\$

I'm having difficulty working out required values of resistors \$R_C\$ and \$R_E\$ in the circuit below. Can't seem to find any formulas on the web. I know how to find \$R_1\$ and \$R_2\$: $$R_1 = ...
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1answer
51 views

Real-life discrete monoflop

I my current project I need a high-side PMOS to disconnect a load once a over-current or (downstream) over-voltage condition is detected. Obviously without a permanent latch, once the PMOS opens, a ...
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3answers
135 views

How to drive optocoupler with BJT properly [schematics]

Recently I asked a question about optocoupler: Shematics: optocoupler controls a transistor and doesn't work as expected I have one more question related to the topic. PWM input comes from the ...
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1answer
57 views

What is the transconductance value of a given bjt?

In a BJT transistor Vbe is 0.7V and reverse saturation current is 10-15 A. What is transconductance value ?
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1answer
30 views

NAND gate from BJTs: interfacing +/- 12v op-amp and 5v logic: destroy BJT with excessive Vebo?

I want to switch on a relay when both a 5v logic input is high and a (LM741 used as a) comparator is around +10v, and the circuit I planned to use is below. The problem I see with the circuit is when ...
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1answer
37 views

Universal Voltage Divider Bias Circuit with both BJT and JFET

I am dealing with the following circuit: I am trying to understand if I can just assume that, much like in the JFET voltage divider circuit, V_G = 10/(40+10) * 16V , or if the presence of the BJT ...
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1answer
47 views

Help understanding 2N3904 VCE breakdown voltage?

While I was designing a constant current source using a 2N3904 I noticed a behavior on the bjt that prompted me to look closer into it. The issue is that although the datasheet specifies a minimum ...
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2answers
93 views

BJT vs MOSFET failure modes

I know MOSFETs are much more efficient than BJTs in that they don't consume as much power when on whereas a BJT consumes base current the whole time it is on. I also know that MOSFETs tend to fail ...
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97 views

Why is this BJT transistor saturated?

The bias point (without the 623mv input) is calculated as \$I_b = \frac{5-0.6}{5.5 M\Omega} = 800nA\$ \$Ic = \beta I_b = 290*800nA = 233\mu A\$ These calculations checks out in the simulator. ...
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1answer
108 views

Are BJTs used in modern integrated circuits to the same extent as MOSFETs?

On modern integrated circuits, are there as much BJT's on the chip as MOSFET transistor? If not, why?
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1answer
97 views

Why is BJT scaling not as significant as MOSFET scaling?

When reading about integrated circuits, MOSFET scaling comes up very often, however BJT scaling is never discusses. What's the reason for this?
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440 views

Basic operation of a bipolar junction transistor

I've tried really hard to understand the basic operational principle of a transistor. I've referred to many books and been to forums but have never got a convincing answer. Here are the things I want ...
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102 views

What's the rationale behind this choice of resistor for a BJT common collector amplifer?

As part of a design lab, we're using a common collector amplifier, and the instructor's choice for the emitter resistor makes no sense to me. The power rail is at V+=15 volts, and the load is 8 ...
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2answers
141 views

Simplifying microprocessor controlled mosfet switch

I need to switch a load, controlled by a microcontroller. (Actually, bypassing a load with a short-circuit.) My question is how to implement the switch. The circuit will have available to it the ...
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4answers
190 views

How does this BJT transistor work without any connection to its base?

I came across this circuit today and I am now wondering how that transistor works without any connection to its base. See below some schematics and a few images of it. If it works, is it safe to ...
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2answers
501 views

Best transistor to use for audio amplifier

This term, we will be designing an audio amplifier. So far in our lecture, we are still at BJT and based from what I've heard, FETs will just be partly discussed unlike the thorough one on BJT. ...
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1answer
79 views

Calculate BJT Amplifier amplification

I want to calculate the amplification of the following amplifier. I used the re model. I do the calculation this way.. So, in my case: So according to my calculation the amplification factor ...
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2answers
47 views

Calculate BJT Temperature when the output connect to 16V [closed]

Hi, Would need a help on how to calculate the BJT's Temperature when the "L" Output was connect to 16VDC? Need to know the Temperature dissipation of the BJT on calculation. Thanks Lee
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145 views

Typical Transistor Mismatch for 2N3904/2N3906

Suppose you build a differential pair from mmbt3904(2N3904 surface mount equivalent) transistors with mmbt3906(2N3906 surface mount equivalent) for a current mirror. You also use transistors that are ...
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2answers
97 views

Required Emitter Resistance \$R_E\$ for the Maximum Emitter Current for a BJT

I need some help. This can be a dumb question as I am not an electrical engineer nor an electronics engineer, but need to solve a problem as given below. I tried to solve it but not sure if it is true ...
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3answers
53 views

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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2answers
207 views

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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1answer
60 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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1answer
237 views

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
179 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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345 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
171 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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3answers
132 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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2answers
126 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
82 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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1answer
378 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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1answer
75 views

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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1answer
292 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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1answer
109 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 ...
4
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4answers
311 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 ...
4
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3answers
275 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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66 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
93 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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63 views

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 ...