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Questions tagged [transistors]

The transistor is a semiconductor device that can amplify signals and switch power. Most used types are bipolar (BJT, for Bipolar Junction Transistor), UJT (Unijunction transistor) and MOSFET (FET, for Field Effect Transistor)

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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 ...
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3answers
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This is not my circuit, but anyway, What are they?

Hello. This is not my circuit, but I found it on Google. I'm just a newbie student, so I have two questions. Please, help me. (I started studying electronic circuit last week) 1) The meaning of ...
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Will these two transistors (BC558A and BC558B) function in the same way?

I'm currently following this guide on making an Arduino OpenTherm Controller. After finding almost all of the parts without any issue; my only question remained with the "PNP transistor" named in the ...
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1answer
33 views

Common Collector Amplifier and its name

Why is Common Collector amplifier is also known as Emitter Follower?
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28 views

Clarifications on Intrinsic Gain

I found this here while searching for questions regarding intrinsic gain but I'm still quite confused and the links given were dead. My questions are: Is intrinsic gain the maximum gain of a ...
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1answer
38 views

NMOS/PMOS Saturation

If I recall correctly, saturation occurs if \$V_{GS}>V_{TH}\$ and \$V_{DS}>V_{Dsat}\$ for NMOS. But is there an upper limit for the voltage? Like, when does a transistor not saturate after ...
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3answers
96 views

Inexplicable base bias

I have a common emitter amplifier on my breadboard (the same circuit as the image) with the following values: C = .01uF, R1 = R2=15k, RL = 5k, RE = 1k, and Vcc= 10v. The reason I have R1= R2 is I ...
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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 ...
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71 views

NPN transistor numerical

I think the steps will be STEP-1: \$V_x - V_{BE} = I_B\times R_E\$ STEP-2: \$I_B = I_{ra} - I_{rb}\$ STEP-3: \$V_x = V_{in}\times R_B/(R_B+R_A)\$ Please tell me i am correct or not??
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1answer
111 views

What does a transistor do? [closed]

Let's say I have a regular motor circuit using an arduino. The motor is a standard motor with a motor controller and I connect it to my arduino and get the code working but I realize that the motor is ...
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6answers
236 views

Simple LED fade circuit

I've been looking for a simple LED fade in/fade out circuit when power is turned on/off for a 12 V LED. I have tried the following circuits but the problem is that I can't reach the full brightness of ...
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1answer
55 views

Stepper Motor Voltage

I am having a problem making a stepper motor run. The problem is that the voltages that I am reading from the motor never reach zero (they move from a high voltage to a smaller voltage) so they never ...
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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 ...
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1answer
29 views

ESP-01 boots with GPIOs HIGH

I'm trying to implement a "button pusher" with some transistors controlled by an ESP-01 module, to push buttons on a remote control. I'm having an issue where if when the GPIOs (I'm using 0, 2, and 3) ...
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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 ...
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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 ...
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2answers
70 views

Gain of a feedback amplifier with base to collector resistor [closed]

I'm able to solve this problem using the concept of Miller resisitance however I'm having an issue solving this problem using the concept of feedback amplifiers. Can someone help me solve this problem ...
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2answers
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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 ...
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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?
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1answer
98 views

How MCU provides an output to pins [duplicate]

I would like to know how does MCU provide it's output current. here is a little drawing of my assumption (simplified) of how a pin is functioning when it is set to output. Basically it is a ...
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1answer
54 views

Phase shift in ce configuration

Please explain,How a 180 phase shift occurs in "ce" Amplifier. Change in input voltage leads to change in output voltage is some how I know, but this happen in "cb" Configuration too. When Vbe ...
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0answers
35 views

Transistor that keeps on-state or off-state without continuous electrical signal to the base? [duplicate]

Are there any transistor that keeps on-state or off state without continuous electrical signal to the base when used as a switch? I mean like light (mechanical)switch it turn light on or off without ...
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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 ...
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1answer
37 views

BJT circuit current analysis

Why is the current into the base Ib=Vbb-Vbe/10k? And not just Ib = Vbb/10k?
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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 ...
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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?
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1answer
29 views

Some questions about a transistor latch?

Below is a latch made up of two transistors: When the base current of Q2 is increaased this increases also the base current of Q1 which in turn increases the base current of Q2 more. So by such ...
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1answer
35 views

NMOS/PMOS Characterization

I have some questions regarding NMOS/PMOS characterization. I'm designing a common source amplifier using gm/Id method and since it requires characterization, I did so but using minimum lengths and ...
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1answer
53 views

Charge Pump Circuit explaination

I am trying to understand a charge pump circuit here but one part has me scratching my head and this sort of scenario happens a lot with me in electronics. It’s a question of what happened first?? If ...
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1answer
84 views

Connecting an IR receiver to Transistor for current control

I thought I had a simple circuit ready but I need help finishing it off. I’m using an IR receiver, transistor and a matrix of four 3MM LEDs. Want the LEDs to turn ON only when IR is detected. Using ...
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1answer
66 views

NPN Transistor- max power

I have studied the datasheet of an NPN transistor, in datasheet MAX-POWER OF transistor is mention as 400 mW. What is the meaning of max power? Can it be generated by itself or do I have to give 400 ...
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2answers
102 views

Shorting capacitors using a transistor?

Introduction First off, I'd like to let you know I am a beginner at electronics so some of the stuff I say might be very wrong. What I want to make is a 'spark generator' for lighting some gases in ...
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1answer
59 views

Transistors, explanation of current gain

At this first picture i have a NPN transistor with Beta=75, 2N222A transistor, both Inputs are 5V. it was very simple to calculate the current that will flow through the LED. as it is simply I1 * Beta ...
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3answers
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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 ...
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5answers
177 views

Emitter Resistor

Why is there a voltage drop of 2v across the C/E in the following circuit (XMM2)? I thought that a transistor behaves like a variable resistor, in that when you apply 0.7v across the base, it's like ...
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0answers
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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) (...
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1answer
27 views

Circuit to a/b switch like a relay would. So an analog or digital signal can be turned on or off or routed

I need to build an arduino-based switcher / router for a multi-arcade to route controls to different game boards, and also switch 2 vga inputs into one output. Without introducing any lag also. 3 ...
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2answers
132 views

Suitable transistors for adaptive motorcycle light project

simulate this circuit – Schematic created using CircuitLab I am working on something very similar to this, Adaptive LED Headlights – Model 8790 Adaptive 2 as a hobby project. I have controller ...
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2answers
69 views

Transistor Base/Collector voltage

I've read that with an NPN transistor, there is a voltage drop of about 0.6v between the base and the emitter. So you need to have about 0.7v on the base to switch it on (circuit 1) But what happens ...
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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 ...
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1answer
39 views

using TTL to drive LED

I have a TTL signal of 1 V, and I need to drive an LED by amplifying the TTL to 3 V. I used the following voltage amplifier circuit with Rc = 10 KOhm and Re = 1 kOhm. The DC input I use is 3 V. ...
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0answers
43 views

LEDs driven by GameBoy sound

My circuit does not work as I thought it should and I'm really confused now. What I want? Two LEDs which will pulse to audio LEFT and RIGHT channel separately. And same for display BACKLIGHT, but ...
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1answer
72 views

Current biasing in npn transistors [closed]

I need to calculate bias current Ic1 and Ic2. I understand that both currents are the same and, because of beta being infinity, there is no base current (Ic1 = Ic2 = Ie1 = Ie2) and Ic3 = 2 * Ic1. I am ...
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2answers
64 views

Weird circuit behavior at breadboard

I have no picture to show what my circuit is like, but I'll try to draw it and explain here as best as possible. The circuit contains a NE555 timer, working in the astable mode with a frequency of ...
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1answer
47 views

Making a DC motor turn in saturation and cutoff modes of an NPN transistor

simulate this circuit – Schematic created using CircuitLab So I have a DC motor that should turn with light on LDR and should stop when I cover LDR or turn off the lights. Basically the ...
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4answers
75 views

Non-inverting output of transistor circuit (at NPN base) is 0.69V max. why?

I tried to make a simple NPN transistor inverter so that I can use the strobe line of the parallel port to store data in two separate flip-flop IC's. (74HC174 and 74HC574) The IC that data will be ...
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0answers
55 views

NPN / PNP Sound activated LEDs

I have some RGB LEDs (common anode) and I'd like to control them via sound from my stereo (line level). I'd like to be able to switch the two behaviors of the LEDs from flickering off when the input ...
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0answers
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Do Germanium BJTs have lower impedance than Silicon BJTs?

What brings this up is the fact that Germanium has a higher electron mobility than Silicon(as well as lower barrier potential) and does that translate to greater admittance(including susceptance)?
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118 views

Can someone explain how I turned on a circuit by touching it?

I was just trying to learn how a transistor actually works by tinkering around myself. I have an Arduino running a flashing light program. I hooked up an NPN transistor to test out how I can make it ...
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Why doesn't current in an npn transistor flow with Vbe?

In the image, if i apply a voltage to the Emitter and push those electrons past the E-B depletion region through the base holes, wouldn't they accelerate in the electric field of the 2nd depletion ...