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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Reading recommendations to better understand how to understand the intended function of a circuit

This is a general question. Suppose I have a circuit like below from CircuitDigest:  My supervisor said that about the circuit that.. [The] circuit does actually involve an amplifier, even ...
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Starting on electronics from zero - transistor timer

I'm just starting on electronics, trying to build a few circuits but can't understand properly how things work. I got this circuit and put on a breadboard, but the power source I have is 5V instead ...
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How to project a FET transistor as an amplifier?

I am trying to solve a problem on using an FET transistor as an amplifier with the common source configuration. The model should be appropriate for high frequencies. The problem gives the equivalent ...
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Transistor is not switching-Raindrop sensor with LED (Later Buzzer will be used)

I am creating a small application in which on detecting the water the Buzzer will ring. But right now I am testing with LED instead of Buzzer. Raindrop Sensor datasheet link: https://components101....
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Find DC components of npn and pnp transistor

I'm sorry but I can't seem to figure this transistor question. The question goes as follows: Draw a DC-circuit and determine the unknown component values. Which DC-voltages ( reference is ground) ...
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Role of input resistance in LM384 Audio Power Amplifier

let's consider the LM384 Audio Power Amplifier (here the datasheet) Can you explain me why is there the 150k resistance? It lowers the device input impedance, which is not good for a voltage ...
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How do we create current sources?

Constant current sources (simply, current sources) are useful and necessary devices. They are widely used to drive LEDs, charge capacitors and batteries, to bias differential amplifiers, etc. The only ...
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Amplifying photodiode current with BJT transistor

I'm trying to develop a kind of light detector. To do that, I'm going to use a photodiode and a bjt transistor to amplify its current. I found a circuit in this tutorial: which explains how the ...
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Using Thevenin Theorem to solve for unknown values in BJT voltage divider circuit

Assuming this is a DC bias of a voltage-divider type BJT circuit: V_CC = 10V Beta value = Not Known V_BE = 0.73V (Base-emitter voltage) And the Thevenin circuit ...
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Determine the transfer function using these values (Capacitors)

This is my circuit. simulate this circuit – Schematic created using CircuitLab These are the values of the components Determine the transfer function using these values This is what I ...
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Should I count transistor power while transistor is switching?

When transistor (bipolar transistor in common emitter amplifier) is closed (not conducting) or opened saturated (enough base current, collector current is limited by the resistance of the load), it ...
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Determining the component values for Dc

Draw the circuit diagram for DC and determine the component value. The transistor must be biased with : This is my attempt to solve this The picture bellow is the way I drew the DC circuit diagram ...
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What if I switch the place of the load in a common emitter NPN transistor circuit?

As you can see in the picture, there's an NPN transistor in a common emitter configuration. In the first configuration, the load is placed between the collector pin and Vcc, and it is the most ...
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Large Signal Transconductor

I have a basic question about the following circuit, which is introduced in the book " and is described as a "large signal transconductor": It says that: the capacitance value is chosen to be a ...
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Magnitude of a function with inductor and capacitor

I have a homework problem with the following circuit: I have solved the transistor biasing part and then drawn the AC-circuit of it. Then I need to find the transfer function. These are the ...
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How to connect a photovoltaic to a heating element directly

I am trying to connect a photovoltaic panel directly to a heating element (coil) without using a battery or an inverter and switch it on or off by using a transistor or a thyristor. I am well aware ...
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Power dissipation BJT transistor as voltage follower

Following the discussion from this thread I am finalizing my calculations. I am not sure that I am calculating the power dissipation correctly. Given the following circuit I need to operate the opamp ...
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527 views

MOSFET and BJT transistors

What is the main difference between a mosfet transistor and a BJT transistor. I know both are used for amplification and can be used as switches. But where would you use one over the other and what ...
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182 views

Simple Transistor Resistor Amplifier Circuit Question

Can Someone Please Help Me On Solving this. I have tried and stuck..In a point that can I apply Kirchhoff's Voltage Law around R2,R4 loop. simulate this circuit – Schematic created using ...
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Hows does this 12v relay works with transistor voltage drop?

I'm working my way through "Make: Electronics" by Charles Platt and came across the following schematic: As someone who just recently got started with electronics, what I can't wrap my head around is ...
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MOSFET-based ring oscillator not oscillating (but oscillate in simulator)

I created the following ring oscillator: In the LTspice simulator, it is supposed to oscillate at ~3Hz (LTspice source) given the 47nF caps and 680kΩ resistors: I then built this design on a PCB ...
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Finding the magnitude of the Transfer Function

This is the circuit, where some of the components values where given and the others, I found myself. (Sorry I have no link to the design, I needed membership there) The following part says to draw ...
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Why is this MOSFET KVL to find VDS not right?

There was an answer provided for this question I'm working on, but it seems that my answer was wrong. The sticky note has was the "correct answer" is supposed to be, but I don't understand why V-minus ...
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Why are there three transistor pairs in Class B Power Amplifier circuit?

I have a Class B amplifier circuit to be done in lab. Why three pair of transistors are used in this? I suppose one is a Darlington pair but what is the requirement of the third one. Also, why there ...
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CMOS Flip-Flop Design

I'm new in Transistor-Level Design and for that reason, I have practiced and learned from designs that I found on google. When I tried to design a mux from scratch without relying on the design of ...
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Is placing the ground in this small signal model wrong?

There is an example in a text where it shows the small signal model of a circuit. Below on the left there is a transistor circuit and on the right its small signal equivalent: I'm a bit confused ...
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Capacitor in series with transistor base

I am fairly new to electronics and just had a quick question. I saw the following suggestion for a one shot trigger to wake up an ESP from for example a PIR sensor with one shot trigger and to read ...
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How do we explain the common-mode feedback in an intuitive way?

There are such beautiful circuit ideas that make you hold your breath and admire them silently. Such an idea is the common-mode feedback (CMFB) in fully differential amplifiers. I was not familiar ...
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Analyzing a simple circuit with transistor

I've been trying to understand how to analyse circuits with transistors, but I'm having a hard time finding out where to start when confronted with the following two types of circuits. (Gain = ...
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Equations for voltage/current through a transistor

Given the following circuit: I can figure out the current through the 'bottom wire' by doing: ...
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161 views

When does a transistor turn on

I am having a very hard time understanding when exactly a transistor turns on. For example in the following circuit from Everycircuit: Why does the transistor turn on when the push button is off, but ...
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Switching buzzer on and off with two transistors

I want to make a simple water level indicator with tank full alarm as shown in the diagram. What I want to achieve is, when the tank is full to 100% and water is still flowing through the inlet pipe (...
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Small electronic project kit

I ordered this electronics project kit which consists of a small PCB. You have to solder the components onto the board. The components are: Two 510 ohm resistors (green, brown, brown) Two 33k ohm ...
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The detailed working steps of the DRAM 3T1C cell?

This question is related to this one. But the focus is a little different so I put it here. I tried to understand the detailed working steps of below circuit. It is an old 3T1C DRAM cell circuit. ...
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esp32 relay control

I'm designing this circuit for my esp32. I need to control 2 dpdt relay 424012. One is on the board, the other off board. This relay controls both 220 V and 12 V lines. I'm using 2n2222a for switching ...
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Deriving the small signal model of this transistor

Given that the current equation for a graphene transistor is given by equation (1) I'm trying to find the small signal model of the transistor. $$(1)\space \space i_D(V_{GS},V_{DS})=\frac{W}{L}μ(C_{...
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Ghosting on Nixie Tube Clock

I have problem with my nixie clock. There are ghosts when changing numbers on the lamps. I'm using multiplexing with TLP627 opto-coupler to control anodes and NPN MMBTA42 bipolar transistors to ...
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Draw the corresponding AC circuit

I have the following transistor, whose I have calculated the parameters that were not given. Now, I want to draw the corresponding AC circuit. Can someone help me with this or give me any source ...
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Transistor, operating point problem, best way to start a problem

I recently started studying electronics and I have been recently studying transistors, and I didn't quite get the spiel to these kinds of problems where you have to find its operating point. I don't ...
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What happens to the body effect and the channel length modulation for the short channel devices?

Does body effect and channel length modulation effective for both, short and long channel devices?
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Why is reading the 3T1C DRAM cell not destructive?

Could anyone help explain how the above 3T1C DRAM cell works? T means transistor and C means capacitor. Why is reading it not destructive?
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Why does this transistor circuit work?

In the following circuit, why does a certain amount of current flow into the transistor in the below circuit? I can understand once the push-button switch is turned on, there would be current flowing ...
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How I can solve this BJT?

I edited circuit like this: I tried representing currents like: $$ \begin{aligned} &I_{R1}=100_{B1}+I_{B2}\\ &I_{R2}=101 I_{B2}-I_{B1}\\ &I_{i}=101 I_{B2}+100 I_{B1} \end{aligned} $$ ...
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BJT high frequency analysis

I have a little bit of confusion on how the textbook author is determining the high frequency cutoffs for the parasitic capacitance parameters for a common emitter amplifier. This is Boylestad ...
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124 views

Is this resistor routed correctly?

For a friend I'm trying to make a fuzz pedal and found this very flexible fuzz circuit, called "The Fuzz of 1000 Faces," at instructables, credits to Randofo. However, since it's an old post, I ask ...
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Transistor as a heater device and measured by LM35 temperature sensor?

The aim is to make a temperature control circuit using an Arduino Uno as a controller, an LM35 sensor as feedback to measure the actual temperature, a TIP31C transistor as actuator to control the ...
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Visual example of PNP transistor

Following this question, Visual example of NPN transistor, is the following a correct understanding of a PNP transistor? To be honest, I have no idea why the top of the transistor (where the current ...
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135 views

Visual example of NPN transistor

Is the following a correct understanding of an NPN transistor? Basically, a positive voltage source needs to flow through the Base of an NPN transistor and out through the Emitter, so it needs to ...
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47 views

Requirements for NPN, PNP transistors

Is the following a correct understanding of what makes a NPN/PNP transistor turn on or off? NPN (more common) Must have voltage > ~0.7V on base Must have (conventional) current flowing into ...
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Understanding a PNP switching circuit

Description I have the following diagram in which a switch connected to a 5V source should control two PNP transistors. I've spent a few hours trying to further understand PNP transistors to better ...

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