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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20 views

Biasing a emitter follower darlington configuration

Below picture is a simple voltage regulator(link to simulator): The current at the op amps output is at nA region(why?), how can I increase the current at the op amps output without adding a third ...
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2answers
505 views

Transistors - What is re model?

I would like to know an in depth definition of the re transistor model in BJTs. I know most diagrams very well, but the definition does not. Also, can you guys help me differentiate the small scale ...
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1answer
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How to drive segment display and sens button press at the same time? Understanding this schematic

I have a very simple board that has been designed by the Italians back in 2001. It has 3 7segment common anode displays, 2 buttons, and a few LEDs. I have to interface with it but I don't know how it ...
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Will a BJT blow up if there isn't any load/resistance either in collector or emitter?

Taking NPN BJT as example. When an NPN BJT is operating in the active mode, \$I_C = \beta I_B\$. That means we can fully control the current pass through the BJT by controlling \$I_B\$ only. In such ...
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1answer
45 views

Current at the collector

In the following circuit When I simulate with ltspice, why do I get 29.6 mA in Ic with Ib = 100uA ? I'd expect it to be 10 mA, according to the example in the Malvino book, chapter 6. When R1 = 1K, ...
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Cut Off mode of an NPN transistor with PSPICE

]2 I am trying to model the cutoff mode of an NPN transistor with a switch that is connected to the base. Unfortunately, it shows current going through. I am using ORCAD Capture. Does anyone know ...
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3answers
176 views

Transistor Voltage Switch - Circuit Help Please

I've been a lurking mechanical engineer for a while, metal fatigue specialty. I could really use some help with a simple circuit design please! I have two pseudo-constant voltage sources that can ...
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1answer
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Poor little TO-252 went in a blaze of glory - can you help ID?

This guy is from a dishwasher control panel. I'm having trouble finding a replacement for the entire control unit (that will ship to Japan, anyway) and I am handy with a soldering iron. Can you take ...
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4-20mA to switching output

I have a 4-20mA output. I need to turn an LED on when let's say 20mA is reached. I can obviously do this easily with a plc or an Arduino, but I need to do it as cheaply as possible. Is there a simpler ...
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Driving a stepper motor (0K57STH56-2804A) with transistors

I want to drive a stepper motor for a homemade CNC machine but I'm not so experienced so any help would be great. I'm working off of this site: https://www.digikey.com/eewiki/display/Motley/How+to+...
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3 Input AND Gate with RTL Logic

Quick question here - are there any downsides to building a 3 input AND gate like this? simulate this circuit – Schematic created using CircuitLab
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What is the best transistor model for bjt transistor ac analysis(middle response)?

Nowadays I am working on bjt transistor ac analysis. I use r(e) model for bjt transistors ac analysis in my university. I know there are separate methods for low frequency medium frequency high ...
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Identifying exact type of transistor

I can not identify the exact model of this transistor. It reacts as a bipolar NPN Si transistor with EBC pin configuration (first image left to right,) not ECB! This seems to be made by Siemens. ...
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Choosing a resistor for connecting a bipolar transistor

I need to run some LEDs using Arduino. The total current consumption is about 190 mA. For these purposes, I found a bipolar transistor PMBT2369 (Nexperia). Transistor characteristics: - Maximum ...
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Is transistor the only electronic component on a CPU?

I have been reading about CPUs recently and came to know that all logical blocks and memory on CPU can be made out of transistors. So is it the only electronic component on CPU? Edit (Made after ...
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Can anyone solve with this circuit the problem is with resistor in series with diode?

Can anyone solve this problem ?? I want vout analysis The output is in green ? Why the capacitor voltage is -10 from vout to node above vin ?? In first negative cycle the current will move anticlock ...
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Reversing the input of a transistor

I want to detect if a 12V DC line has power or not. I want the transistor to work like this: If pin 2 has 5-12V, pin 1 and 3 should be disconnected and should stop the flow of 5V 2A across pin 1 and 3....
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Adding a transistor to cut the power makes automagically any device more power friendly?

I'm currently designing a device that will be powered by batteries, I'm planning to make the MCU sleep and only wake up a few times a day to read sensor values and go to sleep again, one of the ...
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How does the heater circuitry work?

I have this BreadMaker that I want to modify. I do not have the schematics or the sources. Below is the schematic I draw of the circuitry of the heating element. The microcontroller is 5V and output ...
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3answers
54 views

How to amplify 3.3V to 10V by using an NPN transistor? How to select resistor based on current, how does the amplification happen?

I have basic knowledge about NPN transistors and I know how they work: for current gain based on the small input current in the base we are able to drive large amount of current in between collector ...
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1answer
48 views

BJT Base-Emitter Voltage

I have a question about Bandgap Reference circuits. How did he get Vt*ln(n)?? This is how I did it:
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56 views

How to find Base, Emitter, and Collector Voltage of a Circuit Demonstrating Miller Effect

Given \$R_S=100\ k\Omega\$, \$R_1=150\ k\Omega\$, \$R_2=20\ k\Omega\$, \$R_C=7.5\ k\Omega\$, \$R_E=1\ k\Omega\$, \$C_1=C_2=C_E=0.1\ \mu F\$ and \$C_{BE}=10\ pF\$ I need to solve for \$I_C\$, \$V_B\$, \...
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How can I choose a MOSFET based on Rds? I have understood all the parameters except this

I have understood all the parameters except Rds and conduction loss. Please explain them to me. I am using a lithium-ion battery pack of 36 V and its maximum voltage is 42 V to drive a motor. Motor ...
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58 views

Amplify square wave signal generator output to high voltage?

Let’s say I use a signal generator to create a square wave and then want to transform it into a high voltage of, say, 5 kV. How can that be done? Are there transistors that can handle that kind of ...
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120 views

ESP8266 not working to drive relay

I am trying to drive a 5V Relay using ESP8266-01 module. Following image is the circuit diagram i have uploaded. My sketch is about connecting the esp to the mentioned Access Point and controlling ...
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1answer
58 views

How to sink more current than specified?

I am using the TLC5940 (datasheet) in an upcoming project to control the cathode side of an LED matrix, but each of my LEDs needs ...
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5answers
227 views

Why does adding an emitter resistor to a common emitter amp reduce its gain?

According to the Wikipedia page for common emitter amplifiers, the addition of an emitter resistor decreased the gain of the circuit. However, to me it appears that if the resistor was omitted, then ...
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Darlington resistors in autopilot burn from backcurrent [closed]

I Have a fairly old (mid seventies) autopilot on my sailboat that has four darlington transistors (SM2174 and SM2184) in the output to the motor. They burn easily if the wheel is turned manually, ...
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1answer
41 views

Finding the necessary currents for AC analysis for CE NPN BJT amplifier

I have this circuit with a CE NPN-BJT amplifier and I am struggling to find the necessary values for calculating r(pi) for AC analysis, i.e. the hybrid-pi model: $$r_{pi} = \frac{V_{thermal}}{I_b}$$ ...
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1answer
151 views

Switching IC via FTDI232 DTR and transistor

I am trying to switch an IC on/off via the DTR signal pin on an FTDI232 USB/TTL Serial converter. Basically during the flashing of my ESP8266, I need to be able to power the IC off and then on again. ...
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67 views

Why PMOS act like “close switch” when zero voltage

in PMOS that Vtp less than 0 , from what I understand if We give Vg less than Vtp it has current flow from source to drain ,on the other hand if we give Vg more than Vtp it cut-off. but in digital ...
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4answers
831 views

Simplest amplifier?

I've built a very simple VCO based on a UJT transistor. Source: Sonelec-Musique.com. It outputs on a 8-ohm speaker but sound is like really, really low. So, I'm looking for an amplifier to build, ...
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1answer
45 views

I want a 4ohms 1w to 3w transistors type amplifier? [closed]

I need a simple 2n2222a amplifier circuit for 4ohm 1watt speakers and I am using these fore my pc Note : not for headphone. Only for speakers... And some one pls explain how to build a simple ...
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4answers
9k views

Why can current flow through the reverse biased base-collector junction (N-P junction) in a BJT with a forward biased base-emitter junction?

If the base-emitter junction of a BJT is forward biased, then current can flow through the reverse biased base-collector junction (N-P junction). This disagrees with my understanding of the PN ...
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28 views

Use multiple transistors in order to control multiple buttons on a remote

It is my first time using a transistor. I saw tutorials on the internet and thanks to those tutorials I manage it to work. But the tutorials only illustrate this using one button. I got one button ...
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1answer
69 views

Help with BJT Transistor analysis. The amplified waveform is more like a square wave any needs to be more sinusoidal

I have been exploring BJT transistors and implemented a common base amplifier. I connected a signal generator to the voltage source labelled V2 in the below schematic. The oscilloscope image shows ...
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1answer
157 views

transistor replacement dp35dp

Hello I have an old Intel Motherboard DP35DP, I was using this board as a file server using RAID (Its crucial to get that RAID array working again). It seems like the culprit is a transistor, its ...
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1answer
106 views

PNP transistor switching and inductive load

I am designing a circuit to control a motorcycle horn (its operating frequency is 490 Hz, its resistance is 3 Ohm, and it consumes 1A on average as indicated by the power supply), and LED lights. The ...
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6answers
79 views

Way to show that the current through a Darlington pair is determined by the emitter resistor

I have the following circuit: simulate this circuit – Schematic created using CircuitLab Is there a way to show that the current through \$\text{R}_1\$ is given by \$\text{V}_\text{i}/\text{R}...
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1answer
72 views

Current Mirror Circuit

Below is a sample current mirror circuit. I understand that If the transistor Q1 is connected in a diode connected BJT configuration and the Transistor Q1 and Q2 have identical transistor parameters, ...
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2answers
157 views

Transistor Question

I have pasted a picture of a circuit. The transistors with an open circle on them are n-type. This meaning that a 0 voltage( or 0 input) activates the transistor. What I don’t understand is how to see ...
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70 views

BC457 transistor shuts down entire power on high signal

simulate this circuit – Schematic created using CircuitLab I'm making a microcontroller circuit to control a heater using an ATmega328, a 5 V relay, a 16x2 LCD display, a transistor etc. Now ...
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1answer
28 views

Reverse Phase Dimmer MOSFETs

I have a comprehension question regarding the design of a reverse phase dimmer. I have a picture attached of the part of the circuit I do not understand: The line is connected to the Drain of Q2 and ...
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1answer
199 views

Choosing transistor for amplifier

I'm going to design amplifier, requirement is that impedance for in should be more than 20kohm, impedance for out should be less than 50ohm, and voltage gain should be more than 200. So I'll make cc-...
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1k views

Thickness of Depletion region, transistor

I came across a doubt regarding thickness of Depletion region in different regions of transistor while reading an online article. It says that the thickness of Depletion region in collector is more ...
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1answer
125 views

How to increase current while keeping the voltage the same?

I currently have an Arduino Uno board which has an output of around 5V @ 900mA. Is it possible to bump up the current to around 3-4A while keeping the voltage the same? Maybe with a transistor, but I ...
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83 views

What is the purpose of this resistor between BJT Base and Emitter?

Can someone please explain to me what the purpose of this resistor is?
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1answer
143 views

Controlling the power supply of a bluetooth module via GPIO and a transistor

I want to be able to turn a Bluetooth module on and off via a GPIO pin of a microcontroller. My first approach to realize this with a transistor is shown below. Is this approach correct? If not, how ...
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1answer
56 views

Which characteristic of a BJT determines the timing in the following given application?

I currently face a question about the BJT circuit given here: We see a 2N3904 transistor with constant base current of 2 mA. A switch seperates a 15 V/20 ohm source from the collector of said ...
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23 views

Replacement of BSV81 transistor

A 40 year old cruise control unit (sample and hold circuitry) has failed on me and I'm looking to replace a BSV81 transistor to see if it fixes my problem. This is an old n-channel depletion mosfet. A ...

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