# 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)

3,951 questions
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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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### 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 ...
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### How can I use a transistor (2n2222) to act as a switch with this 12V momentary switch? [closed]

I have a garage door setup that is basically like the following: All I want to do is add a new remote switch into the system. I basically want to add a circuit into the previous schematic in the ...
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### Not gate that differentiates between 0V and GND

A not gate typically just inverts the signal, so that V would turn into GND, and GND into V. Is there a not gate using transistors that would switch GND into V, but not switch 0V into V? (preferably ...
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### How to calculate the voltage gain in this picture?

simulate this circuit – Schematic created using CircuitLab I know that by using $A_v=-G_mR_{out}$, and $G_m=\frac{I_{out}}{V_{in}}$, we can get the voltage gain of this circuit. After the ...
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### Turn on/off ESP8266 by a transistor

I would like to turn off and on a circuit by another circuit. I believe that could be easily achieved by a transistor but when there is a voltage regulator and an ESP8266 with wide range of input ...
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### Cosimulation Error on Advanced Design System

I want to use BLF2425M9LS140, Power LDMOS transistor, to do cosimulation on ADS. I have got transistor's PCB design from its site and have done required procedure but when I try to convert layout to ...
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### Increase NPN transistor rise and fall time

I'm trying to emulate an automotive sensor with AVR and transistors. I have three resistors connected in series. Using AVR digital outputs (5V) to drive the transistors base, I "short circuit" to ...
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### Driving a 24V solenoid with a comparator under certain condition

I'm getting from a Hall Effect magnetic sensor a variable voltage between 0.8 and 3V. When the voltage is less than 0.9V, I want to activate a solenoid valve. If the voltage goes more than 1V, the ...
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### Mosfet Based impulse voltage generator

enter image description here **Details- Mosfet_1 will turn on for 20ms and charge the capacitor C2 and after that, it will turn off. Then the Mosfet_2 will turn on for 3ms with 40kHz frequency and ...
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### Can I use an NPN BJT transisor as a standard switch?

Is is possible to use a NPN transistor as a normal switch? If I put 5 V on the transistor base the switch is closed and if there is 0 V on the base the switch is open. Does the transistor need to ...
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### Double BJT circuit with one BJT off and one in saturation

In the circuit below, due to the base voltage, the circuit becomes a common-emitter setup. However, assuming a reasonable value for the base current the BJT should be in saturation. However the value ...
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### Frequency-to-Voltage convertor diagram questions

I'm relatively new to electronics, but I'm interested in making the Frequency-to-Voltage convertor linked here as part of a larger project linked here. Here is a diagram of the circuit I want to make:...
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### What transistor should I use? And how do I determine that?

Im new to designing a circuits. I've got my basic design done. I'm now trying to get to specific parts but I don't know which ones to buy. mainly because I don't know how to determine what I need. I'm ...
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### Discriminate MOS from BJT easily

I have a transistor for which no datasheet is available the transistor is supposed to be NPN (which implies BJT). (BD247C-Transistor-NPN, 100V 25A, 120W in TO220) how can I find out easily if it's ...
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### Explanation of this drawing (transistors) [closed]

I am very new to ECE and when i googled circuits for the beginner and this was one of them. So far i have a basic knowledge of transistors and that they exist. please correct me if i am wrong. ...
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### PNP Transistor switch circuit

I have been learning about transistors a lot lately. Following that I have managed to design a simple circuit that uses PNP transistor as a switch. Basically this is going to be a door alarm where if ...
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### Digitally selectable filter

I have asked a similar question but I did not get an answer, as it was too specific. So I will build on it but make it a bit more broad spectrum. I would like to make a digitally selectable BPF using ...
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### NPN BJT Transistor Circuit Analysis Problem: Is This Question Solvable?

I've been doing some circuit analysis questions as practice but came across one that seemed very odd: As far as I can tell, this question is missing information and therefore unsolvable? I was able ...
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### How to test transistor with Built-In Biasing Resistors

On a GPS device pcb, I found a small smd component that is marked as "22p V2". I found (tell me if I am wrong here) that it is a transistor like DDTA144WCA-7-F SOT-23-3 package, with built in biasing ...
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### Why does this simple circuit oscillate? (Ekasi oscillator)

Why does an Ekasi oscillator oscillate? From my research, I learned that when this is first plugged in, the capacitor is charging, so the LED doesn't shine. When the capacitor reaches 12v, then the ...
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I'm just a beginner, trying to understand an antennas and transistors as an amplifier, I'm studying, please correct me. Here we have a voltage source, PNP bipolar transistor emitter-base-collector ...
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### Are there cases where a transistor acts bilateral?

Some places mention an ideal transistor is unilateral. But is that the case in reality? For example for a BJT we say that the base current or Vbe controls the output port such as emitter current or ...
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### Why should Vbb not exceed the barrier potential values?

This has been mentioned in the book The voltage VBE across the forward-biased junction is very low (for a germanium transistor, VBE = 0.3 V; and for silicon transistor, VBE = 0.7 V). This requires ...
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### How to find the output impedance of a two BJT small signal circuit?

Like for instance, the picture above. How to find the output impedance? My thought was like draw the small signal circuit of them, then do the equivalent. But I am not sure if I need to short the ...
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### Forward biasing of a BC547 transistor doesn't turn on LED

I have a setup as shown below: simulate this circuit – Schematic created using CircuitLab I am using the transistor as a sort of a switch. I am ensuring about 0.7 V (approx) is provided from ...
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### Grounding in transistor circuits

In all example circuits using a transistor to power something (say, a motor), it seems to always be an NPN transistor (or NFET) with the something/motor connected to V+ and the collector/drain. This ...
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### NPN transistor as switch (actual voltage readings)

I started learning Transistors with this tutorial from the Sparkfun website. The tutorial is good and pretty easy to understand. So I decided to put my learning to the test and assembled a simple NPN ...
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### Digitally selectable filter for the ST7580 [duplicate]

For the ST7580, it uses PSK or FSK to send a signal over power lines. In the design guide the example is designed for an FSK or PSK signal to be transmitted at 80 kHz see page 23 for reference to the ...
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### Multiplexing LEDs

I’m doing a 16X32 LED matrix system. Controls via a PIC micro controller. The whole circuit is operating from a 5V source. For easy understand I have drawn a single Row/column how my hardware is ...
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### Question on current sensor sampling

I'm using this current sensor TLI4970-D050T4 located at the emitter leg of a power IGBT. This transistor is being switched at 10 kHz. How do I choose the convenient sampling frequency for the sensor? ...
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### using a TIP120 Darlington transistor to control a 12v fan from an ESP32 board?

I plan on making a version of this circuit to control a 12v PC fan using an ESP32. The ESP32 GPIO pins are 3.3v logic level. https://imgur.com/a/iqOfcME You can ignore the lower part of the circuit ...
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### Why doesn't current flow in the other loop?

I am just now learning about how transistors work, so please let me know if I have a misunderstanding. I ran a simulation of the circuit drawn below, and the results were that current flowed only in ...
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### Is it the quantum tunneling that causes the charges to go from emitter to collector rather than to base in BJT?

I was trying to figure out the working of a transistor and I find few things in the transistor action analogous to quantum tunneling like the width of base (barrier in case of tunneling) need to be ...
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### How to build a simple transistor switch?

How to build the following: A simple Transistor turn-OFF switch. A simple transistors circuit that has its own power source, but when I apply a second alternate power source then it will switch to ...
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### Howcome there is current flowing through the gate of this transistor?

I have a few conceptual questions: If there wasn't Rg (Resistor between gate and drain), would Vin = Vout then? For small signal analysis, current can flow through the gate (AC) if there's a voltage ...
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### Charasteristic curves for a transistor working in a common emitter configuration

Configuration According to my text book, When we use a transistor as an amplifier, there generally 2 resistors, one is input resister(R in) and the other is output resister(R out). Normally ...
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### Transistor Q's: Switching a Positive V when Base goes negative (and the other way 'round)

I thought I knew enough to get this working, but apparently I don't... I have a waveform going between +5 and -5V at audio rates. When the waveform is above 0V, I want to charge a capacitor from -...
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### Diode connected transistor for voltage biasing

I am trying hard to demonstrate that the transistor M1 in figure works always in linear region. Transistor M2 is diode connected and consenquently (I am using the EKV model) it works always in ...
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### AC analysis of Amplifier

I am quite new to ac small signal analysis of transistor amplifiers. I do not understand why a different model (like re) is required in the analysis while the DC analysis seems to work without them.
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### Add a relay to an existing switch

I want to add a relay or transistor, what fits the need best, to a simple switch, so I can control the switch by a micro computer but also keep the already installed switch so I can still operate the ...
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### Calculating the resistance for the base of a transistor

I'm building a circuit for my little niece's birthday (I'm already overdue with a couple of days). I started building it before I well understood enough about transistors and no I'm running a little ...
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### Improving a SRAM-based memory cell by reducing number of transistors

I'm working on Emulated version of a memory cell. It is a volatile single-bit memory. It uses 4 NAND gates to store one bit. I want to connect several of those memory cells together to create one ...
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### H-Bridge with emitter followers

I am currently reverse engineering a circuit which requires controlling of a magnetic field. For that, the circuit has a pair of D882 and B772 each. The PCB traces suggest that the transistors are ...
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### 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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### What does this part of a circuit with two NPN transistors do?

My grandmother asked me if I could fix her old portable record player, so I took a look at it and the motor wouldn't spin, so I opened it up and found a schematic inside. Nothing seems bad or broken ...
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### How does a MOSFET conduct in saturation region?

It is a simple question but I could not find a straightforward answer. When a MOSFET enters saturation region, the channel length starts to decrease, and the channel width is the smallest near the ...