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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100 views

Why does the current not flow directly to ground?

I'm working on an assignment for a digital circuit in a basic logic design class so I'm sorry if the answer is obvious! The title question is incredibly vague, but I wasn't sure how else I could title ...
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78 views

What are the possible disadvantages of using this PNP transistor?

I read this application note from Fairchild Semiconductors, and was wondering about what the possible disadvantages could be if a PNP transistor is used to bypass the Miller current as shown in the ...
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Understanding voltage drop on a transistor

I've been reading different answers online and am trying to get my head around calculating transistors. I have a circuit like this: (Imagine the base goes to a microcontroller and is connected ...
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6answers
395 views

Current mirror: real-life examples?

I'm looking for examples of how current mirror is used in real life. Most tutorials cover the circuit itself but don't go into examples. Therefore, I'm still struggling to understand how it's used and ...
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1answer
45 views

Saturation mode BJT explaining

If I have an NPN transistor and let's say we set the base voltage higher than the collector voltage.(Emitter is connected to GND).There are 2 currents flowing in the base because we have two forward ...
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1answer
30 views

hFE value (a.k.a β or gain factor) for transistor, at different voltage

I've been looking into the BC337 NPN transistor, and I saw in the hFE graph on page 3 of the datasheet, that the graph was at 1V from the collector to emitter. Is there any way to find out the hFE ...
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3answers
79 views

Ways to reduce Vgs range of Logic Level MOSFET

I try to control two MOSFETs from one microcontroller pin, where one MOSFET shall turn on 400 ms after the first one. The second MOSFET is switching on a relay coil. My idea was just to use a RC ...
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3answers
112 views

Understanding the biasing of a transistor with negative feedback

I am trying to understand the following circuit. However, I don't understand this step in the accompanying explanation: "A transistor with a large gain will cause a large voltage drop over the ...
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1answer
40 views

How to calculate the collector and emitter resistors in a differential amplifier with transistors

I'm refreshing my electronics knowledge a bit (after 30+ years), and I'm trying to build an audio amplifier from scratch without integrated circuits (transistors, and mosfets only). I'm trying to ...
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2answers
53 views

Voltage stability factor of voltage regulation circuits

Here a shunt voltage regulator circuit with two Zener diodes. One Zener diode Z gives the reference voltage at the comparator given by T1 for the feedback signal out Ra-Rb potentiometer. I can't ...
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27 views

Is it possible to make an on-off loop circuit with common transistors?

Can I make a circuit that turns something like LED or similar small DC devices turn on for a second then turn off one second then on and loop like this with transistor only? I mean without using any ...
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2answers
78 views

Choose and protect NPN transistor with resistor and diode

I'm working on my first circuit, controlling closet fans with an ESP32. I did some research drew the following circuit. I control the flow to GND from a 5V USB power supply with the GPIO pin thorugh ...
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1answer
64 views

How to activate DC motor when a certain temperature is reached? [closed]

I am a beginner in learning electronic circuits. I was trying to create a circuit on tinkercad that can activate a DC motor when a certain value is reached.
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1answer
42 views

SMD SOT-23-3 device identification - top marking E8LJ0

I have a small SOT-23 (3 pins, transistor-like) device that burned out (shorted between 2 pins). I need to identify it so I can replace it, but I can't find the code at all. The code is: E8LJ0 Thank ...
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57 views

How temperature difference does not affect transistors in CPUs?

Recently I learned about semi-conductors and some devices. Today I watched a video on youtube about a guy overclocking a cpu to 7.0 ghz, while cooling it with liquid nitrogen to -192 celsius degrees. ...
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1answer
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Use a transistor or MOSFET as a switch to control a solenoid [closed]

I am working on a project to control a solenoid (12 V/DC 12.96 W) with an ESP32. I have attached a circuit design as it is in picture. I have couple of questions: Would this circuit work properly? Do ...
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3answers
47 views

What's the difference between the maximum and cut-off frequencies of a single transistor compared to those of a circuit? [closed]

Many publications, when they speak about a single transistor, the maximum and cut-off frequencies are way higher than of the final circuit. Example: A modern FinFET, some report a maximum oscillation ...
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3answers
529 views

Decoupling Capacitor Loop Length vs Loop Area

When considering inductance reduction, what is considered more important? Reducing the loop length or the loop area? Below are two examples for visualisation, I am ignoring a lot of ways to reduce ...
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0answers
38 views

How to switch voltage using transistor

I have a 5V voltage source with 2.5A current as input. I want to have this source in the output. I use a microcontroller. I can't use a relay because it takes up a lot of space. I first used this ...
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0answers
28 views

Types of BJT DC Biasing Circuit

May I know this is a fixed-biasing circuit or voltage-divider biasing circuit? Component List R1 = 10K 1/4W resistor R2 = light-dependent resistor (approx 2K resistance under light) R3 = 2M2 1/4W ...
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1answer
53 views

AM modulator's negative peak saturation issue

I am working on AM modulator. I am using NMOS as a voltage controlled resistance, and opamp in inverting aplifier configuration to get carrier signal multiplied by input signal. I created a simulation ...
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1answer
76 views

Circuit design - How to fix power supply overheating and reduced performance?

Goal I'm trying to make a IOT radiator valve so I can manage the heating of every room in my house automatically with a system I'm building. Context I've pulled apart a cheap "smart" ...
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1answer
29 views

Transistor maximum base breakdown voltage

In a npn transistor with 5 volts VCE and current limited to 10ma by a resistor, it needs to drive its base with a DC voltage ranging from 3 to 500 volts DC, using a base resistor of 10 K ohms the ...
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1answer
60 views

How to safely use a transistor to control fans

I'm working on a project where I control two 12V 80mm fans with an ESP32. I've taken inspiration from various blog posts about fan control on the Raspberry Pi with a transistor (e.g. https://fizzy.cc/...
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2answers
41 views

Water well water level sensor (indicator)

I have a 400ft well, and I want to have a buzzer comes on every time water drops below certain level(280ft). At the moment, I got it working using a 12V battery and a multi-meter. I dropped down an ...
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2answers
45 views

How would I power a circuit and charge its battery simultaneously?

I have a circuit powered by a rechargeable battery. When a USB cable is plugged in, I want the battery to charge through a separate charging circuit and for the main circuit to be powered through the ...
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1answer
57 views

Switching between three output voltage settings on a switching regulator

I am currently in the process of designing a load control circuit based on a switching voltage regulator. The assumption is that the regulator would provide three different voltage settings based on ...
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0answers
50 views

NAND Gate Problem

As a practice question for our exam, we were given this circuit. The question was to find out which transistors have current flowing between the collector and the emitter and which do not. The problem ...
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0answers
58 views

Pinball keeps blowing transistor

I've a pinball machine that keeps blowing the transistor for the flipper coil. The flipper coil has a diode across the lugs. This tested good but I replaced it with a new one anyway. Still blows ...
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0answers
20 views

Switch to activate backup circuit

I am designing a device that will use a small heating element. The client initially designed it to use an incandescent bulb as a heat source. I want to maintain that as a back-up which will not only ...
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0answers
37 views

Load resistance of this circuit

I want to make sure I understood this correctly . If I want to measure the load resistance of this circuit, is it between (A - G) ?
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1answer
249 views

How dense is SRAM compared to random logic?

Modern CPUs always have some on-chip cache, typically more than one level. This takes a lot of die area; static RAM is generally reckoned at six transistors per bit. That having been said, the ...
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43 views

Why is this small signal model incorrect?

Here is the model I was told to redraw by replacing the transistors with their mid frequency small signal model: And here is my attempt at doing so: Upon receiving feedback, I was informed that the ...
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2answers
159 views

How to activate one LED separately in a group of LEDs?

I want to activate one LED in a group of LEDs depending resistance varies linearly depending on the temperature. I am using variable resistance that Controls how LEDs will light. LED1 and LED 2 and ...
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1answer
43 views

Qualitative explaination of Output Characteristic of Transistor (BJT) using Depletion layer between Collector and Base

From my understanding, The diffusion layer at a p-n junction is an equilibrium of two opposing forces on charge carriers due to 2 forces - Concentration Gradient and Electric Field caused by Bias and ...
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2answers
57 views

What is the effect of an amplifier on an LC tank?

Consider a simple circuit like this: The tank on the right is an oscillator and the amplifier provides in-phase "boost" to the tank to keep the oscillations going. its controlled by the ...
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2answers
63 views

Transistor: Getting “incorrect” graph for input voltage to output voltage

I tried drawing the graph of \$v_o\$ vs \$v_i\$ for a bipolar junction transistor. I used the below setup (common emitter:) By design of how the base is a small part compared to others, \$I_b <<...
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0answers
23 views

Identifying source and drain for a transistor [duplicate]

My question is related to this post (the comments below). Basically, how can I identity the source and drain of a transistor ? I thought that drain and source were totally symmetric inside of NMOS or ...
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2answers
72 views

What is emitter repeater?

According to what I read the circuit above is the schema of emitter repeater, it is used between two amplifiers to connect them and it's gain A = 1; it does not amplify the signal. But I want to ...
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3answers
84 views

Driving a 5v logic input from a 3.3v output

I have a device which requires a 5v logic input. That input ordinarily needs to be high and the device is activated when the input goes low. I need to drive this from a 3.3v output (RasPi GPIO) which ...
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0answers
39 views

Having trouble finding a good transistor to turn off boost converter with Arduino

I have a 3.3V volt logic level Arduino that is powered by a single lipo cell. Also connected to that lipo cell is a boost converter that boosts the voltage from 3.7V to 170V to drive Nixie tubes. ...
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2answers
72 views

Switchable current shunt resistor

Looking at the reference design given for INA826 in the image below, what would my best options be if i wanted to replace J8 with something allowing me to switch in R19 (sense resistor) from a ...
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0answers
51 views

Can I use this circuit to control model trains with?

I am currently researching and developing several arduino/attiny projects for model railway applications. One of the projects is a method to 'catch' an analog train and gently slow it down using a ...
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0answers
44 views

Making a transistor circuit with sharp turn on (Small threshold interval)?

I am measuring an analog voltage which should trigger an MCU by a GPIO when it falls below or goes above certain thresholds. At first I was planning on using comparators in order to get well defined ...
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0answers
45 views

How to open/close a high (~110V) voltage circuit from a low voltage (5V) one with a transistor?

I'd like to turn on/off a Nixie tube from a 5V circuit system (Arduino). I've found a solution that uses transistors (1 pnp and 1 npn). Can't we do it with 1 singe transistor? What to consider? What's ...
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4answers
2k views

My capacitor does not do what I expect it to do

Fixed: The capacitor was defective. It works well with a different one. I’m new to electronics and need your help. I built a circuit similar to this one (see comment for the exact components): I ...
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4answers
79 views

Current limiting circuit operation

I cannot understand how this current limiting circuit works. Image source: UNLV Physics Department, Bill O'Donnell, Current Limiter Circuit Here is where I get confused: When Q2 is turned on, the ...
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40 views

Two PNP Transistors - Jumper Collectors with Emitters and Bases at Same Potential?

In the attached image, OUT1 and OUT2 are logically identical (provided for redundancy). I'm wondering if it's valid for OUT1 and OUT2 to be tied together and brought across a single load? This is ...
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1answer
70 views

Driving lamps with the fewest number of NPN switch transistors

I'm building a small system to drive some Nixie lamps and I'm missing some of the classic ICs that could make this design significant simpler. I ended up with some discrete NPNs to select the lamp and ...
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1answer
83 views

Need help to correct circuit

I am using this circuit to detect whether or not electricity is being consumed. There are two sensor sources (CT1 & CT2 ) where a CT coil will be installed. When electricity passes through that ...

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