Questions tagged [transistors]

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

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Transistor gets too hot, what am I doing wrong?

I am very, very new to circuit design. I have designed a PWM circuit to control the flow rate of a small diaphragm pump. Prior to making this PCB I have demoed this setup on a solderless breadboard ...
duckfoot99's user avatar
2 votes
5 answers
172 views

TAOE3, Exercise 2.13 -> Verify that a 8°C rise will cause grounded emitter BJT to saturate

I have a question about this circuit from the Art Of Electronics by Paul Horowitz & Winfield Hill, 3rd Edition, Figure 2.44 below. For reference, we just learned about the Ebers-Moll equations and ...
AJ_Smoothie's user avatar
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Transistor base with resistor [closed]

I'm confused why the resistor R2 is used in this circuit. The resistor is parallel to the base-emitter diode of the transistor and therefore the voltage drop across R2 can't exceed the forward voltage ...
olympus_mons's user avatar
1 vote
1 answer
108 views

Camera trigger driver circuit using Arduino to 2N7000 N-channel MOSFET - off behavior with 47 kΩ resistive load

I'm making a circuit to trigger several machine-vision cameras. Simply splitting the digital output pin of a microcontroller, e.g. an Arduino, works fine for a small number (<5) of the newer ...
Andrew Spence's user avatar
1 vote
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46 views

Small signal equivalent circuit of multistage amplifier

I've been trying to draw the small signal equivalent circuit of this circuit and derive the expression for voltage. Using the equivalent circuit I drew, I derived the voltage gain expression but I got ...
Jefferson's user avatar
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Minimalist 3-input XOR gate using CMOS

As an enthusiastic noob to CMOS and after browsing multiple examples of XOR gates using PMOS and NMOS but finding it hard to find any good examples of 3-input XOR gates, I found an example of a 4 FET ...
David H Parry's user avatar
1 vote
1 answer
68 views

Voltage translator

I had an idea of a project to build which translate these respective voltages -3 0 and +3 volts into whatever the two variable power supply are delivering. See in the figure below the architecture I ...
Nedou's user avatar
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Pulling external PCB pin low via NPN transistor. How does it work?

I am redesigning a PCB which hosts an ESP32 and a display connector. One of the pins in this display connector needs to be pulled low or high. On the other side (display) that pin is connected to an ...
Andrea Baccega's user avatar
2 votes
1 answer
105 views

Is this the leakage current of a MOSFET?

I'm trying to understand the leakage current characteristics of a 130nm PDK in Cadence. I set up a testbench by grounding the gate and source terminals of a nmos FET, and setting the drain voltage to ...
George Guo's user avatar
3 votes
1 answer
77 views

Having trouble understanding a basic MOS OpAmp diagram

Taken from: Analysis and Design of Analog Integrated Circuits, 4th Edition by Paul R. Gray , Paul J. Hurst, Stephen H. Lewis, Robert G. Meyer. Page unknown. Hi. I am studying about MOSFETs and I am ...
It's_A_Me's user avatar
8 votes
4 answers
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Can I stack optocouplers in series to make a higher specification part?

Yet again I'm working with the sub-set parts the PCB assembler house has pre-loaded, and not what is commercially available. Like using 3-6 resistors in place of 1, and more relevant to this question; ...
user5211's user avatar
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3 answers
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Can I control any transistor (NPN/PNP) using a GPIO pin of my MCU? Is my schematic correct?

Can I control any transistor (NPN/PNP) using a GPIO pin of my MCU? Is my above schematic correct? EDIT 15/02/24: A REVISED SCHEMATIC, AFTER THE ANSWERS Is the revised schematic below now correct? My ...
Bala's user avatar
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2 answers
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Can a 2N7000 transistor withstand 4.7-5 V gate voltage?

Here is the datasheet of the 2N7000 transistor. I need to use it in a circuit where an Arduino will provide the gate terminal with 4.7-5 V and the transistor needs to withstand 200 mA current. It ...
Wanderer's user avatar
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2 votes
3 answers
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Pre-biased NPN BJT slow turn-off

In a PCB design I decided to replace a 2 kΩ resistor plus a MMBT3904 with a dual NPN transistor with built-in resistor in a SOT-363-6 package to save space and number of components. The part is ...
Luna's user avatar
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How to simplify FM receiver circuit to its core functionalities optically?

I plan making a FM receiver between 88MHz-108MHz. The required transistor for the radio circuit has often high voltage drop and I could not receive any hearable intereferences. What I had tried so far ...
lastime's user avatar
1 vote
3 answers
124 views
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Transit vs Unity Gain Frequency of a MOSFET

As far as I understand, the unity gain frequency of a transistor is its gain-bandwidth product, and the transit frequency of a transistor is a measure of how fast it is. I've also read that the ...
user_9's user avatar
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Why does the resistor need to be placed before the junction in an RTL NOT Circuit

I am trying to implement a simple inverter using transistors. I am confused why placing the resistor between the junction and the LED will not work, but placing the resistor before the junction does ...
michael_fortunato's user avatar
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2 answers
54 views

Help troubleshooting Mosfets in Switching Circuit

I've been trying to design a simple circuit to switch between two Supply rails (3.3V_SW & Vbat) while giving one of them a higher priority (3.3V_SW). The circuit in simulation is showing to be not ...
Sultanpepper's user avatar
-2 votes
4 answers
391 views

Recreate an inline 12 Volt Electronic Flasher unit for LED turn signals

I am trying to recreate the circuit for a TWO PIN 12 Volt Electronic Flasher unit for LED turn signals. It is the inline flasher "relay" that I need. Where power comes in the B (Battery) pin ...
Mouthpear's user avatar
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4 votes
3 answers
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Confused about finding max current through a load for BJT

I am trying to find the maximum current allowed through the load for a BJT transistor but I am having trouble understanding what I need from the datasheet. I know my base current is 1 mA but I do not ...
user avatar
2 votes
1 answer
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What's the source of electrons formation of inversion layer?

Until very recently I believed free electrons from the P-type substrate/body(minority charge carriers) form the inversion layer. This explanation works fine for planar MOSFET and FinFET type ...
Anirudh AS's user avatar
3 votes
2 answers
272 views

How can I make a non-inverting open-collector (or open drain) with a single transistor?

I had a PCB made for a homebrew SBC but while waiting for the boards I discovered a bug. I have a 74HC138 output (I believe this is just normal push-pull) that I need to hook up to a CPU pin but I ...
Procrastin8's user avatar
1 vote
2 answers
58 views

Switching between audio sources with transistors. Mimicking a SPDT switch

I have what I hope to be a really simple question I have to ask now as it stopping me sleeping lol. I’ve added Bluetooth to a 1950s car radio, using 2 SPDT switches (one could be replaced with SPST ...
Tom's user avatar
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6 answers
287 views

Effect of Vbe on Ic for a BJT

I am trying to find out where I have gone wrong in my understanding of BJTs: According to the Ebers-Moll equation: $$ I_C = I_S\cdot (e^{ \frac{V_{BE}}{V_T}}-1)$$ So if VBE decreases, then IC should ...
Xavier's user avatar
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HC-SR501 PIR sensor with 3.6V LED strip

I need your help with my HC-SR501. I'm not really deep into all the electronical device stuff, only got some basic knowlegde. I did some research here but didn't find a solution to my problem. I have ...
Patrick's user avatar
4 votes
3 answers
1k views

Timer circuits - difficulty analyzing

I'm looking for timer circuits without 555 IC and trying to understand them. There are some examples that seem easy to understand, but cannot wrap my head around the others. simulate this circuit &...
steve d.'s user avatar
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3 answers
145 views

Get 24 V from MCU instead of 5 V

I want to get 24 V from the MCU instead of 5 V so I decided to use a TIP141 transistor with current rated up to 10 A. My circuit is the MCU 5 V output power the transistor base basing through 10 kΩ ...
abdalla zakaria's user avatar
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1 answer
86 views

In a transistor, why can't current flow through the main circuit even if the control circuit is off?

This is a npn transistor The green part of the circuit is the control circuit. If I remove it and keep only the white part, the main circuit, the electrons should still be able to push through the ...
Saif's user avatar
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5 votes
6 answers
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Uncertainty of transistor hfe/beta values

When we buy transistors of the same type, what is the typical uncertainty of hfe and beta of the transistor? For example, if I bought two BC212B transistors in the shop, when I measure hfe, I would ...
wawa's user avatar
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Troubleshooting simple transistor circuit

I tried making a simple circuit as shown above. The battery BT1 is a 12V DC power adapter. D1 is actually about 6 LEDs in series. For R1, I tried 47 Ohm, 470 Ohm, 1K Ohm, etc., but D1 never turns on. ...
rosewater's user avatar
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2 votes
2 answers
83 views

Identifying an exploded diode, TO-220FP, -1020-

I have a children's electronic ATV that I'm trying to repair. It shuts off whenever power is sent to the wheels (even if the motors are disconnected) and the troubleshooting led me to examine the ...
Dawson Hampton's user avatar
0 votes
2 answers
155 views

Substitute 2N3055 with 2SC5200 in the John Linsley Hood 1969 amplifier circuit

Can I substitute a 2SC5200 for the 2N3055, without any other modifications to the following amplifier circuit? Input voltage is 24 V and biased to run at 1.2 A. schematic source : https://sound-au....
Ahsan's user avatar
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3 answers
50 views

RC delay timer to power LCD

I'm looking turn on the power of an LCD screen from a Pi Pico with a short time delay (50-100ms) after the Pico is plugged in. I want to power the screen with VCC from the Pico (5V) and use a signal ...
printsmith3d's user avatar
0 votes
3 answers
101 views

Charge Capacitor at 5V from 3.3V Microcontroller Pin

I must come up with a circuit that is able to charge a capacitor to 5V that I can drive through a GPIO of a microcontroller running at 3.3V. The capacitor is in a different device and has a leg ...
SukkoPera's user avatar
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0 votes
1 answer
39 views

Reading a negative voltage with ESP32

I am trying to detect when a switch is closed. The device connected to the switch is out of my control, but I have access to the wires feeding it. One side is ground and the other is -1.5v. (the -1....
bkanuka's user avatar
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0 answers
93 views

Transistor latch circuit stays on and button is unresponsive

I'm using a 2n2222a and 2n3906 with a 2n3906 as a reset and a irf4905 mosfet to carry the load I've redone this circuit many times on the computer, and breadboard and it seems to work but as soon as I ...
Kali Bot's user avatar
1 vote
3 answers
62 views

Selecting PNP transistor replacement

In my circuit I have a discontinued transistor listed here: If I can not select a transistor rated 350 mA, would a change to the collector current pose any issues that may need compensating in my ...
Wes Ellgass's user avatar
1 vote
1 answer
50 views

Understanding netlist IF statements

I`m reviewing this paper on how to do SPICE modelling for an FG transistor: https://digital-library.theiet.org/content/journals/10.1049/el.2011.0458 Inside there is a figure provided: I`m completely ...
starboy's user avatar
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0 votes
3 answers
146 views

Scaling DAC voltage to smaller range for controlling gate of transistor

I need to scale a DAC voltage which is ranging from 0-5V to a voltage ranging from 3.8-4.2V to control the gate of a mosfet in its linear region. I want the 0-5V range from the DAC to linearly ...
Nego24's user avatar
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0 votes
5 answers
151 views

Modifying this single-transistor circuit

In the circuit below, V1+D1 controls when Q1 conducts: when supplying a negative voltage, Q1 conducts. When the output of V1 is changed to 0V, Q1 does not conduct. How should I change it, so that ...
primare's user avatar
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1 vote
0 answers
62 views

Using NPN transistors for I2C level shifting

Background: I'm familiar with the method of level shifting an I2C signal using NMOS FETs and pull-up resistors. The Philips application note AN97055 documents the method and explains how it works here:...
nehfan's user avatar
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2 votes
3 answers
219 views

Why do I see unwanted current through this BJT switching circuit?

I built the following circuit but am getting a result I wasn't expecting. Here is a link to the CircuitLab model (I don't know how to upload a saved circuit to StackExchange): ...
RickyBoy's user avatar
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0 votes
1 answer
43 views

Control chip with a GPIO pin using a transistor and a push button switch

I need some help regarding a small circuit that I'm currently working on. I have a microcontroller (ESP32) that I want to use to control a chip with a GPIO pin of my ESP32 as output, and at the same ...
Reicken Back's user avatar
0 votes
1 answer
131 views

Identifying a transistor marked KS1212T for repair

I need help identifying a transistor marked KS1212T to repair a power supply. I have shorted the transistor. Please help me find a replacement part for it.
Игорь Никоноров's user avatar
0 votes
1 answer
149 views

I2C level shifter isolation

I am designing an FPGA-based SOM. There are I2C slave and master devices on the board. The I2C bus on the board includes an MCU that acts as a system manager and a bridge from UART to I2C, a PMIC ...
electroeso's user avatar
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0 answers
116 views

TB6600 / using with low voltage stepper motor

I'm using a classic TB6600 Stepper Motor driver (see for example link) I have a stepper motor that is rated for 5 VDC (datasheet). I have the datasheet, but it does not specify a current limit. I ...
user3533030's user avatar
1 vote
1 answer
96 views

Anyone have a Falstad simulation of a two transistor common-emitter amplifier? [closed]

I am trying to understand more fully how transistor amplifiers work and I've found the Falstad simulations to be very informative, especially the ability to place a mouse at any point and look at the ...
rhody's user avatar
  • 308
5 votes
1 answer
349 views

Transistor replacement for Novak Electronics [closed]

I am looking for a replacement transistor for a discontinued electronic speed controller by Novak Electronics - Ceased operation in 2016. The following is the information written on the transistor ...
Raman Dooman's user avatar
3 votes
3 answers
137 views

Base resistor on BC817-40

There are base resistor calculators and multiple questions are answered on the subject of base resistor calculation. However, the BC817-40 I am using from MCC is showing two different gains (HFE1 and ...
Gailu's user avatar
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0 votes
2 answers
101 views

Struggle with gated sound - Fuzz stompbox

I built my first fuzz pedal based on the Tone Reaper but I can't handle with gated sound. Whatever the fuzz pot is set the sound is gated. At low position the signal is very weak and chopped, even ...
Gwen Grand's user avatar

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