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Questions tagged [npn]

A type of bipolar transistor comprised of n-type semiconductor in contact with p-type semiconductor which in turn is in contact with a n-type semiconductor -> thus NPN. The transistor has three terminals, the Emitter, Base and the Collector. Current injected into the base controls the flow of ...

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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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52 views

Transistor Reverse Biasing - AC

I am working on a project which require to activate a 24V Rated relay using a 3.3V rated IO. To provide adequate isolation I have added a Opto-isolater stage. In order to increase the current output ...
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84 views

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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64 views

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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Test a transistor with a multimeter

I used the guide at https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07 to test a transistor with my DMM. The NPN transistor I used to test is the "mospec tip130 No11D" ...
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96 views

What is the function of this npn transistor?

I see that the R306 resistor is trying to limit current when the npn transistor is on. I am not sure what the resistance offered by the npn is but it looks like the current through the 47k resistor ...
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73 views

Operation of BJT with low values of Vbe (“cutoff” region)

Many sources claim that when the base-emitter voltage becomes smaller than approximately 0.6V-0.7V, the bipolar junction transistor goes in the cutoff region and there is zero base and collector ...
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40 views

Command Solid State Relay using NPN transistor 2N2222 [duplicate]

I'm trying to command a Solid State Relay with the HV1 pin, I can't connect it directly(HV1 to CH1) due to the fact that the impedance on that pin is too low and I only obtain 2.8V when connected. So,...
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Voltage controlled switch simulation

I'm trying to short two pins on a chip when an audio signal is received and float them otherwise (same effect as a tactile switch). I thought the best way would be to use a voltage peak holder and a ...
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2answers
118 views

Prevent NPN Transistor Base-Emitter Current

I'm making a simple AND gate array out of 2n2222 transistors. Here is one cell: simulate this circuit – Schematic created using CircuitLab When Input "A", is disabled, and "B" is still on: ...
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78 views

Driving a power-good LED with two open drain outputs

So I have two same DC/DC step down converters and I'd like to have a green LED driven with the converters' open drain PGOOD signals. The signal is active-high and the LED should be on, when the power ...
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92 views

High voltage linear regulator (with pre-regulator)

I need to build a linear voltage regulator like this: The problem with the usual linear regulators (LM317, LM337, ..) is the limited voltages they can withstand. I have taken inspiration from a ...
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59 views

Problem with the fall time of a NPN transistor

I have the below circuit to translate a slow digital MCU on/off (3.3V) signal to a higher voltage signal (range from 12 to 24V). I have a specific attention for the Vin=12Vdc case, the voltage drop ...
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2answers
64 views

Read a value of open circuit or GND

I'm trying to make a circuit that have in input a "not connected" or "GND", and the output is a function of input. For example if there is no connection, the outpur is 3.3V. If the input is connected ...
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64 views

How to protect LEDs from high voltage during NPN transitor transitions?

I am using a 555 timer and an NPN transistor to drive an array of 12 LEDs from a 9v battery, and a potentiometer to control the duty cycle. I am concerned about the voltages the LEDs will be subjected ...
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115 views

How to amplify RF signal to high enough level for a CMOS downconverting mixer?

I've been reading original academic papers on mixers and now a RF textbook and I have been unable to understand a very basic thing, which is how do I get a RF signal, say -65 dBm, at a high enough ...
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58 views

Non inverting OpAmp with NPN amplification factor > 1

I need to amplify the output range of a DAC chip from (0-3.3 V) to (0-10 V). Unfortunately, I cannot simply use an inverting OpAmp circuit, because the output needs to stay positive with respect to ...
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66 views

output resistance of discrete amplifier

I have the three-stage amplifier below. I am interested in finding the output resistance of it. Just wanna check if am doing it correctly? Thanks simulate this circuit – Schematic created using ...
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87 views

Transistors with different loads in parallel

My circuit roughly looks like this: I want to send a signal to uC and turn on a LED when there is light shining on phototransistor Q3. Currently I'm using stm32f4 (discovery board) as a signal ...
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3answers
61 views

Can I connect Inductive Proximity sensor to two different PLC

Some background, I have a tractor that I want to make semi-autonomous. The tractor has it own PLC and an NPN Proximity sensor to measure speed. I have industrial PLC by Unitronics (V130) with I/O ...
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1answer
113 views

Keep Blowing out 2STN1550 Transistor [closed]

I'm (Trying) to build a trigger timer for an air cannon to launch ham radio antennas. This is an attempt to only allow the valve to stay open by a consistent interval to get max distance without ...
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59 views

Enable a 5V relay from a 1.3V LED with a transistor

I am really just starting and I would like your help on a simple but important project. So there is a circuit that when something happens an LED lights. When I measure I see that it is 1.3V so I ...
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47 views

Finding Drain voltage of current mirror

Below I have a current mirror loaded differential amplifier. Can somebody please Just give me an idea of how to find the drain voltage, vd8. I am stuck because I don't see the relationships that can ...
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108 views

All NPN transistors work the same way?

I have a doubt and I cannot find a certain answer on the internet. All NPN transistors should work in the same way?, I mean, the only difference in all the models are just the rating currents and ...
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Switching HCSR04 with a PNP transistor and ESP8266

I want HCSR04 sensor to work for once in 10 minutes. So I thought I could use a transistor and reduce power consumption. But I could not use a NPN transistor because HCSR04 works even if the ground ...
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525 views

NPN transistor slow to turn off even when operated outside of saturation region

I am currently studying how transistors react and behave to simple signals. I have the following circuit: A square wave of approximately 83kHz is applied. The transistor used is a 2N5551. The ...
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121 views

Toggle two LED status lights with two transistors

I have an input that is either floating, or grounded. The switch is fixed, it's either open or closed. Ie, I can't replace with a double throw. Here is the schematic / sim. If the switch is closed, ...
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1answer
54 views

Enable one or two of the same output via switch (minimalist schematic)

I'm making a PCB and my real estate is limited. I am using an AT89C2051 microcontroller, and it only has one serial transmit output. What I need is a way to set whether the output from the serial ...
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3answers
170 views

What this NPN transistor circuit do?

I need some help to figure out what this NPN transistor circuit do, how it works and why it's needed in order to make the CSR64215 bluetooth chip work. Here's the schematic: And here's what MFB ...
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1answer
190 views

maximum possible common mode voltage for npn

First I would like to thank everybody here for providing the help. This great resource allows me to understand things beyond what my textbook only offers. I have the question below: Here is the ...
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1answer
65 views

Finding a range for a common mode signal

I have the question below Here is the figure they are talking about: (Text and images from: "Microelectronic Circuits" book by Sedra/Smith, 7th edition, chapter 9) Here are the answers to the ...
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2answers
82 views

finding the output resistance of npn current mirror

I have the following BJT based current mirror for part a, I used an approximate analysis illustrated below: \begin{equation} V_{B2}=0.7V=V_{C2}\\V_{BE1}=V_{B1}-V_{C2\:}\rightarrow V_{B1}=0.7+0.7=1.4=...
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Using LTSpice to find the gain of NPN-PMOS folded cascode

I am trying to use LTSpice to find the gain of NPN-PMOS folded cascode. Below is the question prompt: In the problem, the parameter specifications are as follows: \begin{equation} \beta =100,\:V_A=5V\...
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1answer
77 views

LM311P op-amp strange behavior in comparator mode

I'm trying to build a schematic which will turn on a relay in case motorbike battery voltage will reach some level. I've ended up with the following schematic. simulate this circuit – Schematic ...
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1answer
64 views

prox sensor with NPN open collector output or a dry contact

I am totally new in this field. I want to use a 5 V / TTL signal from a National Instrument to switch on/off a Red lion PXU series temperature controller. But this controller required a dry contact ...
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617 views

Npn transistor failed to work

Sometimes after long time working correctly and turning on and off inductive load, Darlington NPN transistor (ONSEMI BD679) which should follow signal (IN4), fails to work and turns on inductive load ...
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78 views

Switching positive and negative voltage with npn transistor (or multiple npn transistors)

I need to switch negative and positive voltage with npn transistors, but I am not sure if npn transistors work in both ways. How to do something like this with transistors?
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82 views

circuit analysis for an amplifier

so I had my original circuit looking like below: simulate this circuit – Schematic created using CircuitLab I was able to simplify it to look like as follows: simulate this circuit but now ...
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88 views

BJT theory and practice - please help me understand

I've never built a circuit using BJTs before but I'm more inclined to go this route over FETs for this task. I have 3x 12V 200mA (approx.) loads in a vehicle which I want to switch on with only a 12V ...
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294 views

NPN Transistor To Control LED Strip

I am new to the use of transistors and couldn't find exactly how to select the right transistor for this type of an application which is to control a 5m 5050 RGB LED strip with an Arduino. The LED ...
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1answer
39 views

BJT cut-off currents magnitudes and directions

I was reading the datasheet for the 2N3904 transistor (NPN BJT) recently and found out that I couldn't wrap my head around the cutoff current values. For the given conditions, both junctions are ...
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40 views

Loop of Icbo for this NPN common emitter biasing circuit

From what I understand, for an NPN transistor the reverse saturation current Icbo flow can be shown as in the red current loop: My conclusion was that for an NPN transistor the Icbo does not add up ...
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49 views

Why is the current in the main circuit lower with Transistor vs without it?

I'm using EveryCircuit to start studying electronics and I have a question: See image A and B. Why is the current in the A way lower than B? I was assuming it should be the same since the transistor ...
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1answer
110 views

Why isn't my transistor saturated?

Using a BC546 NPN Transistor to trigger an SSR from a current sensor. Sensor to give 1.5-2.7 V out to drive the transistor. SSR requires >= 3 V and uses up to 10 mA. I want the transistor to fully ...
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2answers
113 views

Using NPN transistor as Thermistor emulator

Premium motherboards (Asus Crosshair Hero VII) have T_in 2pin header for 10k thermistor temperature monitoring. Probing around reveals internal voltage divider with ~12KOhm rTop resistor (as per ...
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212 views

How to keep current from draining out the bottom of this push-pull amplifier?

In an earlier question I asked about driving a speaker with a BJT transistor. @Jonk offered a push-pull amplifier design of his own, and @G36 noted its similarity to the JLH amplifier described in a ...
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132 views

Transistor toggle by NPN and PNP - how is it build?

I want to toggle between 2 devices using one GPIO 3.3v pin and powering them with 5v. I thought about using an NPN and PNP transistor, tying up the base and collector/emitter to 5v power supply. If ...
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95 views

Am I right with select of base resistor?

simulate this circuit – Schematic created using CircuitLab I did add the NPN 2N3904 because I want to put on sleep the Arduino. So I need to put LOW the GPIO when goes in sleep. This is a ...
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136 views

Mixed NPN and PNP H-Bridge DC Motor Driver

I've briefly looked at including an H-Bridge circuit in one of my designs and I see that most (if not all) have N-Type transistors (either Darlington or MosFets). This however needs two separate ...
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1answer
40 views

Figuring out the AC equivalent circuit(re model) of a Pre-Amplifier and Tone Control Circuit

I need help figuring out the AC equivalent circuit of this preamplifier circuit. I'm quite familiar with all the simple BJT configurations but this is my first configuring such a relatively ...