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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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Switch resistor with n-channel MOSFET not working

So I try to amplify a photodiode signal with an operational amplifier. As I want to amplify two signals (1 for a high-intensity light and 1 for a low-intensity light) I sort of need to design a ...
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Why is Ic constant in the plot of Vce vs Ic in a common emitter NPN transistor (in active region)?

In this plot, when \$V_{ce}\$ increases in the active region, shouldn't \$I_c\$ also increase as more electrons are getting diffused into the collector? Then, why is it that for a large range of \$V_{...
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Reset pin of the 555 timer is not effective when connected to ground through an npn transistor

I am building a fire alarm circuit based on a 555 timer and an NTC thermistor \$R_T\$. The circuit is shown below: I computed the value of \$R_1\$ such that the voltage at the base of the ...
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NPN - Emitter Connected to Base

simulate this circuit – Schematic created using CircuitLab If the output(Y) of OR gate is connected to one of its input(B) then output will always be 1 after we set input A to 1 even if we ...
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40 views

2-stage BJT CC-EC amplifier [closed]

Using proteus I designed this amplifier: But I got this result: I don't know what is the problem in my design. I've been changing the values of the linking capacitors but didn't get any result.
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59 views

Need help with three-stage transistor amplifier in LTSpice

I am currently attempting to design an amplifier in LTSpice for an E1 project. My professor tends to emphasize analysis of these circuits, so he hasn't really given us any kind of a design process to ...
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75 views

Which region is the transistor operating at?

PNP and NPN transistors in the circuit have identical Is values. Based on the PNP transistor is connected to a DC voltage source. k = 1.38064852×10-23 J/K qe = 1.60217662 ×10-19 C Is = 0.69 fA at 17°...
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52 views

Brake DC MOTOR circuit

I have a DC motor that is controlled with an npn transistor with pwm. Everything works fine. I want to brake the motor instantly. I tried to short the terminals with another pairs of transistors but ...
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Transistors why do they amplify current?

Ok guys I can't understand a thing of the Transistor here is the scheme: My teacher said that when I put 0,7V on the base the PN junction between Base and Collector is direct polarized so the whole ...
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1answer
51 views

Need help understanding PNP Base into NPN Collecter circuit for LED Array

I am a novice in circuitry and I'm trying to make an 8x8x8 LED Cube using an instructables guide for a school project. I have ordered all the parts and was testing the grounding circuit for each layer ...
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1answer
37 views

Is resistor needed to drive NPN Transistor from EEPROM

I am using this EEPROM in read mode: http://ww1.microchip.com/downloads/en/DeviceDoc/doc0270.pdf And am using this transistor: https://www.onsemi.com/pub/Collateral/P2N2222A-D.PDF I need my EEPROM I/...
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139 views

Arduino - Using NPN transistor as a switch to pull-up/down analog pin

Let me start by saying that I am not an EE, and my knowledge in Electronics is basic, so please bear with me and be patient if, initially I am bending a few rules. In Epee fencing, a touch is awarded ...
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49 views

Driving LED with 555 timer and BC639 transistor

I am trying to produce an LED dimmer circuit using a 555 timer circuit and a BC639 NPN transistor. I know there are better transistors that would suit the task better, but the BC639 is what I have to ...
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1answer
60 views

Current spikes on rising and falling edge of NPN BJT switch

I am simulating a simple NPN BJT switch for PWM in LTspice, and I observe some current transients on the rising and falling edges that I do not understand. The circuit is here: Picture of the falling ...
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69 views

NPN transistor numerical

I think the steps will be STEP-1: \$V_x - V_{BE} = I_B\times R_E\$ STEP-2: \$I_B = I_{ra} - I_{rb}\$ STEP-3: \$V_x = V_{in}\times R_B/(R_B+R_A)\$ Please tell me i am correct or not??
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Is this discrete mosfet driver ok?

I've come up with this mosfet driver, mostly inspired from other designs using push pull configuration. It consists of four transistors (1 pnp, 3 npn) + an optocoupler. Its intended operation is ...
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3answers
38 views

For MMBT2222; How to get hfe value to calcluate minimum base current to drive transistor in Saturation?

If my collector current VCC = 3.3V & Ic = 31.82uA then how to calculate minimum base current is required put transistor in saturation mode? Depending on it I will calculate base series resistor ...
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Transistor as switch (in Saturation mode) - Why transistor saturation appears early with increase in collector resistor

This image is a simulation of a 2N2222 transistor as a switch to level shift 12V I/O signal to MCU compatible 3.3V I/O input. Simulation is done on LTSPICE XVII with DC sweep analysis of V2 (12V) (...
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Over-current sense

I am using a circuit shown below. it is designed to sense 1.5 A whenever the load takes current >= 1.5 A. Rsen senses the related voltage and activates the transistor. Here I use a Rsen = 0.46 R(0.7V/...
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53 views

MMBT2222 Datasheet doesn't mention maximum base current. How to calculate it?

The MMBT2222 Datasheet doesn't mention the maximum base current. How to calculate it? So that design should not exceed it. I want to use it for switching in common emitter configuration; where the ...
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46 views

Making a DC motor turn in saturation and cutoff modes of an NPN transistor

simulate this circuit – Schematic created using CircuitLab So I have a DC motor that should turn with light on LDR and should stop when I cover LDR or turn off the lights. Basically the ...
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4answers
70 views

Non-inverting output of transistor circuit (at NPN base) is 0.69V max. why?

I tried to make a simple NPN transistor inverter so that I can use the strobe line of the parallel port to store data in two separate flip-flop IC's. (74HC174 and 74HC574) The IC that data will be ...
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1answer
115 views

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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57 views

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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66 views

Reduce active region of NPN transistor

I've got a small LED garden lamp, battery operated, that turns on with a switch. I am currently trying to use a photoresistor that I have to make it turn on when it gets dark (so I don't have to ...
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63 views

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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Calculating collector current of NPN BJT with LED & resistor

I've been trying to wrap my head around the current I measured through the collector branch vs. the expected calculation for collector current and believe I have a knowledge gap in what to do. The ...
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1answer
46 views

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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1answer
57 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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3answers
100 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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66 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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1answer
98 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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1answer
102 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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56 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
132 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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95 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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1answer
141 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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1answer
65 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
119 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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1answer
66 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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4answers
130 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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2answers
65 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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1answer
70 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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3answers
92 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
93 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
115 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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78 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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2answers
52 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 ...