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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 current from Emitter to Collector enabling amplification and switching.

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Designing circuit parameters with NPN-PNP transistors -LTspice simulation

Below is a part of the circuit I created to drive the MOSFET (it includes level shift, power stage etc.). Datasheet of 2SC2411K: https://fscdn.rohm.com/en/products/databook/datasheet/discrete/...
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Typical output characteristics table of an NPN transistor

The Ic - Vce table for the 2SC2411K transistor is given below. As it is known the right side of the table represent the breakdown region. That is, does the Vce > 5 V region enter the breakdown ...
Mhan's user avatar
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Calculation of transistor values using hFE

I provided a very simple NPN transistor set up and hFE values as shown below. 2N2222 datasheet I am trying to calculate parameters such as base current, collector current, Vce using hFE (beta). The ...
Mhan's user avatar
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LTspice simulation of Class B amplifier

In the 1'st picture below I provided the amplifier circuit diagram. The 2'nd picture is showing the base signal of Q5 (green colour) and Vce signal of Q5 (blue colour). It is working as it is expected....
Mhan's user avatar
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Driving Mosfets using NPN - PNP transistors in Ltspice [duplicate]

I sent the SPWM I produced to the transistor as seen in the diagram below. pwm frequency 10 kHz. As seen in the 2nd picture, PWM-A works fine. As seen in the 3rd picture, I shared the unzoomed version ...
Mhan's user avatar
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Output of TIP122 drops when connecting a load

I have built this circuit: (the components here are labeled wrong LM317LZ is LM317T and TIP122G is TIP122) When there is no load the output of TIP122 is 10V-20V (when adjusting potentiometer) which ...
Raudonkepuris's user avatar
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Battery Charging Circuit - What is the operational analysis of device Q1?

simulate this circuit – Schematic created using CircuitLab V1 is a 24 volt dc 210 milliamp power adapter. V2 is a 14.4 volt nominal nicad battery in a handheld vacuum. V1 is almost 30 volts open ...
SystemTheory's user avatar
-1 votes
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Used Transistor as Switch LED

I designed simple circuit using transistor as switch for my led. I used npn transistor. The input voltage is 46V. The current input is 15mA. My question is my circuit is correct or not?
Kim's user avatar
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What is this NPN circuit doing?

I'm trying to make a mod to a board from a device I have, and I'm trying to decipher what a particular circuit on it is doing. I'm somewhat of a hobbyist in circuits, but I'm not 100% sure whats going ...
SenPi's user avatar
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What happens when the CB junction is in forward bias and the BE junction is in reverse bias in an NPN bipolar transistor?

What happens when the CB junction is in forward bias and theBE junction is in reverse bias in an NPN bipolar transistor? I thought of two possibilities: The NPN transistor acts as it is but in ...
Qwe Boss's user avatar
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NPN transistor as a switch configuration

I have a npn transistor configured as a switch which is normally on and at times I have it switch off and on at 7Hz-8Hz, with R1 5.10k and R2 100k and 0 V to 5 V MCU pin and max \$I_C\$ current from ...
Citi's user avatar
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ESP12 to switch computer power

Hi all! I'am trying to use an ESP12S to turn a desktop computer on/off remotely, using a NPN 2N2222 transistor, while also trying to keep the physical power button working. Much like this project: ...
SnackK's user avatar
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2 answers
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Does a negative base current in BJT npn mean that the operation mode is Reverse Active?

Given Vce = 2V, Ic = 1.7mA, and Ie = 1.6 mA, I used KCL to determine that Ib = -0.1 mA. Does this mean that the BJT npn is in reverse active mode?
user364328's user avatar
2 votes
2 answers
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How can I calculate the base current required for my multistage connected PNP transistor to obtain an obtain an output collector current Ic = 1.5A?

I need to design a circuit that provides an output of 11.5V with a current of 1.5A. This output is drawn from a TIP42 PNP transistor. The transistor gets its base input from a NPN2222 transistor. The ...
Coding247's user avatar
2 votes
3 answers
384 views

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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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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1 answer
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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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Iₑ current equation in relation to saturation current for saturation region in an NPN BJT

In the saturation region for an NPN BJT, $$I_C = I_S\cdot e^{\frac{V_{BE}}{V_T}} - I_{SC}\cdot e^{\frac{V_{BE}}{V_T}}$$ Since \$\small I_C\$ is approximately equal to \$\small I_E\$, will \$\small I_E\...
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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
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1 answer
66 views

Using an NPN to detect high voltage and switch a battery circuit

I've done some simple PCB's but am not a real electronics designer so forgive stupid mistakes or stupid questions. I'm trying to detect a voltage range between 1-50 volts (VIN) as digital 'on' and ...
Oscar K's user avatar
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2 votes
2 answers
141 views

I designed an opamp, any additions on how to make it better? (Closer to ideal opamp)

I'm not very good at electronics, but after learning for a bit, I designed a bare minimum opamp which has a differential amplifier and a Darlington NPN amplifier. Here is a picture: I thought about ...
TheAmplifier's user avatar
13 votes
4 answers
3k views

What are the tradeoffs between NPN vs PNP power transistors?

I'm working on a linear power supply design leveraging the uA723 regulator and I need power transistors to meet the current requirements (~2-3A). When looking looking through the regulators datasheet, ...
david's user avatar
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1 answer
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Determining which resistors to use in a common-base amplifier

The assignment is to design a common-base amplifier from a supplied schematic, and quite frankly amplifiers are a significant weakness of mine. Given: Small-signal voltage gain A_V≥50 V⁄V Input ...
StarSword's user avatar
0 votes
3 answers
130 views

Pulling pin low through PNP BJT?

I'm using a battery charger/buck regulator IC that turns on if the pin named "shphld" is momentarily pulled low, and turns off if the pin named "shpact" is momentarily pulled high. ...
FloydPage's user avatar
1 vote
1 answer
118 views

NPN Transistor Base Current Calculation from Beta, Vth, and Rth

In this answered question regarding a common emitter NPN Transistor.... NPN Transistor common emitter calculation I am struggling to understand the section "Assuming Active Mode" ...
Jeffrey Edward Messikian's user avatar
1 vote
3 answers
169 views

Why doesn't this NPN transistor AND gate work?

I am trying to form an AND gate using 2 NPN transistors, but the LED lights up when I turn on the right switch and the left switch doesn't make any change. Can someone please point out the problem?
Aland's user avatar
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2 votes
1 answer
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PIR sensor circuit

I am designing a PIR sensor circuit to detect human movement. I am supposed to display movement using an oscilloscope (the response from this PIR sensor.) I have used the following circuit but it does ...
user355274's user avatar
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1 answer
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Bipolar NPN transistor does not work as expected in simple circuit

I need simple button in Raspberry circuit to force wake up on GPIO3 which is shared with I2C and shutdown on GPIO4. So I have cascade of inverting NPN bipolar and MOSFET. The circuit is pretty simple. ...
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NPN Transistor Circuit Diagram

I have npn transistor circuit and want to change the input from 48V to 12V. My question is can i used same circuit digram using same npn transistor (S8050) for input 12V by changing the R1 and R2 ...
Kim's user avatar
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3 answers
153 views

Using the PLC output to mimic a NPN sensor as the input to a device

I got a device which has a connection to a NPN proximity sensor, it'll do something when the sensor is being trigged. Now I remove the sensor, using a PLC(24vdc) to do the job of sending the signal to ...
castiel's user avatar
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2 answers
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How does this oscillator circuit work? Inductor phase

I simulated in it LTspice software. The voltage waveform across capacitor C4 was sinusoidal. I know its some kind of oscillator but don't know how it's operating? I think the reason behind center ...
nitin shrestha's user avatar
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How does this oscillator circuit works? [duplicate]

When the switch is closed, the current flows through the resistor and because of it high amount of current flows through lower portion of the coil and led turn on. In the meantime, because of the ...
nitin shrestha's user avatar
2 votes
3 answers
326 views

How does this oscillator circuit with a transformer work?

I know it is an oscillator circuit but I don't know how it works. This circuit is supposed turn the LED on and off continuously. Can you please explain it to me? The star sign in the figure is not ...
nitin shrestha's user avatar
0 votes
5 answers
2k views

Output characteristics of a BJT

While plotting the output characteristics of a CE configuration, the graph between VCE and IC, it shows that when VCE=0,IC=0 My doubt is whether VCE=0 means we are shorting collector and emitter or ...
Aami's user avatar
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6 answers
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STM32 12V input via NPN transistor

I'm trying to sense a 12V input on a STM32 microcontroller. This is the schematic I came up with: When I short the pins of CN1 the STM pin goes LOW and I can read correctly that there is an input. ...
C.C.'s user avatar
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2 votes
1 answer
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How do I work around NPN transistor leakage current?

I am trying to use NPN transistor to switch a 12 V LED strip. Even when there is no voltage applied to base of the transistor the LED strip still flickers a little. I suspect this is because of NPN ...
Petr Peller's user avatar
3 votes
1 answer
522 views

Incorrect current direction in an NPN transistor

My circuit is below. It has an NPN transistor. In NPN transistors, the current is supposed to flow from collector to emitter (from positive to negative), but CircuitLab shows negative current. Here is ...
user1700890's user avatar
2 votes
2 answers
289 views

NPN (2N2222) transistor as a switch replacement for a RF garage control

I'm looking to "replace" a physical keypress on a garage door remote control (RF) with a pulse (HIGH state) from a Wemos D1 mini 3.3V pin. The remote control is this one I measured the ...
vazquezjm's user avatar
0 votes
1 answer
134 views

NPN transistor won't switch off in boost circuit

I'm designing a boost circuit to generate ~150V from a 1-4 cell lithium battery. It doesn't need to supply a lot of current; I just need high voltage. Using a 4 cell battery with full charge (16.8V), ...
SMMB's user avatar
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1 vote
1 answer
239 views

How to turn an LED on in an inverter circuit

I am currently trying to build an inverter circuit which turns on an LED (on a simulation before building it physically). I am using an 2N3904 NPN transistor, 5V voltage sources, a 220k and a 47k ...
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NPN Transistor calculation

I want to find the value for \$R_1\$ and \$R_2\$. Is my calculation right? Assume \$h_{fe} = 120\$, \$V_{ce} = 25\$.
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Different applications of NPN and PNP transistors in open collector circuits [closed]

Dear electronics enthusiasts, I recently encountered an interesting problem in electronic circuit design, related to the application of NPN and PNP-type transistors in open collector circuits. My ...
FredMorgan's user avatar
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2 answers
200 views

High side NPN and PNP switch

I have a high-side switch using a PMBT2222A NPN SOT23 and MMBT2907 PNP. Now my concern is if my configuration not beyond the specifications of the PNP transistor like not going out of their max ...
Citi's user avatar
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1 vote
2 answers
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How is R3 drawing 0.6 mA current?

How is it that R3 draws 0.6 mA current in the circuit described below? The "divider" formed by R2-R3 may be confusing: R3's job is to keep Q3 off when Q2 is off; and when Q2 pulls its ...
user232591's user avatar
-2 votes
2 answers
142 views

How to turn-on NPN transistor? [closed]

Connecting base to high state from MCU Transistor: BD239C Collector-emitter is powered by 12 V 2 A and resistance is 660 Ω, 12 V / 660 Ω = 0.018 A Base is powered from MCU output by 5 V 0.2 A and ...
Jakub Kutrzeba's user avatar
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1 answer
120 views

NPN Relay Driver Problem

I've designed what I thought would be a simple relay driver circuit to drive a relay with a raspberry pi GPIO pin (which is pulled down with a 50K resistor internally). In the circuit diagram, pin 6 ...
Matt's user avatar
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Simulating BJT 2N2222 in LTspice. 5 mA collector current when B and E shorted

I am simulating NPN 2N2222 in LTspice. When I short base and emitter, the collector has peak up to 6 mA. Should not it be in terms of nA when there is 0 V between base and emitter? Can you please ...
Kurt Müller's user avatar
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LMC555 delay off timer, M20 motor drive, updated

The goal is to either just give a signal to the motor with momentary switch, or turn on the toggle switch, let 3.7V motor run for a couple of seconds before 440uF is fully charged, after which voltage ...
Domenico's user avatar
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2 votes
2 answers
370 views

N Channel MOSFET reverse voltage protection proposal

While learning how to make a buck converter, I realised that using P channel mosfets for reverse voltage protection is one of the best ways, but I think it could be better using an N channel using the ...
Mito's user avatar
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1 answer
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Correct use of a ULN2803A

Did I wire up correctly this ULN2803A? I am trying to use it to power an RGB LED Common Anode strip ith a length between 50 cm and 1 meter, and a 24 relay with an Arduino Mega 2560 Thanks in advance }...
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