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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Why are two transistors often used instead of one?
Many circuit designs I see with transistors use two transistors chained together instead of just using one transistor. Case in point:
This circuit is designed to allow a device with a 3.3V UART to ...
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Transistors in parallel
I want to use several transistors in parallel to control current through a load. This is to distribute the current through the load across the transistors so that individual transistors with a rated ...
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Diode connected BJT instead of a diode
I have read wikipedia and other websites regarding the purpose of a diode connected BJT, but I am not clear on where should we use a diode connected BJT.
Where is a diode connected BJT used? Like, in ...
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Why NPN and PNP in parallel in this distortion pedal circuit?
I've come across a guitar pedal circuit called a "Tube Sound Overdrive". The schematic is shown below. It looks like a typical common emitter transistor circuit with an adjustable bias (RV1),...
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Protecting NPN transistor from negative base-emitter voltage?
I have a circuit that converts 5V RS-232 polarity signals (logical 0 = +5V, logical 1 = -5V) to 3.3V TTL polarity (logical 1 = 3.3V, logical 0 = 0V) using a BC548 transistor.
It forms a NOT gate so ...
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Can the Common Emmiter Amplifier use a PNP Transistor instead?
This is a simple Class A amplifier using an NPN transistor:
Is there a way this can use a PNP transistor, instead (with only 0V and +Vcc, not 0V and -Vcc)? Why or why not?
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Which resistor for NPN transistor base?
Which is the way to choose a resistor for a NPN transistor base?
I want to use P2N2222A as a switch, in a design as shown below. When I have voltage in base (1.8 V), I want a connection to be created ...
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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, ...
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How do I get +5v for loud noise, 0v for silence from Electret Microphone (or other components)?
I have been asking a few questions here to get to a proper one, the initial questions I asked are linked to at the end. I used Fritzing to make up some schematics of my initial thoughts, but at the ...
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Sinking and sourcing current
I have been reading that NPN transistors are sinking and PNP are sourcing devices. I do not really understand this concept. It says current source device connects load to Vcc and current sinking ...
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Understanding a tachometer signal conditioning circuit I inherited
I have inherited a tachometer signal conditioning circuit.
It has an NPN transistor (2N3904) with a Schottky diode (BAT54) between the emitter and the base. It is preceded in the circuit by an LT1017 ...
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Why would I use 2N3904 instead of 2N4401?
2N3904 and 2N4401 appear to be very comparable parts in all specs. 2N4401 has a higher current rating, but otherwise they look to be about the same in price and everything else. Obviously it's ...
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In a circuit being switched by an NPN transistor, do power supply and input need the same ground?
I'm trying to make a circuit that will allow me to switch on a relay that will turn on an LED. However, the relay is rated for 12 V, and I only have an input of 5 V, so I'm using an NPN transistor. to ...
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How protective diode protects transistor from breakdown?
Please, explain the process of breakdown; how exactly this protective diode protects the transistor?
In a Horowitz & Hill book, "The Art of Electronics", 2nd edition, in "Chapter 2 - Transistors" ...
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How can I convert a PNP to NPN transistor?
I have a circuit which requires a PNP transistor.
I only have an NPN transistor.
Is there a way to convert one to the other given that they have the same characteristics (apart from the npn/pnp part?...
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With a transistor (as a switch), does the order of the parts matter?
I've wired up my project(s) similar to how they're laid out in A to control whether or not an LED is on or off. It works fine (as far as I know), but I've seen lots of examples online of circuits laid ...
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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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2N2222A Mismatch between emitter and collector
I am trying to figure out what is going on here.
I have a simple circuit to send current to a brushless fan running at 12V on the high side, using a NPN transistor 2N2222A:
This is the picture of ...
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Capacitor in series with transistor base
I am fairly new to electronics and just had a quick question. I saw the following suggestion for a one shot trigger to wake up an ESP from for example a PIR sensor with one shot trigger and to read ...
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Irregular common emitter amplifier design
Would anyone know of any merits (or demerits) to the common emitter amplifier represented in Figure 1 in comparison to one of a regular pattern (Figure 2)? Thanks.
(The 'DS548' transistor in Figure 1 ...
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Basic electronics: Transistor switch
I am new to electronics. I am reading this book called Practical Electronics for Inventors.
This is a portion about bipolar transistors from the book:
There are two things I don't get from this:
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Control 5v relay through 3.3v GPIO using NPN transistor
I'm not very pratical as I just started learning electronics and I'm planning to make some experiment with Raspberry Pi.
I'm trying to control a 5v relay board that, I think, is made for Arduino, as ...
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Single LED single transistor circuit not working
I was making a circuit with 1 LED and 1 transistor. pretty primarily i was trying to use the transistor as a normal switch. Here is the diagram below.
So, this is an NPN transistor and i connected ...
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A question about Vce of an NPN BJT in saturation region
Below is an NPN transistor symbol and the voltages at its terminals are Vb, Vc and Ve with respect to the ground:
I read that: during the saturation the Vce = (Vc-Ve) settles to around 0.2V and the ...
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Why is my transistor accepting power from a base?
I have a transistor (NPN, to be exact it's a SS9014). Whenever I run 4.5 V through the base, connect a resistor and LED to the emitter and connect the LED to ground, the LED has a faint glow. Why is ...
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Confused about transistor operation
I'm trying to use a BC108A (datasheet) transistor as a switch for a 12V power supply using the 5V digital out pins on an Arduino Uno board.
I have connected the collector the 12V supply, the base to ...
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Why is the load in an NPN transistor switch located in the collector circuit?
I made a simple transistor switch. I read the theory and in many sources I saw that the load (with an NPN transistor as a switch) is connected to the collector circuit, not the emitter circuit (...
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Help needed optimising simple current limiting circuit
I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I have started using a circuit like the one found on this ...
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How do I check a BJT transistor if it is still functional?
Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective?
simulate this circuit – Schematic created using CircuitLab
Say for ...
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Is a large hFE value a sign of damage?
I have been testing a couple of BFY50 transistors that I salvaged using my multimeter. One of them reports an hFE of ~109 (this looks consistent with the data sheet value of 112). The multimeter ...
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Simple circuit works with BC547, but not with 2N3904
I am following a very simple schematic which is a NOT gate with a push button as input. The output is used to drive the base of a second transistor that turns on an LED:
This circuit works perfectly ...
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How do RF broadcast towers switch so much power so quickly?
Edit: I modified numbers below for a "licensed 1000 kW ERP channel", for which total true radiated power (being in a pancake shape since there is no need to radiate up into space) is ...
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High side or low side LED driver with NPN BJT? Which is better?
I think the B configuration would be more stable in temperature variations, anyhow I would like to hear some good suggestions on which configuration should be used and what will be the benefits of ...
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Make adjustable mosfet constant current source
I want to modify this circuit below so the current can be trimmed.
The problem is the variations in base-emitter voltage of the NPN transistor. According to datasheets, it is between 0.55V and 0.7V ...
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Understanding a 2 transistor oscillator?
I asked a question here about why I was getting a sawtooth wave from a two transistor oscillator. While that question is answered, I don't understand how the circuit produces oscillation in the first ...
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How does the collector emitter relationship work with a transistor?
So,
I'm not understanding how NPN transistors really work in this scenario. In this image, I
have highlighted what I understand to be the collector and emmiter. My understanding is
that power ...
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Switching a current with an NPN transistor and a P-MOSFET
Just learning about transistors and I'm trying to clearly understand how to apply them for basic switching, in terms of the two standard cases, i.e., Active HIGH behavior and Active LOW behavior. For ...
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Why do we assume VGS<Vth and Vds>0 for a mosfet in cuttoff and Vce>0 for a BJT in cutoff?
The devices below are both n polarity devices, the BJT is a NPN and the MOSFET is a NMOS.
For the BJT in cut-off, why do we have to assume \$V_{ce}>0\$?
For the MOSFET in cut-off, why do we have ...
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Why the base current decreases automatically?
Given this circuit:
simulate this circuit – Schematic created using CircuitLab
I don't understand why, when simulating it by increasing parametrially the V2 from 0V to 12V keeping V1 constant, ...
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Why does this NPN transistor operate differently if it comes before the switched element?
I'm simulating turning an LED on with a transistor switch in LTSpice. To my bewilderment, the current through the LED in Circuit 1 is ~51 mA and the current through the same in Circuit 2 is only ~6 mA....
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NPN transistor resistor from base to GND. Is this useful?
I have a circuit where many NPN BJTs are interfacing 3.3 V GPIOs with higher voltage circuitry. Each application has a similar setup to the image below (resistor R422 is what's in question). I did ...
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How to determine whether a given transistor is NPN or PNP?
If I have a device which I know is a BJT transistor but I have no other information, how can I determine whether it is NPN or PNP and which pins have C, B & E functionality?
user286208
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TIP120 Transistor + Solenoid Failing Randomly
I am using TIP120 transistors (controlled by 74HC595 shift registers) to control 12VDC, normally closed solenoid valves. Everything is working in short-time tests however when left overnight, some ...
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2N2222 as a switch
I'm looking to drive a relay on a 5V rail from an Arduino 3.3V pin. Obviously the Arduino I'm using doesn't have the voltage to drive the 5V relay, so that's where the 2N2222 comes in. To test out the ...
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For this NPN current source circuit, why is the simulator indicating such a high base current?
simulate this circuit – Schematic created using CircuitLab
Why is the base current into Q1 so high according to the simulator? It is higher than I expect.
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What (if any) is the leakage current through a NPN (C-E)?
So I have a circuit where I need the current consumption to be low. Therefore I am using a 10M\$\Omega\$ resistor to 'pull-up' the pin on a chip which will need to be switched between high and ground ...
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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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What is the purpose of connecting the collector of an NPN to the base of another NPN? [duplicate]
In the circuit below, in the section inside the green circle,
it seems there's no purpose for connecting the NPN transistor's collector, to the base of the other NPN transistor on the right.
...
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Good NPN configuration vs bad configuration
Let me try this post to see if I can properly ask the question.
I have the common emitter configuration which works for me, the math (Ie = Ic + Ib) works. The load is in series to the collector. And ...
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74HC595 Rows/Columns to drive LED matrix
Let's say we have one 74HC595 and we want to light 16 leds (common anode) connected as a 4x4 matrix exactly as in the following picture :
So, 4 first outputs to controls 4 rows.
The remaining 4 ...
