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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BJT common emitter output conductance
I constructed in multisim a common emitter circuit from the following diagram
where the lower Keithley is used to supply VBE and the upper Keithley is used to supply VCE.
I obtained the IC- VCE ...
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Sticky/Intermittent Relay Driven by MCU and NPN Transistor
I have an MCU (1.8 V logic levels) driving an NPN transistor to turn an relay on/off. The relay has a 12 V DC coil with resistance of 1028R per datasheet. This would require a current of 12/1028 = 11....
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Transistor resistor calculation help (design revision 1)
I posted my original design yesterday and got many comments about my errors. This is revision 1 of my design. I am now pretty sure I have the load resistors calculated correctly, but still unsure ...
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Transistor Resistor Calculation
I am new to electronics so I'm not too sure about how I should be calculating the base resistor to use in this circuit.
I think the load resistor is calculated correctly (data sheet at bottom for ...
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When switching an LED with a transistor via a microcontroller, do I have to worry if the load supply voltage is higher than my microcontroller logic?
I want to turn a white LED on and off via my microcontroller GPIO. The ESP-01S board that I have uses an ESP8266 chip, which has a limit of 12 mA GPIO output current. However, I want to drive this LED ...
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NPN BJT Operation - What does it mean for the Collector - Base junction to be reversed biased?
According to this screen grab the Collector Base junction must be "reversed biased". I seem to be confused about the meaning of that. I thought that the Collector needed to be at a higher ...
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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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Op-amp LED project
I'm trying to understand this circuit, but I'm having trouble understanding what the second op-amp block does.
I understand tha the first one is an oscillator controlled by a trimpot (RL,) but the ...
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Why isn't the NPN diode model two diodes connected in series?
I don't understand how we can model an NPN transistor with two diodes with their anodes connected. Shouldn't they be in series, with the base being in-between the diodes? An NPN transistor is in ...
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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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Is this a correct way to use an NPN transistor to disable a push button?
I'm using the Raspberry Pi's GPIO to display some information in a LCD (using I2C) and to enable the usage of a few buttons to navigate through the LCD menus. There's another button, the one I'm ...
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How does this transistor behave as the base voltage is increased?
Consider this transistor. How do the voltages Vb, Vc and Ve vary as we increase ...
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Why would an emitter follower be DC-coupled to its input?
In my experience, an emitter-follower amplifier is usually AC-coupled to both its input and output:
However, I recently came across such an amplifier which is DC-coupled - the capacitors C1 and C2 ...
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NPN transistor replacement verification
I am trying to replace several transistors on my PCBs due to chip shortages. One such unit is a particular NPN transistor datasheet I cannot get my hands on these little guys anymore. But I figured ...
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PNP- NPN light flasher
I understand that
R1 and R2 make a voltage divider.
initially Q1 is not conductive, so is Q2?
initially C1 acts as short circuit, so flashes the light L1 for a moment?
Please correct me if wrong.
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P Channel MOSFET gate controlled by N Channel MOSFET (rather than NPN). Crazy?
I needed a generalized circuit that would switch on/off any device on the Vcc side with varying voltage (3.3 to 24 V) and current (0 to ~10 A). A P Channel MOSFET is an obvious choice, but I didn't ...
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Relay does not switch off
I have what I thought was a simple relay circuit but the relay is always on.
This is the part of the project that is not working
Q5 never switches off.
To simplify it further I removed the relay and ...
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identify transistor
Does anyone know of a website or online tool to help identify a transistor-like component by its markings?
For instance, one cracked and from the pieces, I can't be sure what it used to read (partial ...
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Can I use a BC338 in this application?
I want to build this FM transmitter that runs on 1.5-3V.
I've got 2 questions so far:
Can I use a 2N2222A NPN in this application? (I think I can but want to double check.)
How can I calculate (or ...
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How to calculate base voltage and current for NPN transistor required to drive a P-channel MOSFET gate
I'd like to use a P-channel MOSFET as a on/off switch. I can't pull the gate down directly from my controller because the voltage of the load is 12v, thus I have to use another transistor, as far as I ...
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Transistor collector emitter saturation voltage
I am trying to choose a transistor to use in a current mirror to prevent thermal runaway of parallel LEDs (yes I have to connect them in parallel. I know connecting in series or using separate ...
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How can the transistor be in the cut-off region?
Imagine we have an NPN transistor and the base voltage Vb = 0V. How can the transistor be in the cut-off region?
I've started by assuming it to be in the active region and then calculated the emitter ...
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Tachometer frequency problem
I have an NPN tachometer sensor. I want to measure the rotation speed of a three phase motor, but the output frequency of the tachometer changes. For example, if the actual value of the motor ...
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Help Needed with LTSpice Multistage Cascode Simulation
I'm using this online calculator to get -50 gain for a cascode amplifier:
https://www.daycounter.com/Calculators/Cascode/BJT-Cascode-Calculator.phtml
However, I failed to duplicate the value in ...
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How to modify this circuit so that the second LED turns off completely?
Circuit simulation is here
There are two parts to this circuit. The first part is a switch that is either floating or grounded, controlling a large number of relays via pnp transistors. (Many relays ...
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How can I solve this simple BJT circuit?
Looking at this circuit (first circuit):
Choose a value for V2 between 0V and 10V. Then how could we know the IB, IC, IE, VB, VC, VE? Can we solve it by hand (by hand means the value IB, IC, IE, VB, ...
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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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Totem pole driver topology (inverting amp)
Hello guys this question is regarding a gap in my knowledge regarding transistors specifically the driver of the totem pole configuration. Based on the following figure
And these results here:
When ...
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How to choose a transistor for PWRKEY on SIM808 design?
I am using a 3.3V digital output signal from a microcontroller.
The design documentation suggests using this circuit. How do I determine the transistor that I need?
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What is the purpose of the D4 diode between base and emitter of PNP transistor?
I am having problem with understanding the purpose of the Q7 transistor. .
The anode of the D4 diode is connected to the base and cathode - to the emitter which makes Veb = -0.7V. This will always ...
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Saturation for emitter follower
How can a transistor connected in emitter follower configuration be driven into saturation?
I know that for saturation, the base voltage should be greater than the emitter voltage, but also than ...
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use NPN as a switch between nets that don't have a voltage difference
I'm trying to use an Arduino with a 2n2222 npn transistor to replace the functionality of S1 in this diagram. This is the schematic for my TV remote. I want to replace the physical switch with a ...
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Four digit seven segment display using a 3904 BJT
I have a temperature circuit that uses a common anode seven segment four digit temperature display.
It uses a PIC12F1572 to read the temperature from a one wire device and shift the numerical bits to ...
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NPN on top of L298N H Bridge
I understand how an H Bridge works, but the common ones use pnp transistors on top and npn on bottom. In L298N's datasheet it is attached this circuit and I just can't figure out how the Vs is going ...
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Why isn't my common emitter amplifier working properly?
I simulated this common emitter amplifier in LTSpice:
However, instead of an amplified sine wave, the voltage at the output looks like this:
Would someone be able to explain why this is happening? ...
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How can MOSFET drain be used as ground for a load?
I'm trying to understand how the schematic from this github repo works. It uses an RTC to turn on an arduino, via a npn transistor and a mosfet.
I'm novice with electronics, so this might be a ...
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How do I solve Vb or Ib of a bjt with a base transistor?
The problem I run into is I don't know what Vb, Ve, or Vc are. So I don't know where to turn. If i knew Vb (or Ve) I would use Vbe = 0.7 to solve the other and then I could solve for the current ...
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Power output of a CC amplifier
I've been learning about electronics from the book Electronics Fundamentals, and have just finished the chapter about BJTs. Decided to put the newly gained knowledge to use and designed the following ...
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Why does the led turn on in the following circuit?
So i have connected a transistor as shown below where the base of the transistor is connected to the negative of the power source and the emitter is connected to the negative side of an led and the ...
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how to find gain of this complicated circuit?
I am having trouble with the following circuit. This circuit is AC model of Colpitts oscillator designed with NPN type BJT transistor. I am trying to find loop gain and check if it meets Barkhausen ...
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How can we find the voltage gain of a BJT circuit if the Vin and Vout are on different transistors?
I am trying to find the voltage gain of the circuit below. I drew the small-signal model for it (shown below). I know the formula for finding the voltage gain of a common-emitter BJT with and without ...
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Ultrasonic sensor ON/OFF switch with transistor
I have an ultrasonic sensor (JSN-SR04T) connected to an Arduino. In order to achieve low power consumption i decided that i want to switch the Ultrasonic sensor off for 8 seconds intervals in between ,...
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Are these scope traces normal for a reverse polarity LED hooked up to an NPN transistor?
I've been trying to make some cheap light sensors using some coloured LEDs and am using the schematic below. The idea is to hook up a bunch of LEDs (Red, Green, Blue etc.) to try and get an idea of ...
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Is saturation region defined for a "given" collector emitter voltage?
I have seen the traditonal saturation regions graphs (attached). The graph gives the impression that there is a huge region which is saturation region. Shouln't the saturation region be for a "...
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Does the collector voltage have to be greater than the emitter voltage by few tenths of a volt for an NPN transitor
For an NPN transistor, does the collector voltage have to be greater than the emitter voltage by few tenths of a volt for it to be in active state? If yes what is the reason?
Also it says greater by a ...
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Linear voltage regulator dropout voltage
I have a question regarding on linear voltage regulator. The pass element in the linear voltage regulator can be NPN or PNP transistor. If a Darlington pair is used as the pass element, the dropout ...
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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?
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What is the current flow logic of this NPN configuration [duplicate]
For a switch i need to put the transistor in cutoff to OFF and saturated for ON as shown in the lecture bellow.
My input is a voltage source i need to control the base current to make the collector ...
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Understanding the phototransistor
I am trying to learn how a phototransistor works, and I have made a schematic to show how I understand the photo-diode and NPN transistor to be linked in a phototransistor.
I think that when light ...
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Understanding how a NPN transistor works
I have been trying to understand how an NPN transistor works, specifically in the case of a photo-transistor.
As far as I can tell, it should be something like this:
I don’t understand how current ...