Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

857 questions
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How to calculate a transistor response time to a square wave?

My objective is to learn how to predict the output to a sqaure wave given R1, R2, R3 and Q1 datasheet (not specifically the 2N3904) without using SPICE or any other software I was looking on google for a good source but could not find something…
Charls Diven
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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 circuit, I figured I'd substitute an LED for the…
Jon Angliss
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Why shouldn't you use the emitter of a BJT NPN Transistor as a current source?

Several times here on the EE Stack Exchange, I've seen people say not to connect a load between the emitter of an NPN transistor and ground, but instead connect it between the power source and the collector. In that case the transistor is a current…
Duncan C
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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 a snapshot: I am looking at the line labelled…
user1700890
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Transistor not triggering

When the base side of the transistor giving a voltage 0 V, across the collector side getting 2.3 V and if give to the base side only voltage 3.0 V, the collector giving voltage 2.9 V. It is not decreasing why? transistor NPN MMBT3904. Resistor 2.2…
Imran B
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Increase the voltage in a simple NPN circuit

I'm building the circuit described here, but I need to tweak it a little. I need a stronger magnetic field from the coil to move a bigger 'swing'. So I want to increase the number of turns on the coil, but then I'd also need to increase the voltage…
thomas clssns
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Using +4V output, to trigger an npn transistor operating on +12V

In a +12V circuit, I am trying to use a proximity sensor, which works on +5V and its output is +4V, and goes 0V when triggered. Using a L7805, I get the +5V for the sensor supply. However, I try to use its output to trigger a transistor operating…
George Kladouhas
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Remote control led has 3 volt power source output I need it to switch on a 12 volt power source to power led array

I have a LED candle that runs on two AA batteries which total 3 V. It already has remote. I want that 3 V output to turn on a 12 V battery supply to a LED array. I am trying to use an NPN transistor for this: am I doing right? What else can I…
kevin
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Help needed... NPN current flow with 0v at Base

I'm having a head scratcher: simulate this circuit – Schematic created using CircuitLab In my mind this should work flawlessly. The 5v/GND through R1 to the base of Q1 is controlled by a microcontroller (but for testing I am literally connecting to…
Chris Robertson
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Base resistor value on 2n3904 used as a switch

I am well aware that similar questions has been asked and I have read a lot of them. I still need to ask this before I loose my mind :) I want to, and have also managed to use a 2n3904 as a switch/button, where I use a digital pin connected to the…
Sourcery
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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?
Arturo Veras
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How do I connect a NPN transistor so it operates in the saturation region?

I am learning about NPN transistors and I could not find how to connect the transistor so it operates in the saturation region.The circuit that I have made works in the Active region,because when I run the simulation the current on the emitter is…
ROBOTICS
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Help me understand NPN transistors, circuit does not work

I'm working on a project where I need a transistor. I want a Attiny85 mcu to turn of and on a relay. But the current in that chip is to low so I figured out I have to use a 2N2222 NPN transistor as a switch so the relay could draw current from the…
fUrious
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NPN as toggle switch

I have a very old printed circuit board here that is used to control 2 pneumatic cylinders. There are 8 solenoid valves that control if the air goes in or out to a side of the cylinder. Now the printed circuit is old and needs to be replaced, so I…
Roger Far
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Using NPN-Transistor as switch not working

I have following schematic: simulate this circuit – Schematic created using CircuitLab But the motor is not working, the NPN-Transistor does not seem to let any current through. What am I doing wrong? the transistor does work, I checked, but there…
Daniel
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