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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NPN transistors, LED strip and Arduino

I'm trying to control an LED-strip with an Arduino like an 8x8 matrix with a common anode (pic 1). I put 2 NPN-transistors in the circuit and a LED-strip between them. The first transistors in pic 2 ...
5 votes
1 answer
147 views

What is the purpose of these transistor pairs

This picture is part of a circuit designed to measure capacitance. The control circuit would apply +12V or -12V on "DTR pin 20" and the two resistors give a minimum and maximum voltage ...
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1 answer
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Operating point for high current transistors

I'm a neophyte self-thaught learning electronics. I'm trying to amplify a DC current from a little less than 1 to 8 A using an NPN transistor. Currently I'm trying to figure out how even could I ...
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ESP32 opto-isolated relay board not working - PC817 opto-isolator, 2N3904 NPN BJT and SRD-05VDC-SL-C relay

I have just finished soldering my "custom designed" ESP32 PCB board that I'd like to use for management of 6 x 24 Vac irrigation valves. Given my limited electronics knowledge, for ...
3 votes
3 answers
209 views

Voltage measured across transistor and transistor base current don't match calculated values

This is a newbie question regarding my second electrical circuit. I've built a switch on a breadboard using NPN transistor SS8050 and it works though voltage across transistor's collector and emitter ...
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2 answers
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What are junctions in a transistor and how does current flow in them?

I want to clarify what "junctions" are in an NPN transistor and how current flows in them. Is the area inside the blue circle considered the "BC" junction? According to wikipedia ...
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4 answers
339 views

Clarifying how a NPN transistor can act as a switch with a LED in a circuit

I'm experimenting with a simple transistor/LED circuit but after reading many articles online I still can't tell if I have a faulty transistor or things are working as expected. Power source = 5V DC ...
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2 votes
3 answers
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Can an NPN transistor have its base connected to the same power input as the collector?

All the tutorials I have seen on using an NPN transistor as a switch have base and collector attached to two different power inputs with two different resistors: My question is, can the base just be ...
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1 vote
1 answer
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High-voltage (48 V typ.) switching circuit

I am working on a design where the input (48 VDC) has to be supplied to I/O when a particular condition is met and the rest of the time it should be grounded. A relay is ideal for this, but the PCB ...
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3 answers
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What are the invisible reasons why many discrete transistors do not qualify for automotive use?

I looked today at the datasheets of this unqualified and this qualified product (per the AEC-Q101 automotive standard) and found no substantial difference, but I assume some stress damages only the ...
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NPN transistor small output voltage

I just learned about measuring the base resistor of a transistor but I think I did something wrong. I wired everything up like this, but when I measure it I only get around 2.7V out of my device. Is ...
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Time delay of LED dimmer circuit problem

I made a LED flip flop circuit using NPN transistor, it works pretty fine. But my problem now is I don't know how to control the on and off time delay for the LEDs using potentiometer. I tried putting ...
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How does T3 turn on?

This is a part of a well known product created by Markus Frejek and now maintained by Karl-Heinz Kübbeler (more info). It is the famous "transistor tester" or "component tester" (...
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Use of MOSFET or BJT

I'm trying to fix this water dispensing pump, and got stuck in between MOSFET vs transistor working principles. For some reason the MOSFET stopped working and the pump as well. Now I am trying to ...
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2 answers
238 views

My Tesla coil is not working

I made a Tesla coil, but it doesn't not work. I used this circuit: I used 200 turns for the primary coil with 0.5 mm wire and 5 turns for the secondary coil with 1 mm wire on a wooden rod. Back to ...
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3 answers
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How do I invert transistor output?

I have a transistor circuit as shown. There is a gate signal (in red). When the gate is HIGH (3.3 V), it is supposed to allow the signal to pass and the output should match the input. When the gate is ...
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Transistor parameter in Proteus

I am just learning the electronics and by the help of proteus I am learning the behaviors of different components. Could someone please tell me how do I change the Emitter current values of a ...
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IOREF default voltage reference circuit with two NPN transistors

I'm trying to build a small circuit to sense when a voltage ref (for IO output) is supplied otherwise set a default voltage reference. A bit of context - This is common within the Arduino ecosystem ...
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4 answers
115 views

An NPN transistor without its collector-base voltage [closed]

What would happen if I remove the base-collector voltage from an NPN transistor and put a wire connecting two ends of the voltage source? I believe that it it will work nicely. As the collector ...
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3 answers
128 views

P MOSFET without gate resistor. Why is this not burning up?

I have used this circuit several times and it appears to function as intended, but looking at it I am not sure why it doesn't fail. The intention was for MCU GPIO on the NPN transistor's base to make ...
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3 answers
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Voltage amplitude of Hartley oscillator

I am trying to follow these videos to learn about oscillator circuits; Hartley, Colpitts, and Clapp oscillators and they're all helpful to understand the LC relationship for frequency. I am concerned ...
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Self biased transistor current limiter

I am analysing the below self biased transistor circuit and have some questions: Why does the transistor in self biased arrangement never go into saturation for a light load? When the emitter ...
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Why do you put the load of a transistor on the collector side and not the emitter side? [duplicate]

Everything that I have read has said to put the load on the collector side and connect the emitter to ground directly, but I am having a hard time understanding why this is. Why do both PNP and NPN ...
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Weird NPN transistor symbol with a box connecting all three pins?

I've come across this symbol in the datasheet (link below) of a transistor for a halogen "electronic transformer" that uses two in a half-bridge operating at about 35KHz. The datasheet ...
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2 answers
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NPN high-edge flipflop [closed]

I'm looking for a design of an NPN flip-flop that reverses its output when the input is brought high. I'm looking to use the 2N2222 for this purpose.
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1 answer
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5V Input and Output interfacing with 3.3V GPIO [closed]

I have a device (a motor drive) with 5V logic. My controller is 3.3V. I draw the two circuits. The right sides are fixed in the device. I have some exact questions about calculations. -...
-1 votes
1 answer
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Shift register does not output voltage [closed]

I am building a 8x8x8 LED cubic matrix based on an Arduino. My schematic and PCB design was based on the one posted by Tapendra Mandal on Youtube. When I finally connected everything and try to write ...
1 vote
2 answers
61 views

Stopping reverse flow of current

The above circuit has two sections. Section A is a simple transistor as a switch circuit using BC547 NPN transistor which triggers a LED1 as well as section B. Section B is a NOT gate circuit using ...
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4 votes
2 answers
206 views

Increasing the forward voltage required of the PNP transistor?

I am a newbie and was reading about the uses of a 555 TIMER. I came across a project to create 40 LED Bicycle Light in Led Circuits. I can understand the diagram and most of the explanation except ...
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1 answer
125 views

NPN transistor to turn ON an ATTiny85 from a pinout of an ATTiny85

I have 2 ATTiny85 and a NPN CS-9011 used as a switch. They are both powered by the same 3.3V. I use pin 1 to run the base of the transistor with a 1K resistor. This is not working after an afternoon ...
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Advantages of using 2 NPN transistor NOT gate

Is there any benefit using 2 NPN transistors for a NOT gate rather than one NPN transistor?
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1 answer
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Increase the voltage in a simple NPN circuit [closed]

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,...
5 votes
3 answers
1k views

Transistor as a switch driven by a square wave

I'm trying to understand how to use a transistor as a switch. I'm sure I am not doing this right. The input signal is a simple 30 kHz square wave, 3.3 V amplitude. There is a second gate signal which ...
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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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Common emitter amplifier with low impedance

The following schematic shows a common emitter amplifier driving a resistive load. The common emitter has a high output impedance, is it possible to use the amplification achieved with the common ...
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2 votes
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Design of transistor amplifier for nanosecond signal (with NPN transistors)

For a project/learning experience I want to design/build an amplifier. The signal I’m provided has an approximately 1ns pulse width (duty cycle of 1%) with a peak of 2.2V and a repetition frequencyof ...
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2 votes
1 answer
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Why does my transistor explode in a simulator?

I'm new to electronics and I can't identify the reason why my transistor explodes when I simulate it. I am simulating a simple common emitter amplifier with a power supply of 12 volts.
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2 answers
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NPN Transistor amplifier - Base emitter amp

I would like to understand/create a circuit which amplifies an input signal with a base-emitter follower. Sadly, I’m not getting any amplified signal at the output. I don’t really understand why on ...
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3 votes
4 answers
891 views

What is the maximum voltage applied to NPN transistor base? (like for MMBT3904)

I cannot really find out what the maximum voltage one can apply to the base of the NPN transistor in a circuit like this one is. I highlighted the base in question. Can I apply more than the typical ...
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1 vote
2 answers
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Correct way to drive a 12 V motor from an Arduino with an NPN transistor

Looking for some help vetting my circuit design, it's been a long time from my college days messing with electrical stuff. My plan is to have an ATMEGA328 with the Arduino bootloader driving a 12 V ...
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1 answer
138 views

BJT NPN transistor

I am confused on a topic regarding NPN BJT transistors. When there is a collector-emitter voltage (VCE) applied to the NPN transistor (as shown in the figure) without a emitter-base voltage (VBE), it ...
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2 answers
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Switching the GND of a Wheatstone bridge using NPN

I am trying to turn on and off the power supply to this bridge by using a micro controller. Can I use the following switch using an NPN ? Edit: A switch using a MOSFET - a better option?
1 vote
3 answers
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What is the role of the diode in this heat sensor circuit?

simulate this circuit – Schematic created using CircuitLab I am building a heat sensor circuit using this circuit model. What I understand is that the \$\beta\$ parameter of the NPN transistor ...
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109 views

BJT type Gilbert cell does not work

I designed a Gilbert cell for analog multiplication, all the transistors (NPN) are in active region as I checked one by one, however, the result does not seem correct at all. How can I make it better? ...
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(Update)Using a bidirectional optocoupler for attaching any PNP & NPN sensor type [duplicate]

I have two different 12 V PNP & NPN proximity sensors. My first design was for each sensor type, having an identical PCB design with a normal optocoupler with a dedicated wiring arrangement. My ...
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What type of npn /diode is this?

I try to replace a sot 23 npn. The only markup is "NV" . It's used to switch a relay. I tested it with two transistor tester. Both of them show me a diode with the npn symbol. I dont know ...
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1 answer
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Why doesn't the current in a BJT transistor depend on the emitter-collector voltage?

In my understanding, in an NPN junction for example, an increase in the emitter-collector voltage should widen the depletion layer in the base-collector junction therefore increasing the electric ...
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1 answer
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Why do we need to connect the load before NPN transistor [duplicate]

I am trying to use transistor as switch and getting confused with the workings. For a NPN transistor, Collector needs to be connected to +ve and emmiter to -ve. If we look at the schematics below, in ...
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2 votes
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How to include the Early effect in NPN BJT current equation?

To understand the NPN current equation derivation, I have been studying my lecture handout and the emitter current equation accordingly is found as : \begin{equation} I_E= q n_i^2 A(\frac{D_p}{N_{dE}...
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How does class AB amplifier biasing work exactly? [duplicate]

Can somebody please explain in both cases the biasing method? I don't understand the following points: It's OK that we need ~0.7V for PNP and NPN base-emitter voltage, that's why a diode is used for ...
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