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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45 views

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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79 views

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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84 views

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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28 views

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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64 views

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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71 views

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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85 views

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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925 views

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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86 views

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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91 views

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 ...
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Large signal model analysis of npn BJT

I have the following circuit and I am trying to find VB, VE, and VC, and consequently IB & IC. The "hints" I am given are (1) to assume that vs has a DC value of 0V, (2) to use the large-...
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80 views

What is the point of the diode in parallel to the fan here?

Sorry - no background in EE so this might be a bit of stupid question. I'm looking at this simple circuit and am trying to understand the point of the 14N007 diode that is put in parallel to the fan ...
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42 views

How to control transistor with lower base voltage than supply voltage

Here is the link to simulation of h bridge that I built Simulation link in this I was somehow able to control transistors with 5 volts when supply was 9 volts but I still didn't completely understand ...
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4answers
164 views

Unclear about fluctuating frequency when using NPN transistor

I am trying to build a more complex circuit but am having trouble starting off. I am using tone() to generate a frequency on my 5V Arduino Nano on D3. If I measure the frequency directly at D3 to GND, ...
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70 views

What are the resistor values that I should use in order to get 38dB gain? [closed]

I have build a common emitter-common collector multistage BJT amplifier. I want to get an output gain of 38 dB under the conditions of 8 ohms load resistance, 6 volts, 25 mVpp input voltage signal. ...
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618 views

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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247 views

Activate 12 V Relay with a 5 V GPIO

What is the reason of using 10 kΩ resistor in series to the control signal? Is it related to the base current according to the NPN transistor's datasheet? For example: My CONTROL/GPIO is 5 V. The ...
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154 views

Confusion about when to use B*Ib = Ic vs the voltage diode equation for transistors to obtain Ic

When we have an NPN transistor in forward active mode, why do we sometimes use this equation to find the collector current I_c (whereby V_be would be the voltage across the base emitter junction)? ...
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1answer
75 views

How can I increase the base-emitter voltage of an NPN transistor in forward active region?

For a project which involves amplification, I think I have to increase the base voltage, keeping the emitter voltage the same so that my circuit will not go out of forward active region as the ...
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63 views

NPN transistor switch with load at emitter pin

I found a schematic with a 55 timer driving two transistors, each of which switches an LED (see below). When the 555 output is low, LED1 is OFF and LED2 is ON. When the 555 output is high, LED1 is ON ...
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149 views

How to convert NPN transistor to PNP transistor? [duplicate]

I am making a circuit using a 4 pin hall sensor with arduino. It turns out that the hall sensor outputs a negative voltage as output, which arduino cannot read, so I will need a PNP transistor, I don'...
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What happens when input current in common base amplifier circuit is increased?

Looking at the equations of the common base amplifier circuit shown below: The input current 𝐼𝑒 should be given by the equation: $$I_e = (V_{in} - 0.7)/R_e$$ Then, the output current 𝐼𝑐 should be:...
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73 views

Why does this transistor limit the current so much?

I have been trying to understand how a transistor works. I bought a simulator to be able to understand it better. Below is a small circuit I designed. The load is a lamp. The characteristics of the ...
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1answer
56 views

How do i control a 6 V supply output based on a 5 V input?

I have a signal from a microcontroller that varies from 0 V to 5 V. I also have a separate 6 V supply to power a motor. I'm trying to design a circuit that allows the microcontroller signal to ...
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2answers
269 views

Two BJTs together

simulate this circuit – Schematic created using CircuitLab So the BJT's B-E diode is turned on with 0.7V, and beta in active mode is 100 and beta in saturation mode is 10. I'm trying to find ...
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102 views

Water detector with a BC547 and help understanding transistors

I have set up a basic water detection sensor using a BC547 transistor to switch on an LED if there is current between two electrodes (which are spaced about 1 cm apart): I'm trying to understand more ...
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2answers
67 views

Transistor turns off only after a delay

I'm building an IC programmer (for the AS5043 sensor) that requires two voltage levels; 5V and 7.5V. I decided to control those with two PNP transistors. I'm controlling them from a 5V microcontroller....
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69 views

How to design a square wave inverter circuit without an op amp

I am using an NE555 timer circuit to generate a 0 to 12 volt 10kHz square wave. I would like to invert that square wave (so inverted signal is 0 when original is 12V and 12V when the original is 0 V.) ...
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68 views

Common base question

I'm trying to solve this problem where I find Vout/Vin if rπ if infinite. I also have to conside early effect. When I try to solve it, I get Vπ = 0 and that makes gm zero, a bit confused on that.
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How to choose the correct transistor?

I am having trouble understanding the definitions for the transistor. I am checking many different transistors and unfortunately every company has different words/symbols. For example, in one company'...
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74 views

2N2222 NPN Transistor, no current flowing through collector

I have a 2N2222 NPN Transistor wired up in the most basic common emitter setting (emitter grounded, base hooked up with a 1k resistor to 5V, collector connected to load and load connected to +12V). ...
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188 views

NPN Transistor Data Sheet, Source vs. Sink Current

Even though I'm an EE with 30+ years experience, a simple question asked by a junior colleague really stumped me. Namely, on a data sheet (e.g., for a 2N2222), that transistor can only SINK ...
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86 views

Question about diode connected transistor (BJT) with current source

I'm trying to find ΔV for this circuit, but I'm having a bit of trouble doing so. I think the current on the right BJT will be n times greater than the left, but I'm not sure about that either. It ...
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96 views

NPN transistor turning on with grounded base

The NPN transistor in bottom left with grounded base is turning on in circuit simulator for some reason. Can someone tell me why is this happening? Circuit Simulation link I know why the other 3 ...
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1answer
48 views

H bridge with a single I/O control and NPN at the top

I want to control a 4V motor to rotate both directions which draws 100mA and I was looking at the H-bridge schematics. The tutorial says that you should place NPN transistors at the bottom if you need ...
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32 views

Fast voltage regulator for output of an function generator

First, I am not an expert in the electrical field:) In a real-time control system (in LabVIEW), for actuating a piezoelectric, I use the generated signal (sine signal 20khz and 10<V<100 Vpp) ...
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57 views

Calculate base current NPN high side transistor

Say I have this configuration: simulate this circuit – Schematic created using CircuitLab I want to calculate the current going to the base of the NPN transistor. Specifically for PMBT3904,215 ...
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1answer
68 views

Why must the p type be connected to the power source, and the n type be connected to ground? [closed]

When we have mosfet transistors, why must the p-type be connected to the power source, and the n -type be connected to ground? I don't see what will go wrong if we do it the other way. But a book I am ...
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What is the (typical) value of SPICE parameter ISS for a (vertical) npn transistor?

SPICE gives a default value for the (collector) substrate leakage saturation current ISS. The default is ISS=0 but I would like to know the real value for an integrated vertical npn transistor. The ...
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211 views

Where did the base get the current from?

Still learning on my own so I am really not an expert. I built a small circuit and can’t get the expected behavior. Here is the schematic: This is pretty simple. The PNP on top is connected to 5V on ...
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38 views

Negative differential resistance on current sink

Let's assume we have this circuit: simulate this circuit – Schematic created using CircuitLab I was looking in creating a costant current sink but I have found something very interesting. ...
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39 views

Interpreting the state of the transistor

In this scenario, let's say that XMM2 has a reading of 0 A and XMM3, being a voltmeter, has a reading of ten volts. I presume that XMM2 reads the base current, so since there is no IB, there will also ...
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71 views

Using an NPN transistor as a signal switch

I'm using this NPN switch to turn on and off a clean guitar signal (as part of a much bigger circuit not seen.) The base is connected to the switch, which gives the base 9V through a 1 megaohm ...
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129 views

Transistor how to turn lamp on/off

I am trying to design a very simple schematic and trying to understand how the transistor works as switch. Transistor: Datasheet Description: NPN - Pre-Biased 100mA 50V 100mW USM(SC-70-3) ...
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229 views

Shorting NPN transistor base to ground

What is the normal convention(safe and reliable), should one connect NPN transistor base to ground or should a resistor be used? My logic tells me that in common emitter mode, shorting base to ground ...
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175 views

When using an open-drain output to drive an NPN transistor, can the base resistor be replaced by a pull-up?

Assuming the value of R1 is the correct value for the base resistor for the given motor L1, is it okay to omit the additional base resistor, used in push-pull applications, for an open-collector ...
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71 views

switching shape memory valves with microcontroller using NPN transistors

I am using a standard NPN transistor-as-a-switch set-up to use a Teensy 4.0 to switch a bunch of shape memory valves (valves controlled by a wire that changes shape when heated by a current). I have ...

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