Questions tagged [base]
A BJT (bipolar transistor) has three leads: base, collector and emitter. In most cases base is used to control the transistor.
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How to keep a transistor's base current constant with varying input voltage?
The problem:
In the circuit displayed below, I have a microcontroller supplying current to the base of a NPN 2N2222 transistor. When the battery is at 9V, this setup works great: the microcontroller ...
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Voltage follower simulation low base current
I am trying to get a deeper understanding of how transistors actually work so I can design my own circuits around them.
Pictured is an LTspice simulation of a simple voltage follower circuit. I do not ...
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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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No resistor to limit base current in this BJT application?
A manual fan controller in my PC just 'sploded: fair enough, it was about 10 years old, and driving more fans than appropriate.
I got around to fix it, and figured I needed to change the BJT, because ...
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BJT small-signal base resistor voltage
simulate this circuit – Schematic created using CircuitLab
I am doing a small signal analysis of the following common-emitter BJT stage and I am trying to calculate the voltage across r_π (v_π). ...
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Physics of bipolar transistor turn-off
In a class AB follower push pull amplifier output stage* operated open loop and driven from a low impedance source, these are, from top to bottom, the emitter currents of both transistors, their ...
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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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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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Determine the Base Current Amplification factor using Ltspice
I'm trying to calculate the resistances of my circuit but I'm stuck because I'm missing the B value and don't know how to find it out .
I want to calculate the resistors with which I can determine the ...
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NPN circuit (breadboard)
What does this NPN BJT circuit represent, is it a switch or just a PN diode, and what should this plot look like when we sweep the value of Vbe, and why?
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NPN transistor switch wireless charger module
I am using this module for wireless charging, as a receiver, and i want to switch it on and off, because firstly it consumes about 5mA when idle and secondly i want to power it off when the battery is ...
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Problems finding voltage between two points (transistor)
I am having a homework question about transistors where I am asked to find the voltage drop between the base and the collector (Vbc). I drew the circuit in Proteus but I am not sure where to put the ...
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maximum collector-emitter voltage in BJTs
I am reading BC817 datasheet. According to the datasheet, maximum collector-emitter voltage at open base condition is 45 V. In typical applications we don't use open base configuration. My question is ...
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Confusion about NPN base connection
I found an over-current protection schematic, but I am confused about how the base of the Q3 is wired. Is it connected to a potentiometer? If so, to what terminal?
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Transistor for 5V relay
Following up this question I need a transistor to switch the necessary current through the coil. I have some spare BC817 lying. My digital output pins can switch 5V@20mA.
Do I need a base resistor to ...
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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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Why the base current is zero in B part of this question?
In the B part of this question , i am not getting why the base current is zero. Everything seems to be fine but still not getting ...
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Where to find details of dimensions and doping of a typical bjt
I have been searching for dimensions and doping levels of base, emitter and collector for a typical bipolar junction transistor presently in use. I have tried searching on internet and seen datasheets ...
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PNP Transistor with low base current
I designed a PCB with the following schematics.
simulate this circuit – Schematic created using CircuitLab
The circuit uses a MAX6369 external watchdog timer which has an open-drain output(...
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How to select a diode for a Baker clamp?
What are the requirements when selecting a diode for a Baker clamp circuit?
How does the reverse leakage current of the diode affect the circuit? Can a diode with relatively high reverse leakage ...
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Transistor base/collector voltage
I've read that with an NPN transistor, there is a voltage drop of about 0.6 V between the base and the emitter, so you need to have about 0.7 V on the base to switch it on (circuit 1).
But what ...
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Base resistor configurations, are there any differences?
Sorry for the noob question. From my understanding, R1s acts as pull down resistors for the base and R2 will limit the current flow to the base.
I have seen both configurations, but couldn't work out ...
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Circuit with Base of Transistor connected to ground
I am having troubles understanding a circuit where to base of a transistor is connected to the ground.
As far as I know a transistor needs a certain voltage on the base so electricity can flow from ...
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maximum emitter base reverse voltage limiting when driving with op amp?
This is part of a larger circuit, but problem area is shown below. In simulations (of the larger actual circuit not shown), the base voltage of Q1 drops to about -6.35V. Can this damage Q1 (2N3904)? ...
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Calculating base resistor value using voltage
I'm pretty new to electronics so my question is I think a relatively simple one.
On transistor datasheets, the base-emitter voltage is typically around 6V, which means that voltage across this ...
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Negative base current
I am designing a flyback driver using a salvaged power transistor that was originally the driver transistor of a flyback in a ctr screen.
This power transistor is the 2SC5681
I want to drive this ...
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I need to calculate the NPN bjt 2N4401 base resistor
I'm using the transistor (NPN bjt 2N4401) as a switch to light up 20 leds
(leds use 2v 20mA) (my power source is 6V).
How to calculate the base resistor?
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Is maximum BJT VEBO rating exceeded in this miller effect compensation circuit?
I have an switching circuit containing a transistor to switch the inductive load. There is a miller effect compensation capacitor (C1) in parallel with a base resistor. (The values of the two ...
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Mixing down to base band
What exactly is the base band? I always thought that it is a synonym to intermediate frequency but it appears not to be the case.
For example I have Bluetooth signals in the range of 2.4 to 2.48 GHz. ...
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NPN driving PNP, Diode from NPN Base to PNP Collector?
I am reviewing some old 12V alarm designs that use the circuit below to activate a siren. The design has been built on PCB and I have confirmed proper operation, proving the schematic is not flawed (...
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My teacher said a BJT phototransistor doesn't have a base
But I find it to be absolutely incorrect. How can a BJT transistor even work without a base? Shouldn't a transistor without base be just a semiconductor (PP, NN)? Does there exist some special NASA-...
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Doubt regarding Nyquist theorem for sampling analog signals [duplicate]
If for an arbitrary signal H(f) = 1 for 300-f-3700 Hz; 0 otherwise, what should be the minimum sampling rate? 7400 Hz or 6800 Hz and why?
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Base resistor on NPN transistor
I have recently started medelling in the understanding of circuitry and have started creating this project. As i bought the SSR from eBay i strongly suspect it is a fake and will probably not handle ...
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S8050 D331 base resistor calculation
I was trying a basic transistor circuit to understand transistors (LED on the collector without a base limiting resistor ).
Now on to the next step, to know where and when to put what values of ...
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"Reverse etch" PCB base(not the copper)
Is there a reliable way to etch a PCB(from working product) so as to be left with the surface without the substrate?
Sometimes an existing PCB product which wasn't designed with weight, size or ...
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Find the base potential
Question "a" says "find the base potential Vb", and I can't do it :(. All the resistors are given above (you don't need to understand french, don't worry)
Could someone help me please, I would ...
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BJT gain.Width of base region vs collector current
We know that in active region Ic=beta(Ib),so it means that as Ib decreases the Ic should decrease proportionally,but the early effect states that as we increase Vce the width of the base region ...
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What is happening with resistors in series/parallel at the base of a BJT?
(source: subefotos.com)
R1 receives 5 volts from the Arduino, but with a low current. The BJT is used to amplify the current. Every example I have seen of this does not have the R2 in that way. What ...
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Calculating base current
The task is to find the operating point of this transistor: Given information:
\$E_{C}=12V\$, \$V_{BE}=0.6V\$, \$V_{IN}=5V\$, \$\beta=200\$, \$R_{B}=440k\Omega\$, \$R_{C}=5k\Omega\$, \$R_{E}=3....
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Why am I getting negative base current in LTSpice simulation?
When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in ...
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NPN Transistor; base grounding through emitter
I am using NPN transistors in an H-bridge to connect a DC motor to ground. My problem is the base of the transistor seems to be grounding through the emitter pulling the value of my logic circuit to ...
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NPN transistor negative base voltage
In this circuit, when I switch off the transistor opening the switch SW1, a negative Voltage of circa -6.5V appears at its base.
I would like to understand why, my first hypotesis is because of the ...
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investigate the influence of the collector current on the base current in an n-p-n transistor
simulate this circuit – Schematic created using CircuitLab
why does the base current decreases as the collector current increases?
And as the base current increases the collector current also ...
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Effect of negative voltage at NPN transistor base (interesting example)
I'm trying to understand the behaviour of an NPN transistor and two diodes connected to the output of an instrumentation amplifier [image below]. The transistor appears to switch on when there is a ...
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BJT Circuit Base-Emmitter voltage
I don't understand, why the voltage V2 is approximately Vb.
Can't V2 be 0, if Vb is enough high, so that the emmiter-current of Q2 is Ie2?
The assistent only told me, that because both transistors ...
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Simple Circuit Analysis, why this cap is needed?
This is a sub-circuit that is part of larger design and I was wondering why the designer choose to use C1 inline with the BJT base? and what does the combination of R1, C1,R2,R3 do?
Since the max ...
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Fundamental questions about BJT transistors
Take a standard NPN transistor. The doping of each element of the transistor is in the name. This is what is inside the transistor...
Source of image: Bipolarer - Transistor, gif
The left "slice" of ...
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Synchronous motor base speed calculation
I would like to ask the following question.
How can I calculate the base speed of a Synchronous motor for variable speed applications controlled in dq frame?
I want to calculate the base speed for ...
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unexplained short circuit with PWM signal?
Something happened that i haven’t been able to explain , I wrote a program to output a PWM signal, this to activate a transistors base using a PWM which I could change the frequency using a ...
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Transistor Emitting Without Collector [closed]
I'm pretty new to the hardware side of electronics and am building some basic logic gates. The first Im trying is an AND gate and the problem I'm having is that whenever I power the base of the ...
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