The transistor is a semiconductor device that can amplify signals and switch power. Most used types are bipolar (BJT, for Bipolar Junction Transistor) and MOSFET (FET, for Field Effect Transistor)

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Beaglebone black + serial enabled LCD

I'm trying to interface a SparkFun Serial Enabled 16x2 LCD (3.3V) to a Beaglebone Black. Since the beagleboard has on-board 3.3v and ground, I used that for the power to the LCD. For the 3.3v TTL ...
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60 views

Matched biased transistor circuit

Hi, I've a question, what is the role of the capacitor C in this circuit? What should be capacity of this element, and how can i find/calculate the voltage gain of this circuit ? Thanks for reply ...
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57 views

Reusing a old non perfectly regulated 12v powersupply

12 volt power supply shows 16.8 volt Not long time ago i made a simple low voltage rgb pwm circuit to test with raspberry and arduino. Now after a while of reusing old chagers and recycled ...
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60 views

NPN Transistors [duplicate]

How does NPN transistors actually work? In the picture below, I understand that electrons flow in A as the n-p junction of the Emitter and Base is forward-biased. However, the p-n junction of Base and ...
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216 views

What's the usage of these coupled transistors?

I'm thinking to know What is the usage of these parts of this circuit. Source It's the schematic of UT70C Digital multimeter.
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219 views

What to choose hFE or beta from the plot of transistor's datasheet

Suppose I have this BC635 transistor, if I look at hFE then I'd say that the lowest value is 25 from that table in the ...
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3answers
85 views

How to choose transistor for switching bigger MOSFET

Leading on from my last question: MOSFET choice for 12v LED Strip and 3.3v Logic I have decided to use the IRFZ44N (despite it not being ideal for the job) for being economical the cheapest option and ...
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2answers
44 views

Basic 12V Step-Start Circuit For Automotive Fans: Troubleshooting

To keep this short and sweet, I wanted to make a circuit/controller to decrease the inrush current on a large powerful fan for my race car. I ideally just wanted something that wouldn't let the amps ...
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3answers
73 views

Basic power: drive 12v LED from 5v Raspberry Pi output — no 12v supply available

There are a lot of questions on here and elsewhere about this. The consensus seems to be to use a transistor to switch a power supply — implying that I have a 12v supply available. Only 5V is ...
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1answer
46 views

How to find Vce SAT in NPN transistor datasheet

I am trying to find out the VCE value when the collector current is 150 mA (Controlled by the load). the base current is 4 mA. What is the VCESAT value when the base current is 4 mA? part: BC817-40 ...
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52 views

pmos transistor acting as pull down device

I have a simple question related to the pmos transistors. Why can't it be used to fully pull down a high voltage signal? Can somebody please help me to understand the electrical characteristics behind ...
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2answers
53 views

Transistor not supply enough current

I am trying to run a 100W 32V Led with a DC-DC boost converter from a 6 volt battery, and I want to make it so it will shut off when the battery voltage gets low. So I am using a TIP122 transistor ...
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1answer
41 views

How do i turn multiple usb ports off based on multiple sensors

I'm looking for a way to turn a usb port on an off from an Arduino, I'm looking at purchasing something like this and somehow using a pressure or light sensor to turn the usb port on and off. I was ...
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1answer
130 views

Why use a transistor for getting a Constant Current Source in a circuit with an op amp?

I have used the above simple circuit for a constant source where \$V_{\text{in}} = -5\$V, \$R_{\text{in}} = 390\Omega\$, \$R_f\$ is the load which ranges from \$110\$ to \$170\Omega\$....would using ...
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1answer
29 views

Microcontroller output does not change when connector to MMBT2369

I am trying to Optoisolate a signal from microcontroller. I am driving the signal to base of MMBT2369, and opto isolator LED is connected to Collector of the transistor. When transistor is not in ...
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2answers
142 views

SMD vs THR Transistor for Relay

Designing a Relay control from a MCU's GPIO, there are some requirements to take into account. Coil Voltage: 3V Coil Resistance: [36-45]Ohm Relay Voltage: 250Vac // 30Vcc GPIO Voltage: 3V3 Max GPIO ...
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4answers
453 views

What is the total resistance of a LED array?

First time poster and a hobby EE enthusiast here. I want to turn on a LED array with a transistor switch and I'm having trouble with determining what will the total resistance on my transistor ...
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2answers
61 views

Need simple audio amplifier

I'm more of a programmer then a circuit designer (read: I'm not good with EE stuffs at all) but I'm working on an arduino project and it's not loud enough. I was trying to drive a piezo buzzer to make ...
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1answer
38 views

2n3906 Trigger is HIGH with no negative voltage

I'm trying to read the negative pulse coming from my motorbike coil. I'm using a 2N3906 to switch it from negative to positive so my arduino can read the signal, but when I put my prob on the trigger ...
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104 views

What is causing my arduino controlled fan to run so poorly?

simulate this circuit – Schematic created using CircuitLab Some background first... I am a mechanical engineer who took 1 electrical engineering class back when I was in college, but ...
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1answer
73 views

Led driver circuit 3.3v & 5v

Not long time ago, as i couldn't find a proper Mosfet to drive a high wattage led strip ( 5050,5630), i asked how to create a circuit that allows me to turn on properly the mosfets i already own. ...
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1answer
48 views

How Are Transistors Used to Represent Logic Gates [closed]

How are transistors arranged to form Logic Gates. Use an AND gate as an example
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Modelling a BJT with easy equations, but having false scenarios - II

I've revised a few things from this post here. Tweaked it. Redefined it (for clarity). Even provided the diagram for direct NPN analogue ("analogue", for comparison, not "analog"): simulate ...
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2answers
47 views

Depletion P-channel JFET that's saturated at \$V_{GS}=0V\$

Is there any depletion-mode P-channel JFET that is saturated at \$V_{GS} = 0V\$?
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1answer
73 views

PNP or NPN Transistor for this schematic?

I am quite new to electronics and hoping to build a voltage regulator using the schematic below. I will be using a 7806 regulator and a 7.4 Lipo battery (yes, the schematic is probably a little ...
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1answer
48 views

Easiest way to connect two pins when an output is off?

I'm planning to build a switch that turns off the power supply to my Raspberry Pi when an integrated circuit (ATtiny 85) output pin is low. The power supply (Adafruit PowerBoost 1000C) goes off when ...
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2answers
436 views

9V wallwart powering a fan via Raspberry Pi

I have a fan rated at 12V, 0.14A, 12/0.14 = 85 Ohms (taken from an old PC case) and a wallwart that outputs 9V, 1A. I have ...
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3answers
159 views

Thevenin equivalent in a nonlinear circuit

Is it possible to use the Thevenin equivalent of a voltage divider driving an emitter follower? simulate this circuit – Schematic created using CircuitLab In general, when is it safe to ...
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55 views

Modelling a BJT with easy equations, but having false scenarios

NPN: simulate this circuit – Schematic created using CircuitLab ...
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2answers
83 views

Trouble with Transistor Switch (2n3906)

simulate this circuit – Schematic created using CircuitLab I'm replicating a circuit found on evilmadscientist.com: the "detecting darkness" ...
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1answer
51 views

power transistors use in electric car

the battery rating is 48v and the motor in electric car rating is 3.28kW.h/100km. i will connect a power transistors with a microcontroller(output from micro controller only 5v) and also the motor. ...
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1answer
44 views

Clarification on region of operation in MOSFETs

So this is going to be a series of questions: Enhancement MOSFETs: N-Channel: So applying positive voltage and up to the gate, relative to source, lets more and more current through until it ...
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2answers
125 views

How a transistor works?

I know this question is asked a lot and answered well in many posts, however, I'm still confused. A switch transistor works by using a semiconductor to pass the current from an emitter to a ...
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2answers
47 views

Unsure of transistor to use for LED strip

I'm trying to control an LED strip by means of a Raspberry Pi, replicating what is done here: http://popoklopsi.github.io/RaspberryPi-LedStrip/#/ It recommends using the IRLZ34N transistor between ...
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1answer
47 views

Can I use a NPN Transistor as a Varactor Diode?

I am currently building a crystal controlled AM transmitter. The circuit that I'm using call for a NTE – 613 varactor diode (which will come in a few days). I was wondering if there was an alternative ...
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2answers
253 views

How do floating gate transistors not leak the stored charge?

I've done my best to read through Wikipedia explanations of floating gate transistors which are used in flash memory. It looks like these transistors have a special region where the charge is "stored" ...
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1answer
71 views

Are transistors interchangeable?

I do know the question in the title is really stupid, but it is the best phrasing I could come up with. Let's say I am building a circuit and the schematic says to use a BD139 transistor. Would ...
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1answer
495 views

How does this BJT transistor circuit works?

I just wanted to know a little more about this circuit about how it works a more in depth analysis I mean. I know there's some kind of differential amplifier and a Zener diode for voltage regulation ...
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1answer
52 views

How does an electronic shocker works?

I'm new to electronics but I want to make this diagram from "Instructables" : I have everything I need from a camera... I also realized, using a different transformer, that the sparks are made only ...
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1answer
60 views

Newbie problem with transistor switching

First post, so I hope that I adhere well to all the rules. I couldn't find any other posts that could help me, so here's my problem: I am trying to build a simple transistor switch with a 3906 PNP ...
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1answer
52 views

How to calculate input and output impedance of BJT Common-Emitter amplifier circuit

Why is the input impedance not 260Ω in this circuit? I calculated this impedance as follows: \begin{align*} I_B &= \dfrac{18.7V - 0.7V} {180kΩ} = 0.1mA \\[1 em] r_{\pi} &= ...
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1answer
341 views

What is the purpose of transistor in this circuit?

"A zener diode voltage regulator is inefficient when the supply is used with equipment that draws high current. When a supply must deliver a lot of current, a power transistor is used along with the ...
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2answers
88 views

NPN transistor: collector current flowing to emitter without connecting base?

I have a circuit where a LED has its cathode connected to the collector of my C8050 (or SS8050) NPN transistor, with the emitter grounded. Even though the base is left floating, the current is still ...
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1answer
48 views

Explaination of high current zener transistor regulator circuit

This is a high current zener TRANSISTOR regulator circuit. I want to know What does "high current" mean here? How is this circuit working as a zener regulator? What is the purpose of transistor ...
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3answers
130 views

Why does a BJT act as an amplifier in the linear region?

I'm covering BJT's in my semiconductor class and in lecture, the professor said that BJTs are used as amplifiers in the linear region. I'm confused because I thought the gain was proportional to the ...
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3answers
95 views

Why signal is inverted in common emitter amplifier?

Why signal is inverted in a common emitter amplifier?
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3answers
287 views

How to choose components for a circuit

I designed a simple circuit: that I would like to put components on - the point of the circuit is to light the LED when the voltage source is above 4 volts (it won't be more than 5), so I am ...
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37 views

Reverse saturation current in a BJT: active and reverse active modes

In (Sedra; Smith. Microelectronic Circuits), as well as in several other sources, the value of the reverse saturation current (\$I_S\$) is considered the same for the active mode and for the reverse ...
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1answer
82 views

ULN2803A PWM LED High Watt/Ampere

Reading the ULN2803A datasheet, especially the part "Figure 13. ULN2803A as Inductive Load Driver" and after various fails to properly drive 12v RGB led strips, as i can't find the proper mosfets. i ...
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4answers
943 views

Why are NPN Darlington transistors used to sink current?

I notice that NPN Darlington transistors are commonly used to sink current. Wouldn't it make more sense to use PNP for the purpose? This would avoid shunting the load current through both junctions at ...