Questions tagged [transistors]

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

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Is this single transistor interface good enough for this relay-control?

I need to turn ON/OFF an 12V 10A SMPS supply by a relay. I want to switch the SMPS via its line input using a microcontroller. I need a normally open non-latching magnetic relay such that the SMPS ...
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PNP TIP126 transistor hot to touch while in use

I have a 7-segment mechanical 'vane' display andbgot it working using a circuit originally suggested to me here. The diagram below is a slightly modified version. Each vane draws around 0.2A of ...
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Automatic dark detector: base voltage

Here we have the typical “automatic dark detector” circuit: Let’s assume LDR=5Kohm with light, and LDR=2Mohm in darkness, the battery is 12V instead of 9V, and the transistor has a forward voltage ...
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-3 votes
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Help needed in project [closed]

Greetings fellow electrical engineers, it is requested to explain how to design this circuit. Can it be done via MOSFET or should it be done without a MOSFET? If it can be done with a MOSFET, how?
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Resistive Moisture Sensors, What is the purpose of the 2N3904 Transistor in the Sparkfun Circuit?

the two circuits below do the same things as far as I can tell, they both measure soil moisture using resistive sensing. However the one from Sparkfun is using a 2N3904 transistor, since the voltage ...
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-1 votes
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Clap sensor Proteus simulation issue

I've been trying to connect an electret microphone into this circuit, although none of the imported electret microphones work. The circuit is designed to keep the LED open for about 1 second by the ...
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3 votes
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GaN Vs IGBT performances

I was making some research on GaN and I do not understand why GaN is so reveolutionnary. When I take a look on the following specification RdsOn and Coss (Cds + Cgd), the GaN semiconductor has lower ...
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Maximum current going through a solenoid

L1 and R3 represent a solenoid in the schematic below. In my textbook, it's mentioned that the maximum current through the solenoid can be approximated as the voltage supply (Vcc) divided by the value ...
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Thevenin's theorem for Voltage divider bias

I am calculating the base current of transistor Q1. To simplify the circuit equations, I applied the Thevenin's theorem and converter V1 and R1, R2 into Vth and Rth as shown in the image. Vth= V1x(R2/...
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2 answers
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Control 12V relay by using Arduino [closed]

I have an Arduino Mega, 12V relay module, and 12V external power supply. I want to control relay state (on/off) by using Arduino I/O pins (5V). Is it good idea to use following simple diagram? There ...
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Base resistor too low problematic?

I have recently designed and ordered some PCBs which can combine a horizontal and a vertical video sync signal into one composite sync signal (all are TTL signals). This is done using a BJT circuit ...
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4 votes
2 answers
253 views

Designing a common emitter audio pre-amplifier

I am trying to design and simulate a common emitter audio pre-amplifier using 2N2219 with characteristics based on industry standards (audio frequency response, etc. Corner frequency must be less than ...
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-6 votes
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What are those components for? [closed]

So I have three different circuits and I need to purpose of some components in them Series resonant converter circuit. What is the purpose of Lr and Cr components ? Variable speed/light control of ...
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Purpose of components [closed]

These schemes are not related to each other. Can someone tell me the purpose of the Lr Cr components here? What is the purpose of the 39 ohm resistor and 0.01uF capacitor? What is this circuit used ...
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Transistor Switch Output Current Increasing

I'm using a BJT switch to send a 48 V, 2.5 mA signal (thanks for all the help in the past!). I've been tuning the resistance value I need to output 2.5 mA and noticed that the output current is ...
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An over- and under-voltage protection system

How can the block diagram below operate as an over and under voltage protection system? I thought it will work as follows: A step-down transformer is used to bring down the alternating current supply ...
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Modifying RC controller to drive with Arduino [closed]

Good day all! I am trying to modify an RC car controller to control via an Arduino. The purpose is to send output data from a neural network running on my laptop. It's an autonomous RC car inspired by ...
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Weird thing happening with my latch circuit [closed]

I was experimenting with this basic latch circuit where you have an NPN transistor opening the base of PNP transistor to GND, and once the PNP is on, the collector latches into the base of the NPN, so ...
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Full wave active rectification for lower voltages?

I have been following these youtube tutorials on active rectification to learn more about the topic. https://www.youtube.com/watch?v=VR456CsHYx4 https://www.youtube.com/watch?v=arvNukW-jeo I simulated ...
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Can SOT-223 chips or any DC type of transistors receive 12 V from a 19 Ah lead-acid car battery? [closed]

Can SOT-223 chips or any type of DC transistors receive 12 V from a 19 Ah lead-acid car battery? Will the 19 Ah current kill the DC transistors? For example, using an AMS1117 to produce 3.3 V. The ...
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1 vote
1 answer
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Graphing modes of BJT

Suppose we have this Ic vs Vce graph of a BJT transistor I have been taught this graph is applicable for this BJT transistor configuration. simulate this circuit – Schematic created using ...
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Can IGBT close during surge current?

IGBTs can withstand transient current for a limited time, e.g. This IGBT is rated 140A, but can withstand 1200A for less than 1ms. My question is can I turn off IGBT during that 1ms ? of course there ...
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Driving an RGB LED Strip with an ESP8266

simulate this circuit – Schematic created using CircuitLab That's my circuit, although it's an RGB LED strip that I'm driving, rather than three individual LEDs. It works. I can PWM each channel ...
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IR remote code amplifier

I am interested in amplifying output mod signal of my tv remote in order to use a higher power led/vcsel. Now, it should be as simple as cutting the emitter led and putting a transistor that would ...
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1 answer
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The source part of an IRF540N transistor

So, I have built a DC-DC booster using an IRF540N as my transistor, according to the following schematic diagram. It did work and I had a 18V output from a 1.5V battery. The transistor is connected ...
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4 votes
2 answers
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How to stop current from passing through a transistor?

I have this circuit. When sw1 is open the LED should be off. The thing is, some current passes through the transistor even though it's off making the LED light up dimly. Is there a way to fix this, ...
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1 answer
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How to determine type of a BJT by using an ohmmeter?

Our lecturer in Analog Electronic class mentioned about determining the type of a BJT (whether it is PNP or NPN) by an ohmmeter. I know that in some applications we can determine the type by the ...
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2 votes
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DC-DC booster functionality

I am working on a DC-DC booster. I have already built it, boosting 1.7 V to almost 18 V. I am using an IRF540N as my transistor, an inductor, a diode, and two capacitors. I was reading about how the ...
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1 vote
2 answers
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Is my circuit analysis correct?

This is the circuit. It is assumed that beta is 99 and VBE=0.7 V for both transistors. Here is what I've done. Multisim confirms the first set of values I worked out regarding Q1. However it does ...
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4 votes
3 answers
256 views

Why is this transistor in my bootstrap driver failing?

I'm trying to implement a bootstrap switch circuit for an N-channel high side switch. I implemented the following circuit on a breadboard: Testing it with a 24V power supply and a grounded input ...
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-1 votes
1 answer
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Why is current flowing through the transistor though the base is off?

What could be wrong in this circuit? I'm new so I'm still figuring it out. I assume it's because I don't have a resistor placed at the emitter. I did that on purpose because I'm just testing it out. ...
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1 answer
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JFET source follower input impedance without gate resistor

I am trying to do a high bandwith and high imput impedance analog front end for a mini oscilloscope project. I am using a JFET for this purpose. I accounter a weird behaviour and i don't understand it....
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1 answer
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I don't get the formula RIN = beta * RE

There is a formula in Malvino's book (page 210 of the 6th edition) which states that the input base resistance of a transistor is beta times the emitter resistance. To quote: "When seen from the ...
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1 vote
1 answer
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Looking for advice on a 12V relay circuit with ESP32

I've made the below circuit on a custom PCB and it doesn't appear to work as intended. For whatever reason, I'm seeing only ~3.8-4V on the coil pins of the relay rather than the expected 12V needed to ...
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2 votes
1 answer
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How do I identify this power transistor? Markings 042R5NT EW1A5NA

I took this transistor out from an DC to AC pure sine wave inverter and tried to Google the markings written on it: 042R5NT, EW1A5NA; but couldn't find anything. I suspect that it is a power MOSFET ...
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Does anyone know why this diff amp isn't working?

simulate this circuit – Schematic created using CircuitLab I'm new to electronics and I've been figuring out how a diff amp works. I followed a schematic I found on YouTube. Basically, as V3 ...
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0 votes
1 answer
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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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Which type of MOSFET is required to supply enough current to activate the coils?

I am using a NPN-PNP Transistor couple to act as a switch for activating the desired coil of my relay. If the H/L pin is in HIGH state, COIL1 must be supplied with 3.3V and if LOW, COIL2 must be ...
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2 votes
3 answers
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Are emitter and collector of a transistor fixed, or can I use either pin as either emitter or collector? [duplicate]

The question pretty much sums up everything.
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2 answers
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Firing a solenoid with a timer only ONE SHOT rising edge trigger

I have a button connected to 12V and want to fire a solenoid 24V ONCE every push of the button. No matter if the button is pushed 1 sec or one minute. The solenoid should fire more or less 1 sec and ...
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2 votes
1 answer
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I'm not sure my circuit analysis is correct

I'm an electrical engineering student. I analyzed a circuit, however I'm not sure I analyzed it correctly. This is the circuit. I'm asked to find the voltage drop between the bases of QN and QP. Base ...
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1 vote
1 answer
195 views

Transistored pre-amplifier

We have a transistorized preamplifier, which has a sinusoidal signal source as input. vi = VI sin(ωt). Being VCC >> VBE, VBE = 0,8V and the capacitors have infinite capacitancy. How can I ...
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2 votes
3 answers
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Calculating a simple transistor circuit

I have this circuit in the picture, and I am hoping to figure out the calculations/formulas behind it. It is a PNP transistor, is it possible to find out what the 'β' or the DC gain H(FE)? (EDIT: I ...
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1 vote
1 answer
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I can't figure out what this circuit does

I'm an electrical engineering student. The picture below shows a circuit that I found in some old notes but I cannot figure it out. I have been at it for the last 2 days but to no avail. Some things ...
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0 votes
1 answer
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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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9 votes
3 answers
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Triggering generic transistors with UV or green light?

Flashes of UV light can create electron-hole pairs in transistors. Or at least reports of the "UV flash bug" claim this happens in microprocessors. People observed raspberry pies reset when ...
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Why does MOSFET N back to back switch work?

Please consider an exemplary back-to-back MOSFET N driver IC (drew the body diodes of M1 and M2 for clarity): I understand how is it possible to turn off the M1/M2 transistors from the gate voltage ...
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5 votes
3 answers
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BJT: definition of "edge of saturation"

The book Sedra/Smith (Microelectronic circuits) tells in chapter 5 the following: My question: I found no statement on why the EOS is defined by the point where vc < (vb - 0.4V). Seems like other ...
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1 answer
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Which part of this transistor model op amp represents pin 5?

In this op amp oscillator pin 5 is connected to an RC circuit: I have a transistor model of that op amp and I want to connect an RC circuit to it like the above circuit: Since pin 4 and 8 represents ...
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Why in this circuit the collector of Q2 is receiving negative voltage?

According to when we say the collector in a transistor is reverse bias and the base and emitter are forward bias, why in this circuit (since Q3 or Q4 are NPN, so the emitter should be connected to ...
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