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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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55 views

Inverting input of 555 timer

The common 555 timer triggers the output when the trigger signal falls down. Although this is not a problem, I want it to do the opposite, which is to trigger when the signal that controls the 555 ...
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1answer
34 views

Why the Base of T2 gets no more voltage if S1 is opened?

When S1 is closed, T2 no longer gets enough voltage to switch. Obviously it is because the capacitor is being discharged when S1 is opened, but what actually happens at the base of T2 when S1 is ...
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28 views

TO-72 package FET Case pin

I have 2N3823 JFETs in TO-72 package, which has 4 leads. No problems with Gate, Drain, and Source, but there is also a Case pin that I have been ignoring. Now I am putting together a PCB for a ...
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1answer
59 views

What's the actual difference between voltage gain, current gain and power gain?

Why do we intend to obtain different gains at different places? In an emitter follower for example, There's no voltage gain, but there's current gain and therefore it has power gain. Okay, how's ...
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2answers
104 views

Control 12V DC via MOSFET and normal transistor

I made this schema and I want to ask, how transistor control MOSFET. What that s8050 transistor do with the IRFZ44N MOSFET. Please, help.
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0answers
45 views

T Model of a transistor

I want to redraw this circuit based om the T model. Is this T model representation correct? Where Zth is the parallel between R1 and R2 in series with C1, re = (Vt/Ie) Vt being the early voltage, Z2 ...
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1answer
178 views

Can anyone explain the point of this dual PNP/NPN set?

I like to consider myself fairly experienced in Electronics Design, but upon being contracted to review this schematic I'm a little stumped. This is basically the output stage of a boost power supply: ...
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1answer
31 views

Common base bias divider resistances

I have been trying to grok the common base amplifier, and put together a few examples, but there is something that I do not get at all. I have the setup below. Things are working more or less as ...
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1answer
59 views

Will I be able to keep this circuit on by routing the emitter to the base?

I'm modifying a current-limiting circuit to work with a transistor instead of a switch. This circuit amplifies a voltage across a sensing resistor via a differential amplifier op-amp configuration. ...
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2answers
71 views

Why do we use one bias (VCC) for transistor amplifier circuits and 2 supplies for opamp circuits? [closed]

Opamps are said to have 2 supplies, so that the output can rail between these two points, then why do transistors have only one bias point.
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1answer
67 views

Transistor latching circuit

I have made the following circuit from a few online sources, it is very basic but uses two NPN transistors to make a latching circuit that toggles when either push button goes to ground. My Falstad ...
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1answer
76 views

NE555 and LDR circuit diagram

I have modified a schematic for my project with the following image: Instead of a 20K potentiometer, I use 100K for more precise adjustment. Do I need to add a disk capacitor of 10nf or 100nf to Pin ...
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2answers
57 views

is it possible to boost up the current by keeping the voltage constant?

I have a source that can deliver 20mA and 4.5V (MAXIMUM). I need to boost the current to 1 A without using any further source. Also, the voltage should be maintained constant at 4.5V. is that ...
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1answer
30 views

How can I detect that a ZVD-style 'backpower protection circuit' is operating correctly?

I'm designing a circuit that needs a 'backpower protection circuit', similar to what the Raspberry Pi HATs use. This is meant to block voltage from the secondary board when the primary board is ...
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1answer
93 views

Can a stepper motor flyback diode discharge a coil when connected in serial to the coil and opposite to the current?

On a circuit taken from this page http://www.opend.co.za/tutorials/steptut1.htm The last circuit shows two diodes positioned in reverse polarity to the current. It is supposed to protect against the ...
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1answer
57 views

Field effect transistors

Assume we have a field effect transistor.We connect the source terminal to the anode of a battery and the drain terminal to the cathode of a battery.We connect the gate terminal to cathode of a ...
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1answer
65 views

Why base emitter voltage (Vbe) of BJT is not showing as 0.7v in proteus simulation?

I was just trying to simulate a simple transistor circuit as common emitter in Proteus 8. However the I observe that the base-emitter voltage (Vbe) of the transistor 2N2222 is showing as 1.36v instead ...
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2answers
56 views

When is a Gate potential zero?

I have this fairly simple NMOS and it is mentioned that I can determine the Source current \$I_3\$ with the formula \$ I_3 = \frac{K}{2}(V_{GS} - V_{th})^2 \$. Here they equalize Gate Source Voltage \...
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1answer
67 views

NMOS High Side switch circuit solving

I'm trying to get my head around the circuit theory behind the high side NMOS switch, here is the shematics: My question is not about whether this is a good or a bad way to make a high side switch (I ...
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3answers
71 views

Controling Mosfet by 3,3V Raspberry Pi GPIO Pin

So I'm currently working on a project where I need an IR camera with two IR Leds attached to it. The camera looks something like this: https://rads.stackoverflow.com/amzn/click/com/B01ICLLOZ8 These ...
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1answer
69 views

Change in duty cycle of a transistor (BJT)

simulate this circuit – Schematic created using CircuitLab I have recently been working on a project in which my requirement is to transmit the data through a transistor, at a typical speed of ...
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2answers
3k views

What is the role of the transistor and diode in a soft start circuit?

Please can someone explain the purpose of both the transistor and diode in this soft start circuit
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4answers
148 views

Why won't this circuit work?

I made this circuit. I calculated everything, but all I get is THE LED JUST WONT TURN ON. simulate this circuit – Schematic created using CircuitLab
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2answers
56 views

Using transistor as switch in the “middle” of the circuit

I have an rather complex circuit with button micro-switch in the middle (actually, it's RF remote control with 3 buttons). I would like to be able to simulate the micro-switch click on it with one of ...
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2answers
50 views

What is the base current of a class ab amplifier with darlington pair configuration

I am trying to design a 3 stage amplifier using transistors, 2 pre-amp stages using class A configuration and an output stage class AB. I have built the class ab amplifier with a darlington ...
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0answers
46 views

Single-frequency AM Receiver?

Previously today, I tried to make an extremely simple AM receiver without a tuner. It didn't really work (I'm still trying to work on it), but I also tried to make an AM receiver that is tuned to one ...
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3answers
174 views

Simple AM receiver schematic?

I've been trying to make an extremely simple AM receiver (without even a tuner), however, it doesn't seem to be working. As shown in my schematic, what I did was connect the antenna wire to the base ...
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2answers
39 views

Triac switch cause of heating

As a newbie to hardware design, I'm having some trouble picking components. I want to switch a 24V AC Solenoid valve using a triac. According to my research/experience, transistors heat up during use. ...
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2answers
153 views

Drive 12V Automotive Relay from 3.3v ESP32

I am working on a project to start a vehicle using Automotive Relays. And I am following this circuit in the tutorial to do so. Everything works fine on Arduino UNO. But I want to use ESP32 of this ...
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2answers
442 views

Grounding Vcc and Vee?

I recently started electronics as my hobby. I'm working on this v/oct modular synth and in the schematic that I was working on, it did not make sence to me when all the Vcc and Vee are connected to ...
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1answer
48 views

LED cube using 74HC595 and 2N2222

So I'm trying to build an 8x8x8 LED cube according to this Instructables. But I'm using slightly different parts: 74HC595 shift registers instead of 74HC164 2N2222 transistors instead of 2N3904 I'm ...
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0answers
14 views

Replacement of DMP2215L P-Channel MOSFET with AO3401 from Alpha & Omega

I want to replace a faulty Diodes DMP2215L SOT23 p-channel MOSFET https://www.diodes.com/assets/Datasheets/ds31125.pdf with the p-channel AO3401 MOSFET from Alpha & Omega http://www.aosmd.com/pdfs/...
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1answer
39 views

LowPro proportional valve drive circuit clarification

Am new with amplifiers when trying to use them as a current controller so is just after some help in understanding the circuit. I am designing a circuit that will use a LowPro Proportional Valve ...
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1answer
59 views

Student problem: Amplification of cascade

I'm trying to find amplification of this configuration. I'm using small signal analysis but I'm stuck. I'm new to electronics so please have that in mind. Here is photo of my problem and my attempt to ...
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2answers
95 views

LED driven by MOSFET is dim

I have this schematic: I had to replace T1 transistor with a MOSFET (because D4 on an ESP8266 has to be high at boot time and the transistor reduces the pin voltage, so the ESP doesn't boot - see my ...
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1answer
71 views

Don't know which transistor I should use

I am new to transistors. I want to know which transistor I should use which will suffice for my H bridge. My motor draws 1.2A at 6V when stalled.
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2answers
36 views

ESP8266 GPIO2 - invert logic NPN transisotr

I make big mistake in my design. I connect output to ESP8266 GPIO2 at this pin I got base of NPN transistor to control LED. I test it on breadboard but probably by noise or "universe magic floating ...
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0answers
67 views

How does this negative voltage generator work?

I managed to fry a piece of moderately rare equipment due to connecting it to the wrong voltage power supply, and I'm now trying to diagnose what's wrong. Luckily, reverse engineered schematics are ...
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1answer
82 views

Resistor values on a 12v 10a circuit with LT3045 LDO

I am currently working on a project that aims to provide 12v 10a in the final output. I am quite new to EE and wasn't quite sure if I have choose the correct resistors value as highlighted in the ...
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4answers
1k views

What kind of transistor turns on with 0.2 volts?

I need a circuit to turn on a LED with 0.2 volts. I want to do it with a transistor as a switch. What kind of transistor will turn on at this voltage?
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0answers
66 views

Comparing sine wave and triangular for spwm using comparator

i am trying to generate sinusoidal PWM by comparing sine and triangular wave. First i just tried to compare sine wave with reference voltage in order to check the working of op-amp. I get a problem ...
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1answer
110 views

Driving IR led from 3.3V GPIO using 2N2222 transistor

I am using the following circuit to drive an IR led from a NodeMCU. simulate this circuit – Schematic created using CircuitLab However, im seeing the following on my scope. (Please ignore the ...
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0answers
41 views

Push-pull transistor - input current spikes and advantage over just an npn transistor

I have simulated the following circuitry in LTSpice: Input Voltage pulse characteristics: Questions: 1. What is the reason for the current spikes on the input resistor R2? Do I need to worry about ...
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1answer
61 views

NPN transistor won't saturate when Vcc is greater than 7 volts

Am I missing something here? I have an NPN transistor (2N2222) with a 10K resistor from collector to Vcc. Also a 10K resistor from base to input signal. Emitter is grounded. The base input is ...
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3answers
173 views

Why doesn't this battery voltage measurement circuit work? [closed]

So, I built this simple circuit for measuring voltage from a battery pack to an Arduino. The thing is, I want to measure the first cell and then the voltage from the whole battery pack: using two ...
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2answers
80 views

CMOS Inverter Circuit Analysis

So I have a circuit shown below, that looks to me likes it's a CMOS inverter circuit. In this question, we're asked to find the current and voltage across drain-source voltage of the NMOS component. ...
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1answer
46 views

Relay or Transistor as low DC switch

I am working on a project for a watering controller where I would need to turn on or off an solenoid valve (electric valve), my first thought would be to use a relay, but I know relays are good for ...
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1answer
75 views

Transistor identification

I have had a battery power bank from anker (powercore 20100mah) for some time now and it stopped working. Upon opening the case i saw a blown up transistor and i am having trouble identifying it. It ...
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0answers
83 views

Transistor current source \beta varies (AoE Ex. 2.23)

I am having trouble solving the following exercise: Exercise: If \$ \beta \$ varies from 50 to 100 for collector voltages within the output compliance range, how much will the output current vary? (...
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2answers
67 views

Low Signal from Single Transistor Pierce Oscillator Mysteriously Turns High

Yesterday, I was attempting to build a single-transistor Pierce Oscillator based on an old Application Note from National Semiconductor. According to the Application Notes, the following circuit was ...