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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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Mosfet pinchoff, why the n-channel moves towards source?

Suppose we have an NMOS transistor with VGS> VT. When VDS is 0, the channel depth is uniform along the transistor. However, when we increase VDS, the channel becames deeper near the source and ...
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4answers
80 views

analysis of BJT PNP type - why they can use voltage divider?

Hi everyone, I try to understand why some books used in a voltage divider to find the Base Voltage? or maybe the right question is HOW they can use voltage divider if there is base current? what I ...
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30 views

charge capacitor in two phases

i want to charge two 25F Supercaps (in series) in two stages: while their total voltage is under 5v, i want to charge them slowly via a resistor R3 of around 100 Ohm. After they reach the desired ...
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45 views

What is the purpose of a transistor? [on hold]

I've been studying about diodes and transistors and something made me wonder about the purpose of transistors. In the examples we were talking about increasing current by using two batteries with a ...
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53 views

Parallel Transistors Current Sharing

If we have a linear power supply, which uses parallel power transistors (NPN) as series element, with emitter current sharing resistors, then which is the maximum acceptable difference of current ...
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43 views

Joule Thief Modelling

I Try to use a joule thief circuit to harvest energy from almost die battery. But the reference that i found on forum or conference paper just explain how joule thief circuit works, not the ...
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1answer
48 views

Open circuit voltage gain of JFET transistor circuit

So this is one of the questions from my previous past papers, I worked out my Vgs and Vds value correctly (-1.25v and 10v). However, when calculating my open circuit voltage gain, I use the equation ...
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34 views

Diode and transistor choice for small solar energy-harvester [on hold]

I make a small solar energy-harvester with the input is 0.7V-2V (150uA-200mA). My Solar cell produce 2V 200mA when the light is bright and produce 0.7V 150uA when the light is low. I used self-...
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1answer
25 views

Mosfet or bjt choice for low voltage joule thief application

I make solar energy harvester using joule thief circuit with a small solar cell as the input. The output voltage from the solar cell is 0,5V. But the generic transistor, exactly silicon material need ...
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0answers
52 views

MOSFET switching on

I have a doubt. Consider an N-MOSFET: which is the voltage that can switch on it? The voltage between Gate and? Sometimes I read "between Gate and Bulk", sometimes "between Gate and Source", sometimes ...
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4answers
126 views

What is the purpose of using the transistor in the circuit?

Current sensor using an instrumentation amplifier: Image source: Texas Instruments INA139, INA169 High-Side Measurement Current Shunt Monitor, Typical Application Circuit (datasheet page 1) Could ...
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2answers
28 views

How to connect a device to ground using negative signal with high impedance

simulate this circuit – Schematic created using CircuitLab I have a device that enables a ground connection when I press a key on a remote control. This negative signal used to control other ...
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2answers
37 views

24V signal switching optccoupler

We have a robot, and it has 32 digital output, fed into a homemade PCB. On the PCB we have optocouplers, which have a forward voltage around 1.2-1.3V. So I need to drop the voltage a lot. That's why ...
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3answers
84 views

Using Op-Amp to amplify DC?

In all the textbooks the shown inputs to Op-Amps are AC. Could one use Op-Amp to amplify a DC voltage? if the answer is no, why not? Why only transistors can be used to amplify DC, aren't Op-Amps ...
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1k views

relative price of a transistor and a capacitor

DRAMs achieve high memory density by storing each bit of information with one transistor and one capacitor. That got me wondering, how expensive is a capacitor relative to a transistor?
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89 views

Does current drive voltage in a transistor?

I have this circuit, but I want to know how much voltage will be dropped between base and emitter of the transistor, and how much over the 1k resistor on the left. Since a transistor does not have a ...
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1answer
85 views

What is the role of the rightmost transitor in this circuit?

I extracted the following circuit from an schematic. It is part of power section. The switch on the +2V line is actually a GPIO from a microcontroller which turns to +2V when powering on the device. ...
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1answer
38 views

Simple battery backup [closed]

I am experiencing sudden outage in my area from few seconds to a hour or so. I am currently using this circuit. Turning on and off every time for a blackout is just annoying. I just want to cut off ...
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2answers
48 views

Low power dual edge detector using too much power

I am creating a hobby circuit which transfer signal to edge triggered pulses. I created circuit like this: But I have issue with power consumption. XOR gate need power which take 8mA which is really ...
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2answers
71 views

How current is steady after pinch off voltage?

I was studying the JFET. In the books and other material it is mentioned that when the voltage between the drain and source is increased then drain current is also increased. After a certain point (...
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2answers
65 views

Wireless Electricity Transmission model not working. Why?

I made wireless electricity transmission model using the principle of magnetic inductive coupling to transfer electricity between two separate coils. The model is very simple, known to everyone and ...
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1answer
47 views

BQ2002 NiMH Charging Circuit not working

I have the following charging circuit based on the BQ2002 which will charge a NiMH battery using a 5V micro USB cable. I built the circuit already and noticed that the TIP32C is not getting hot and ...
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2answers
49 views

Switching circuit transistor NPN, load has voltage and current though transistor is off

I am confused about the switching of this circuit. I can control the V1 input line. Output line is R4 load line. My Vbase (V1) is 0V, and Vbe is 0V. Transistor is off and collector should see 0V. That ...
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1answer
29 views

electrons of the collector in NPN transistor

What happens to the electrons in the N region of the collector of npn transistor that operates in active mode ? I know that electrons coming from emitter split to base current and collector current ,...
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3answers
78 views

can I build a multiplexer with just four transistors?

Some time back I found a circuit on the Internet that professed to build a logical OR gate with two transistors; accompanying it was a circuit that professed to build a logical AND gate, also with ...
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2answers
87 views

Not enough current draw through MOSFET

I am trying to control the current to a Raspberry Pi using a MOSFET and an ATtiny10. I am using a logic level MOSFET and it seems that the Pi needs about 250mA to turn on but it is only able to pull ...
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2answers
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trying to figure out the differences between the six transistors provided by the schematic tool [closed]

My background consists of a BS in Computer Science and an MS in Computer Science and Engineering, both from the University of Washington. My MS consisted mostly in the very high level design of a ...
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3answers
80 views

Is there no current between these terminals?

This is related to charge carries movements out of transistor terminals. Assuming a transistor in common emitter connection is biased properly where resistors are omitted for simplicity. Before asking ...
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1answer
36 views

Equivalent power BJT transistor 2sa758 and 2sc898 for Sansui au 6600 Amplifier

I am restoring my Sansui au6600, at the moment I am recapping it, however I will have to replace the two final power transistors for the left channel which I found out to be faulty. The parts listed ...
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1answer
43 views

Output characteristics of a CE Transistor

In the saturation region the emitter base junction and collector base junction both are forward biased.It is said that in this region Ic does not depend upon the input current Ib .Why is it so?Explain....
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1answer
75 views

PNP Transistor Switch for Relay

simulate this circuit – Schematic created using CircuitLab Hi, I have a low battery detection circuit here. When the voltage of the battery goes below 10.5, I have an LED flashing (Uses the ...
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4answers
73 views

Why does the base-emitter voltage in NPN transistor become constant?

The setup above shows the experiment that I have been working with. During the experiment, the current \$i_c\$ and the voltage \$V_{be}\$ were measured for increasing \$V_{in}\$. At some point, the ...
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1answer
41 views

Gilbert Cell Output Current

I do not understand the basic of a Gilbert cell. I see that as its output we consider the output differential current Io. But I do not understand it. Is the load connected between the points 1 an 2? ...
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2answers
78 views

How do I know that this BJT is in the saturation zone without having to simulate it?

I have to find the working zone of this BJT, for different values of P, by using a simulation software like Simulink. But I would like to know how to do it manually. The way I learned is sort of ...
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1answer
68 views

Cascading Op Amps for Phototransistor Output Conditioning

I am working on a project in which I am using an IR phototransistor to detect changing low levels of light. Currently with very high load resistance I can get a reading of 40-60 mV but I would like to ...
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72 views

I need a low voltage high current switch [closed]

I am working on a school project involving high current and low voltage. I must switch 2.7V and 150A and I can't manage to find any solution for it. I was thinking of a MOSFET but I don't think it ...
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2answers
32 views

Explain how this astable chain(?) circuit works

The circuit below fades on and off a cascading series of leds in an alternating fashion. I tried reproducing it on a breadboard with 5 leds to try to understand it how it works, and got all sorts of ...
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1answer
71 views

Working region of NPN BJT

I have come across the following circuit where a BJT works as switch when I apply 23 volts to base using a 100k resistor. A 3.2 mA constant current source is connected to the collector of the BJT ...
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43 views

Common emitter with current mirror biasing

I'm having some trouble understanding the current mirror. When I thought I understood it, I had trouble using it as a biasing method. What I don't understand now is: Why do we use a PNP mirror with ...
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2answers
150 views

Does a transistor have resistance?

If a transistor is in the "active" region and the current to it's base -> emitter is reduced, will the resistance between collector -> emitter increase in a proportional way?
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3answers
890 views

How to avoid secondary breakdown effect in transistor?

I have a transistor circuit with relay control (as shown) Transistor base is controlled via micro controller output. The problem is, some time switching relay cause micro controller to restart. ...
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2answers
2k views

Transistor gain, what if there is not enough current?

I understand that a transistor will amplify current by a certain gain factor if it is below saturation. But what if there is a resistor that reduces current? So let's say there is 1mA between base ...
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4answers
762 views

TIP120 Transistor + Solenoid Failing Randomly

I am using TIP120 transistors (controlled by 74HC595 shift registers) to control 12VDC, normally closed solenoid valves. Everything is working in short-time tests however when left overnight, some ...
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0answers
73 views

Mosfet not turning off when gate is grounded

I have a FQP50n10 mosfet which I used to drive an Arduino and it was working great. For the past few months I've been trying to make a circuit but it’s not working with the values I want because I’m ...
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2answers
84 views

modify schematic to work at 5V (solar panel sun tracking system)

I have this schematic and I want to know: if it will work at 5V (my solar panel is 5V-6V) modifications required to command (clockwise/anticlockwise rotation) the motor directly with the final ...
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3answers
106 views

What happens if we force a voltage on Vbe of a bjt transistor

I'm wondering what happens in a BJT transistor if we force a voltage bigger than 0.7V on Vbe. A colleague of mine said that if we put on Vbe, let's say, 5V the transistor would be saturated. I ...
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2answers
62 views

Transistor functionality in a given schematic

Can anyone tell me what is the functionality of the transistor in this schematic ?
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2answers
114 views

How do I draw a transistor with a circle at the base?

I've seen schematic diagrams with transistors that have a little circle right where the gate connects with the rest of the transistor. From the context it seems like the behavior is that the ...
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1answer
90 views

Transistor as a switch for 3A collector current

I am using: ATtiny10 w/ 10Ohm Resistor in series to drive Base of transistor Transistor is ZTX688B Vcc is 5V and 3A source Load is a Raspberry Pi connected to Collector simulate this circuit –...
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1answer
75 views

2N2222 transistor datasheet saturation current

I am designing a 2N2222 transistor common emitter voltage-divider amplifier. Using 9V for the power supply and trying to make the loadline to determine Q. How do I determine the sauration point ...