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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41 views

Which biasing is better current or voltage? [on hold]

A transistor/differential amplifier/any other circuit can be biased with both voltage and current sources. So which one to chose and why?
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28 views

AC equivalent circuit -BJT

For the following circuit, I'm asked to give the AC equivalent circuit for small alternative signals. On the second circuit (the one they gave us as a solution), I don't understand why they didn't ...
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4answers
2k views

Why are there so many relays used in a car, instead of transistors?

Recently I did some work on my car electric circuits. I see many relays are used in car circuits. These relays are used for simple switching, and I wonder why these circuits are based on relays and ...
8
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2answers
1k views

Why would I use 2N3904 instead of 2N4401?

2N3904 and 2N4401 appear to be very comparable parts in all specs. 2N4401 has a higher current rating, but otherwise they look to be about the same in price and everything else. Obviously it's ...
0
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1answer
43 views

Common Emitter amplifier Bias Circuit Simplification

This is a slide from one of my semiconductor devices lectures. I understand how the bias circuit works and how to calculate the resistor values however I do not understand how this simplification ...
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1answer
54 views

Find the maximum of three sinusoidal voltages at any point?

Given three sinusoidal input voltages, I need to design a circuit to output the highest voltage, without using opamps. I honestly have no idea where to start, so would just appreciate any hints or ...
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3answers
105 views

How do transistors have three legs when there are two circuits going through?

I keep seeing a not-transistor outlined like this: But every picture of an actual transistor looks like this: I can't help but notice four lines exiting the diagram, but only three legs exiting ...
4
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3answers
114 views

Light an LED when load is in circuit

I want to have a LED light up when a load is in circuit, and go out when it is not. Initially I set the circuit up so that the LED is in series with the load but this didn't work. I think possibly ...
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1answer
90 views

Need To Understand Transistor Based Led Circuit

Which Transistor Topology Is Used in the Below Circuit & Why? Need to understand the purpose of zener diode (ZD2) with 12.5 Vz and R1 with 2k value? Why C1 & R2 is used for Q1 transistor? ...
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1answer
30 views

Switching a millivolt gas valve with a low-voltage digital timer

I have one of those old gas heaters that has a millivolt valve powered by a thermopile. I want to control it with the brain of a digital programmable outlet timer (minus the AC switching components - ...
0
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1answer
36 views

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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1answer
38 views

Drawback of RF BJTs

So when manufacturers build transistors they always have to trade-off certain parameters for others. RF transistors often have a high gain-bandwith product and low capacitance to make the gbw usable. ...
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1answer
25 views

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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1answer
79 views

pnp and npn circuit

I'm new to transistor field and I have questions concerning this circuit : simulate this circuit – Schematic created using CircuitLab what I understand: Q3 base must be at lower ...
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1answer
77 views

Evaluating the quality of photomasks

Photolithography would be new in our instituion and i could not ask any experts there about it, thats why i turned here. I have created a photomask using an electrolithograpy proccess and am now ...
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1answer
26 views

Intermittent Pulses in Anti-phase Step Generator

I've recently been studying some old circuits, in particular some of the Heathkit circuits and I'm currently looking at this one: IT-1121 Curve Tracer. Here's a snippet of the step generator which ...
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2answers
86 views

Switching +12VDC by arduino

I am new to electronics, so please bear with me. I have next task to do: I have programmed Arudino Mega 2560 to provide some arbitrary digital signals on predefined pins. This is to provide some kind ...
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0answers
53 views

Amplifying 1.5v to 3.7v using pnp or npn [closed]

is't possible to amplipy 1.5v to 3.7v using pnp or npn transistor. And how. How? Becouse i have All the requipment ready But to install the rorrectly in a circuit is main headache.
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1answer
54 views

Mounting through hole package on busbar

Through-hole components are not designed to be busbar mounted. But I have the need to use "laminated" busbar because of some factors (among others): High current Small parasitic inductance Power ...
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0answers
78 views

Replace BJTs with MOSFETs

Is there anyway to replace this Darlington BJT amplifier pair in this signal detector with MOSFETs instead? Perhaps using MOSFETs to amplify the current instead. I am trying to replace this Darlington ...
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1answer
35 views

how to find equations for current of circuit with transistors?

using Ohm's law, i need to find the current for $$I_C , I_B$$ in terms of: $$V_B, V_C, V_{DC1},V_{DC2}$$ for the following ciruit. my solution is: $$V_{DC2}+{I_B}{R_B}={I_C}{R_C}+{V_{DC1}}+{V_E}$$ ...
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2answers
64 views

Logic level MOSFET switch

I am trying to use a FET to switch on a boost converter. simulate this circuit – Schematic created using CircuitLab From reading I have found that people like to use IRFML8244TRPBF for ...
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4answers
85 views

Using a battery charger instead of a battery?

I have built a simple circuit with two diodes that light up intermittently. It requires 9V DC voltage to run. I don't have a DC source at home, and would like to avoid buying 9V batteries repeatedly ...
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2answers
34 views

12 volt switched by 5 volt

I have an issue with 12 volt DC LEDs installed on a 5 volt DC circuit. Switching must be performed as close to instantaneous as possible. So I searched around but nothing would do what I need. I ...
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1answer
36 views

Automatic LED lamp with sound sensor [on hold]

I have an auto light circuit with a sound sensor. The problem is when I try to simulate, this circuit does not work. Here is the circuit. I think the mistake is on the resistor is too large. then I ...
3
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2answers
58 views

What is the use of the line connecting drain and gate in current mirror using voltage bias?

I am confused about current mirror. Given this circuit simulate this circuit – Schematic created using CircuitLab it makes sense to connect the drain to the gate in order to make their ...
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0answers
34 views

Bipolar Transistors polarity

I have circuits problem where one part specifies that Vb is chosen such to forward bias the base collector junction by .2V. This tells me that Vb > Vc. With the information given I know that Vbc=.2 ...
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2answers
64 views

How do I stop/compensate for a voltage drop across a transistor? [closed]

I have used a 555 timer to output a pulsed signal with amplitude 4.6V. I am then inputting this signal into a transistor to pulse an led. When I do this the amplitude drops to 0.8V. How can I stop ...
3
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3answers
100 views

Cheap, low-quality constant-current sink over wide voltage range

I'm looking for a cheap (as in: low component count, low PCB area, low component cost) way to put >= 1mA of load on a voltage that may be anything from 1.2 to 17 volts (minimum required load on a LDO ...
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0answers
17 views

How to work out (Hie) input impedance for ZTX650 BJT Transistor?

Please can someone tell me how I can work out hie (COMMON EMMITTER MODE) for ZTX650 BJT Transistor. It is not anywhere on the data sheet. From all the research I have done, one website has told me hie ...
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1answer
23 views

Not gate dividing voltage

simulate this circuit – Schematic created using CircuitLab I am working on a binary calculator using 2n3904 NPN transistors. I noticed when using a NOT gate the voltage gets divided when ...
0
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1answer
24 views

How to work out (Hfe) AC Forward current transfer ratio for ZTX650 BJT Transistor?

Please can someone suggest to me how to work out the AC Forward current transfer ratio for this BJT Transistor (ZTX650 BJT Transistor) used in common emitter. I looked on the data sheet (herewith is ...
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2answers
117 views

Question about amplifier design

I'm somewhat new to analog circuit design, and I have some questions about this circuit, which I came up with trying to understand how transistor amplifiers work: simulate this circuit – ...
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2answers
51 views

Circuit completes whether base current applied or not - transistor

My fourth electronics project ever. The most challenging yet. I've wired up this project (Project 4 - Short Circuits project kit Jaycar Electronics). After much research, it doesn't do what I ...
0
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1answer
35 views

How to get the same output signal but with an increased capacitive load?

I'm designing a CMOS circuit of a VCO and it works perfectly fine when tested independently. Now when I cascade an other block like a divider to it, the output isn't the same as before. Rather its ...
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2answers
66 views

NPN Transistor circuit not functioning

So I'm making a simple circuit using a transistor as a switch, I've made these a bunch of times before without any sort of issue but for some reason this time it just doesn't seem to work at all. ...
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2answers
80 views

Transistor to switch a motor not working - what's wrong?

I've been working on a project and cannot seem to get it right. I'm using an arduino to control a motor, and turning it on and off via a transistor. I had an issue with it not working, so I posted ...
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2answers
121 views

Can current flow both ways through a transistor?

Last night I was experimenting with and motors and transistors. I was testing out NPN and PNP transistors to learn more about how they work and how I can use microcontrollers to control the speed with ...
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1answer
43 views

Heatsinking a TO 220 Case

There are modules that I have purchased that are already built on a PCB, and I would like to integrate them into my board. There is a TO-220 case which is a transistor on the bottom side, and it is ...
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0answers
34 views

Amp troubleshooting with clicking relais

Im having some trouble with my old Realistic amplifier. Out of nothing, my speakers started to make a repetitive (about once a second) full in and out movement of the cone, producing a deep bass ...
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2answers
43 views

add transistor model to LTspice

I'm trying to add the mmbt3904lt1g model to LTspice. - I've copied its data from the MMBT3904LT1.LIB.txt in the standard.bjt library. - I've added an NPN to my schematic then I've changed its value to ...
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3answers
39 views

Simple USB powered PIR sensor with LED attached to it (no arduino)

I'm new here and I'm re-new in electronic hence why I'm seeking for some help. Last time I touched a breadboard with a transistor was 10 years ago. So, here's my problem and the problem to the ...
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votes
2answers
122 views

Why do I need to know the current of the other device when using transistor [duplicate]

I have a LED lamp (it already HAS a power adapter), all I'm trying to do is turn it on using a NPN transistor (2N3904): Someone told me that I will burn my transistor or controller attached to the ...
3
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5answers
247 views

How to distinguish PNP and NPN transistors?

I need to know how to distinguish between an NPN transistor and a PNP transistor. If I pluck any transistor from a radio, how can I know its nature using a digital multimeter?
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1answer
44 views

NPN or PNP for multiplex seven segment display?

I want to put three multiplexed seven segment displays on a pcb module which then will be connected to another board through a 1x12 Pin header housing an ATMega (so assume in the following that Pin 11 ...
3
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1answer
39 views
0
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4answers
100 views

Is dependent source really a device?

Is dependent source really a device like a battery or is just a model as we model transistor with dependent current source?
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0answers
36 views

TP4056 - Increasing charging current

I am designing a Lithium Ion charging circuit that will be using the TP4056. Currently, the peak current is 1A, and I would like to increase the charge current in order to complete the charge faster. ...
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2answers
126 views

Not sure what two PNPs are doing

I've been delving into analog a bit more and am a little confused by a configuration I saw of two PNP BJTs. I saw two emitters tied together and then their collectors tied together through a ...
0
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1answer
55 views

Minimum voltage for a RC Oscillator

I am trying to run an RC oscillator using a 2n3904 the circuit looks like the following. You can see the live circuit here. Simulation I want to run it at 0-5v but I am not getting the result, I ...