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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How Q11 works when Base is 0v?
why base Q11 is 0V current is flowing into the base of Q11, allowing current to flow between the collector and emitter.
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1answer
30 views
Transistor module and its maximum allowable power dissipation
I have a question regarding the selection of transistor modules. These modules often have a parallel diode. When calculating the losses and thus the expected heat development, I am not sure how these ...
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1answer
35 views
Switching based on voltage
I am trying to figure out the supply voltage for an 12V induction probe. The probe requires 12v and the supply could either be 12 or 24v. Currently, I have a SPDT switch to manually choose the supply ...
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41 views
How does this timer 555 circuit work?
Is this the way this circuit works ?
Vcc = 15v
With vref = 5v on the pin #5, then Vthreshold = 5v, and Vtrigger = 2.5v, meaning that
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1answer
70 views
Two-stage transistor amplifier
(sorry for the wall of text, I tried to give as much Info as possible)
I am pretty new to electronics and am working on a project regarding controlling the flow of a pump (BLDC based). End goal: ...
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1answer
55 views
How do I create a portable, battery-powered relay that switches in the daytime?
I have been trying to make a (hopefully very simple) circuit for this that just uses a couple resistors, diodes, and transistors that can fit on a small breadboard and be powered by a 9V battery. ...
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How does this timer 555 and transistor circuit work?
Is this the way this circuit works ?
If vref = 5v on the pin #5, then Vthreshold = 5v, and Vtrigger = 2.5v
With Vthreshold = 5v, if voltage on pin #6 Vp6 > 5v, then Vp3 is Vo = 0
With Vtrigger = ...
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61 views
How does only transistor and inductior without a capacitor oscillator work
It has been more than 10 years, I left electronics. I saw this circuit of wireless power transfer, it has to do with induction, but the oscillator circuit shown doesn't contain a capacitor. can anyone ...
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2answers
97 views
Why does a differential amplifier need two transistors?
This probably has a really obvious answer, but it's bugging me, so here goes.
Why do we need two transistors for a differential amplifier? Instead of of using a basic differential pair, can't I just ...
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What is value of Reverse Saturation Current (Is) for BC547B NPN transistor
I am trying to evaluate Ebers Moll equation for estimating collector current for a given V_BE at DC conditions. The datasheet of BC547B (which I am using) does not mention the Is (i.e. Reverse ...
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2answers
58 views
confusion regarding bias voltage of a transistor
"this dc voltage is known as bias voltage and it's ...regardless of the polarity of the signal source"
now I have this question :
**1.**Do i manually need to choose bias voltage so that so ...
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42 views
Why do these two nodes in these two circuits have different values?
In the second circuit, the diode and the resistor are in parallel, so why is the voltage at Vbq is Vr5q-Vbeq but not like the first circuit the voltage gets divided by the parallel resistance?
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69 views
PNP high side switching with 100 mA load
I have this circuit to detect tamper status using a switch. When the switch is pressed (ON) then GND is provided to the base of Q3 (2N3906), so that transistor will be in the saturation region and can ...
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3answers
141 views
Which semiconductors are good candidates for constructing a CPU? [closed]
Wikipedia offers an excellent list of semiconductor materials but does not include which can be used to create integrated circuits or even logic transistors (PNP or NPN). The Integrated Circuit page ...
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74 views
Notation in transistor circuits
These two figures(below) are from book Microelectronics circuits by Sedra/Smith.
I have two doubt regarding notation used in this book (or may be in general also)
1.in this figure(1) why there are ...
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1answer
37 views
Drive a DC Motor with a WS2811 chip
I'm building a robot that needs a lot of small hobby motors (or similar) to operate in sync. I was looking for ways to have as many of them controlled by a single source of truth as I am not sure I ...
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1answer
78 views
Constant current limiting circuit
Can someone help me understand the working of this circuit:
My questions :
Please explain me how this circuit will work in its entire operation range.
I am not able to understand the purpose of the ...
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2answers
55 views
Constant current LED driver using transistors
I have this circuit:
I understood the operation:
On power-up Q1 and Q2 are off. There is no collector current so L1 is off.
If the digital control input on the left is brought high (5 V) Q1 will ...
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1answer
36 views
Charging time of capacitor when used with this transistor configuration?
I´m trying to calculate the charging time of the capacitor in this circuit.
I know the PUT is on when the voltage in the anode is higher than the Vp
...
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1answer
42 views
Is the voltage on the resistor always low when the zener diode is not in reverse operating region?
I´ve read that the zener diodes are used for voltage regulation, and the resistor in this circuit limits the current through the diode and drops the excess voltage when the diode is conducting.
Does ...
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1answer
84 views
Is all that matter inside a chip the wires?
I was talking to a friend earlier about a class I'm thinking of taking. However, he warned me against taking it. The class is about chip design, microelectronics, and the physics behind them.
He said ...
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59 views
Controlling mosfet with a battery-powered attiny85
I have to control a MOSFET in switch mode. However, the whole circuit including AtTiny is powered by a LiPo battery. AFAIK AtTiny's output pin voltage is somewhere between 0.8*Vdd and Vdd and I'm ...
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49 views
BJT Active Region - Biasing of BE and BC junction
I am having trouble understanding why the BC junction is considered to be reversed biased in these two models. The way I see it, the base looks to be in a higher potential than the collector junction ...
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40 views
How does forward biasing of both junctions in BJT leads to saturation?
As far as I know, for an NPN-BJT, when both (base-emitter and base-collector) are forward biased; we consider the operation to be in saturation mode. Here, the transistor functions as a short circuit ...
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3answers
65 views
Dependency of Collector current in common base transistor(active region)
I just started reading about transistors from book "Microelectronics circuits"by Sedra/Smith,
This is written in book which I don't understand, any help would be much appreciated
For forward ...
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1answer
50 views
Transistor characteristics in a file
I'm creating a simple circuit simulator application. Is there somewhere a csv/xml/... database of diode and transistor characteristics?
It would be a great help for me.
Thanks in advance
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wien bridge input impedance
I want to know the input impedance at transistor T1's base.
1/Z=1/R4+1/R+1/Rin and Rin=beta(re+RE)
But how do I calculate RE ?
My guess : R3 is 0 because the wire at T1 collector is removed, thereby ...
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0answers
55 views
Output transistors on the TL494 [closed]
I am building a SMPS with a TL494 and got stuck on the output transistors to drive the gate drive transformer.
I have tried circuits with common emitter and common collector but somehow it doesn't ...
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1answer
118 views
Transistor with floating base
How does a transistor work in a circuit if its base has no connection to any part of the circuit?
How can I find its working state?
Thanks in advance
Edit:
Yes, this is a BJT. My assumption is that ...
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1answer
45 views
Why can you measure input and output impedance of a amplifier circuit with a resistance/potentiometer?
While running simulations for a circuit I measured the input and output impedance by simply adding a potentiometer, turn it up until the voltage peak to peak signal going out reached half and then ...
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39 views
Ce stage amplifier
I wanna design a ce stage amplifier with this specification :
Gain 20
Rc=10k
Max swing
The simiulation of the circuit is not the same with may calculations,
How can i solve this?
what i get from ...
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2answers
1k views
24 V transistor switch acting strangely
I am working on a project to switch a spring-applied brake (datasheet, page 84, MCNB 2GR) using a Teensy 3.5.
I only have limited electronics knowledge and am struggling with weird behaviour from the ...
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1answer
29 views
Selecting between 60V source and 1uV measurement
My goal is to perturb a sample with a 250us pulse of 100mA at 60V, then on the same probes measure the response over time in microvolts. The pulses will be repeating at about 100Hz, so most of the ...
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1answer
103 views
MOSFETs not activating - is this transistor the problem and can it be subbed?
I'm trying to repair a DC motor controller that moves a caravan. The positive side is relay switched, and it turned out that the negative side of the motor supply was switched by a pair of IRF3205 ...
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1answer
96 views
Can someone explain this part of circuit from BQ500212A?
As the title says, I am struggling to understand what this part of a circuit does. It's part of this evaluation module.
Is there any chance the BSS138 transistors will activate without the SNOOZE/...
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5answers
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How is quality/damage control done in large circuits?
There is apparently more than 28 billion transistors in the recently released Nvidia GeForce RTX 3080.
First, when you manufacture such a circuit there must be a decent chance of botching some of ...
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How does this tone generator circuit work?
I'm an electronics newbie who just started experimenting with the Snap Circuits style kit and I came across this high-frequency oscillator circuit.
When I put it together, I hear a middle to high ...
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1answer
44 views
PSpice models for BC547C, BC557C, BF245A, BC548C and BD135-16
I'm trying to make this circuit in OrCAD Capture CIS to simulate it in spice:
I found the resistors and capacitors in the ANALOG library. I also found all the transistors, except Q3, in the ...
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3answers
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Switch polarity on LED
I have an LED (don't know the part number unfortunately) that lights up red when its anode is tied to Vcc and its cathode to Gnd, and when the polarity is reversed, it lights up green (opposed to some ...
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26 views
Switch video sync signal using transistor
I have a circuit that currently outputs either a high or low signal from a pin on a PIC microcontroller. This part is working as expected.
I now want to take that high / low signal and use it to ...
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2answers
85 views
Using transistors to control a 555 timer in astable configuration
This is a condensed circuit used for hardware debugging purposes.
The goal of this circuit is to control the 555 timer with only three pushbuttons. I am using the 555 timer and resistors to simulate ...
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2answers
60 views
Calculation of the capacitor value across the base and emitter to avoid unexpected turn ON of transistor
There is a design recommendation to add a capacitor across the base and emitter of Q2 to avoid the unwanted/unexpected turn ON of Q2.
Calculation of new capacitor across Vbe:
My questions :
Can ...
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0answers
19 views
powerup and power down delay circuit
I have a customer requirement to enable and disable enable pin of regulator using GPIO. We a delay circuit in between. Delay is required both for powerup and power down condition. Can someone suggest ...
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1answer
34 views
Electronic Power Selecting Switch
I have a circuit which works with a battery normally. The nominal voltage of battery is 3.7 V and I am using boost converter to make it 5 V. And I have a charging circuit of this battery too. So, my ...
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1answer
71 views
Do capacitors limit maximum current in a circuit?
Do capacitors limit maximum current in a circuit when used after a rectifier? If yes, what's the formula for that maximum current?
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4answers
135 views
Roles of the coupling and bypass capacitors in a CE transistor
I wonder what the purpose of the coupling capacitors and the bypass capacitors are and the type of effect each capacitor has on the circuit.
As I've understood it, you use coupling capacitors to block ...
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2answers
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How is 1 bit transfered from RAM to a 1 bit register?
I've been reading on computer RAM and CPUs. I came to the conclusion that most RAM today use arrays of DRAM while CPU registers and caches use SRAM. 1 bit DRAM is a circuit with one capacitor and 1 ...
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Identifying the cause of defects in an H-Bridge by damaged transistors
I am preparing a fishbone diagram for reactive maintenance to be used as evaluative approach and part of it is brainstorming possible causes to get contributing factors.
Consider the following H-...
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3answers
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Reading Optocouplers datasheet: current transfer ratio (CTR)
So I am working with an optocoupler at the moment, and having trouble understanding what CTR value to use in my calculations.
The datasheet states 50% Min and 600% Max, which is a huge difference. Do ...
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4answers
60 views
Transistor circuit design review
I have a customer requirement where we have to design a GPIO controlled switch. We are using NPN transistor, where when the GPIO is high(3.3V) transistor is enabled and it acts as closed switch, when ...
