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Posts tagged transistor

Synonyms: transistors

Subtag of semiconductor-device · 2 child tags

Anything related to transistors, a broad category of active electronic components based on semiconductors (they are semiconductor devices).

The most common kinds of transistors are BJTs and FETs (JFETs and MOSFETs).

Use this tag for questions related to transistors in general. If your question is exclusively about a specific kind of transistor, just use the more specific tag (e.g. BJT, MOSFET, etc.).

This tag doesn't have a detailed wiki yet.

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Q&A Calculating base voltage of NPN transistor

I'm having trouble using the nodal equations to determine the base voltage Vb1 in the circuit below. I've attempted to write seven equations below, but not able to fit them in entirely. (12-Vx)...

2 answers  ·  posted 9d ago by kadamrohan16‭  ·  last activity 8d ago by LvW‭

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Q&A Control logic for mosfet in piezoelectric energy harvesting circuit

I'm working on an energy harvesting circuit known as an in-house harvesting circuit (cc-ih) and would appreciate some guidance on implementing it in Simscape within Simulink. Circuit Description: ...

2 answers  ·  posted 1mo ago by losdox‭  ·  edited 1mo ago by Nick Alexeev‭

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Q&A MOSFET drain current ringing in saturation region

I benchtested below 0.7A constant current source circuit and observed few cycles of oscillation on drain current. With the help of bode plot analysis , I have managed to reduce the oscillations on ...

2 answers  ·  posted 2mo ago by kadamrohan16‭  ·  last activity 2mo ago by Olin Lathrop‭

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Q&A Matched transistors

There are circuits that require matched transistors. Whether BJTs or FETs. Like current mirrors, logarithmic amplifiers, etc.. There are some examples: https://www.youtube.com/watch?v=DUlugLSroN8...

1 answer  ·  posted 3mo ago by Chupacabras‭  ·  last activity 3mo ago by Andy aka‭

Question transistor
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Q&A Soft-start circuit behaviour

Let's take a soft-start circuit that looks like this: To my understanding, the function can be described as follows: C1 charges to open the gate. Value of C1 will dictate the soft-start delay...

1 answer  ·  posted 9mo ago by Mu3‭  ·  last activity 8mo ago by Olin Lathrop‭

Question MOSFET DC
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Q&A Case temperature of MOSFET

Homework problem A MOSFET has a power dissipation of $P_{d} = 10\text{W}$. The MOSFET is mounted on a heatsink. There is an isolation pad between the MOSFET case and the heatsink. We are given t...

1 answer  ·  posted 2y ago by Carl‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A What is this fourth connection in NMOS device?

I know that in transistors there is base, collector and emitter, and in FETs there is gate, drain and source, but what is the fourth grounded connection opposite the gate in this NMOS circuit?

1 answer  ·  posted 2y ago by NMOS lover‭  ·  edited 9mo ago by Lorenzo Donati‭

Question MOSFET
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Q&A Battery protection circuit

I am using two 18650 cells in series to power a RC car. Is the voltage goes below 6.2 V, the battery should be disconnected to prevent over discharging the battery. At the same time I want to imple...

2 answers  ·  posted 2y ago by Stefan‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A How to change the polarity of an input using a single switch?

I have an mcu pin and I want to sense a voltage up to 24V to 36V. I want to connect some outputs on the board I'm designing and I don't know whether those outputs will provide a voltage or will be...

1 answer  ·  posted 11mo ago by DeadMouse‭  ·  edited 9mo ago by Lorenzo Donati‭

Question microcontroller BJT
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Q&A Is a BJT 3-transistor Wilson mirror faster than a simple mirror?

My question is trying to understand if there is an effect on the switching time, on both turn-on and turn-off, between the following configurations. A mirror set up to switch a current, and there ...

1 answer  ·  posted 3y ago by Pete W‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A How building a follower satisfying rather extreme requirements.

What is your best suggestion for building a follower that would ideally satisfy the following spec: frequency: from 100 Hz (or lower) to 1 GHz input signal impedance: 1 Mohm input signal ampli...

1 answer  ·  posted 3y ago by coquelicot‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A Thévenins Theorem for Transistor Circuit

I am calculating the base current of transistor Q1. To simplify the circuit equations, I applied the Thévenin's theorem twice and converted V1, R1 and R2 into Vth and Rth, as shown in the image. ...

2 answers  ·  posted 2y ago by kadamrohan16‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A PNP Darlington pair as a current limiter

I am trying to analyse what is controlling the load current in the below Darlington configuration. Is it the base current of transistor Q3 which is controlling current through R14 / emitter curr...

1 answer  ·  posted 2y ago by kadamrohan16‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A Purpose of emitter resistor in a common collector amplifier

I see a lot of common collector amplifiers with the output taken across an emitter resistor. What is the purpose of doing it this way instead of connecting your load directly to the emitter? I sh...

4 answers  ·  posted 3y ago by jm567‭  ·  edited 9mo ago by Lorenzo Donati‭

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Q&A Two way circuit breaking capability for ideal diode controllers

I would like to save some costs with ideal diode controllers. Basic requirement is for the diode controller to block overcurrents (short circuits) in both directions. The MAX16141A IC can do it a...

1 answer  ·  posted 10mo ago by kellogs‭  ·  edited 10mo ago by kellogs‭

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Q&A Darlington or Sziklai configuration - why and when using complementary pairs?

Why does the Darlington or Sziklai configurations need complementary transistors? For these configurations, when should I use complementary pairs and when could I use not complementary pairs ?

1 answer  ·  posted 4y ago by coquelicot‭  ·  edited 10mo ago by Lorenzo Donati‭

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Q&A Why Ib=const. for BJT output characteristics Ic=f(Vce)

Introduction: In some books and other technical papers (also from universities) it is - surprisingly - still claimed that the bipolar transistor (BJT) would be a current-controlled element. This is...

4 answers  ·  posted 3y ago by LvW‭  ·  edited 10mo ago by Lorenzo Donati‭

Question transistor
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Q&A Why there is a body diode in mosfets?

In theory (I mean in my engineering curriculum) I never found a diode in a mosfet symbol but in datasheets there is a diode called as body diode in both pmos and nmos.Please explain its significan...

3 answers  ·  posted 3y ago by aditya98‭  ·  last activity 10mo ago by Lorenzo Donati‭

Question MOSFET body-diode
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Q&A Complementary transistor pairs - what is the point ?

I understand that some applications require NPN-PNP pairs with identical electrical characteristics. But I would like to understand why.

2 answers  ·  posted 4y ago by coquelicot‭  ·  edited 10mo ago by Lorenzo Donati‭

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Q&A Thermal stability coefficient [closed]

The thermal stability coefficient is defined to be: $S = \frac{dI_{C}}{dI_{CBO}}$ where $I_{CBO}$ is the reverse current of the BJT when voltage isnt applied to the base of the BJT. In case of a ...

0 answers  ·  posted 1y ago by MissMulan‭  ·  closed 10mo ago by Nick Alexeev‭

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Q&A Are a JFET's Idss and Vgs(off) values correlated?

I know that many JFETs parameters have a very large manufacturing spread, in particular, $I_{DSS}$ and $V_{GS(off)}$, as one can see (for example) in this datasheet excerpt: ... My question i...

1 answer  ·  posted 11mo ago by Lorenzo Donati‭  ·  edited 10mo ago by Nick Alexeev‭

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Q&A Choosing between common-drain JFET amplifier, and common-source

Do common-source JFET amplifiers have an advantage over common-drain? The JFET would be in a low noise photodiode amplifier. The signal is 100us pulses with 10us raise times. Here are the schema...

1 answer  ·  posted 11mo ago by misk94555‭  ·  last activity 11mo ago by Olin Lathrop‭

Question JFET photodiode
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Q&A Sensing 3 states in a single mcu pin using firmware

I want to sense 3 different states in the same mcu pin (GND, Hi-Z and PWR). PWR is typical +24V but I would like to have a wide margin from +17V to +40V just to be safe. The values can change but ...

1 answer  ·  posted 11mo ago by DeadMouse‭  ·  last activity 11mo ago by Olin Lathrop‭

Question MOSFET
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Q&A Variant of a Mosfet's Gate-Source protection

Let's say a 100V voltage spike arrives at +12V and the TVS diode clamps it to 25V. Q2 may or may not be activated. Will this circuit ensure a V_gs lower than 25V for the mosfet Q1 ? Any catch to it...

1 answer  ·  posted 11mo ago by kellogs‭  ·  last activity 11mo ago by Olin Lathrop‭

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Q&A MOSFET protection with TVS: at the source pin or at the drain pin

In the auotmotive context, does it matter where the fat load-dump grade diode is placed in relation to the MOSFET so as to protect it from both fast positive transients and the longer load dump ? ...

2 answers  ·  posted 1y ago by kellogs‭  ·  last activity 1y ago by Lundin‭

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Q&A BJT common emitter amplifier equivalent circuit (π hybrid model) [closed]

Im studying the equivalent model of a BJT common emitter amplifier at high frequencies.At university we tought that the BJT at high frequencies looks something like this: However when designing ...

0 answers  ·  posted 1y ago by MissMulan‭  ·  closed 1y ago by Olin Lathrop‭

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Q&A Small signal analysis of BJT in saturation region

The small signal analysis of a BJT when the BJT is in amplification mode: is easy.However what happens when the BJT is in saturation mode? Can we replace the dependent current source with a r...

1 answer  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

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Q&A Re model of transistor is the same in 2 different configuration

I was studying the Re model of a transistor: But the Re model for 2 different configurations (common emitter and common base )turns out to be the same! I don't know why I am really confused.How...

2 answers  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by LvW‭

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Q&A DAC controlled high side current source.

I'm designing a high side current source that can be controlled with a Digital-to-analog and can source up to 100mA with voltage supply up to 36V. By high side I mean one side of load will be alwa...

1 answer  ·  posted 2y ago by DeadMouse‭  ·  last activity 2y ago by Olin Lathrop‭

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Q&A Why are there more N type than P type MOSFETs?

I was looking at different transistors, especially MOSFETS and I saw that N type MOSFETs seem to be way more popular to be used in circuit design. Is there a reason for that, or am I mistaken?

2 answers  ·  posted 2y ago by crusadEEr‭  ·  last activity 2y ago by Olin Lathrop‭

Question MOSFET
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Q&A Low-frequency PWM-controlled Mosfet heater circuit

The circuit above is used to control a 240W ceramic heater by means of a PWM signal at 30Hz, generated by a microcontroller, with 5V logic. The input is a standard 280W AC-DC external power adapt...

2 answers  ·  posted 2y ago by francesco‭  ·  last activity 2y ago by Pete W‭

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Q&A MOSFET not turning completely off

Hello everyone, I have a simple circuit in which I control some LEDs via an MCU and DMG2302UK ( N-channel MOSFET ) The EN pin is connected to an MCU gpio pin that works at 3.3V. The circuit wo...

1 answer  ·  posted 2y ago by AhmedMobarez‭  ·  last activity 2y ago by Olin Lathrop‭

Question MOSFET
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Q&A Confusion with Wikipedia article on multivibrator circuit [closed]

A while ago I made a question about the monostable multivibrator .Lets get a picture of it: When switch is closed it enters its unstable state and it eventually returns to the stable state Howe...

0 answers  ·  posted 2y ago by MissMulan‭  ·  closed 2y ago by Olin Lathrop‭

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Q&A Help with differential to single ended voltage converter

Hello I don't understand how this differential to single-ended voltage converter can work. What I don't understand is why we place a current mirror(a current mirror copies the current flowing thr...

3 answers  ·  posted 3y ago by MissMulan‭  ·  last activity 2y ago by Circuit fantasist‭

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Q&A MOSFET differential to single ended converter intuition

How does the differential to single ended converter work? In order for the circuit to work, Q1 and Q3 must be in the saturation region and depending on the voltage inputs, one of Q2 and Q4 will be...

1 answer  ·  posted 3y ago by MissMulan‭  ·  edited 2y ago by Peter Mortensen‭

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Q&A What is the difference between emitter and collector of a transistor?

In all descriptions of how (non-FET) transistors work I've seen, there is an inherent symmetry: There's either an n-doped layer between two p-doped, or a p-doped between two n-doped, and the descri...

2 answers  ·  posted 2y ago by celtschk‭  ·  last activity 2y ago by Olin Lathrop‭

Question transistor
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Q&A Battery voltage: to boost or to connect in series.

Background. I have a legacy battery system that is comprised of twenty-four 12V Li-ion battery modules (self-protected), enclosed in a shell with the charging connection provided as a common groun...

1 answer  ·  posted 3y ago by DSI‭  ·  last activity 3y ago by Olin Lathrop‭

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Q&A JFET equation of current

Is this equation valid only when a JFET in saturation mode , correct? because in the ohmic region the JFET acts like a voltage controlled resistor and increase in VDS increases the resistance of th...

0 answers  ·  posted 3y ago by MissMulan‭

Question voltage current JFET
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Q&A High Power Switch - High Side vs. Low Side Switching

Imagine a battery pack with <=60VDC of maximum voltage and a load of up to 10kW of power(the PMSM inverter with the input capacitance of up to 1mF). The load is not always known - could be 100uF...

2 answers  ·  posted 3y ago by 2kind‭  ·  last activity 3y ago by Olin Lathrop‭

Question MOSFET switching
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Q&A Using FET based followers and design rules

Usually, voltage followers are built with bipolar transistors (or with opamps if better precision is needed). In this case, the simple rule says that the transistor emitter "follows" the input vol...

5 answers  ·  posted 3y ago by coquelicot‭  ·  last activity 3y ago by TonyStewart‭

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Q&A How to define Vsat for MOSFET as a switch?

I was looking at this design: It uses MC34063 as switching controller. I wanted to adapt this circuit, and I was busy trying to pick R1 value. The datasheet has following formulas: The issue I hav...

2 answers  ·  posted 3y ago by Kranulis‭  ·  last activity 3y ago by Andy aka‭

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Q&A How to avoid shoot-through in MOSFET bridge drivers

I'm using a variable duty cycle square-wave oscillator to drive a half-bridge MOSFET pair like this. Upper MOSFET is P-channel type, lower MOSFET is N-channel type: - And, I think I'm getting shoo...

1 answer  ·  posted 4y ago by Andy aka‭  ·  last activity 4y ago by Andy aka‭