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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Why does reading the 3T1C DRAM cell is not destructive?

Could anyone help explain how the above 3T1C DRAM cell works? T means transistor and C means capacitor. And why reading it is not destructive? Thanks.
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76 views

Why does this transistor circuit work?

In the following circuit, why does a certain amount of current flow into the transistor in the below circuit? I can understand once the push-button switch is turned on, there would be current flowing ...
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2answers
63 views

How I can solve this BJT?

I edited circuit like this: I tried representing currents like: $$ \begin{aligned} &I_{R1}=100_{B1}+I_{B2}\\ &I_{R2}=101 I_{B2}-I_{B1}\\ &I_{i}=101 I_{B2}+100 I_{B1} \end{aligned} $$ ...
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42 views

BJT high frequency analysis

I have a little bit of confusion on how the textbook author is determining the high frequency cutoffs for the parasitic capacitance parameters for a common emitter amplifier. This is Boylestad ...
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1answer
114 views

Is this resistor routed correctly?

For a friend I'm trying to make a fuzz pedal and found this very flexible fuzz circuit, called "The Fuzz of 1000 Faces," at instructables, credits to Randofo. However, since it's an old post, I ask ...
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2answers
49 views

Transistor as a heater device and measured by LM35 temperature sensor?

The aim is to make a temperature control circuit using an Arduino Uno as a controller, an LM35 sensor as feedback to measure the actual temperature, a TIP31C transistor as actuator to control the ...
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1answer
44 views

Visual example of PNP transistor

Following this question, Visual example of NPN transistor, is the following a correct understanding of a PNP transistor? To be honest, I have no idea why the top of the transistor (where the current ...
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1answer
96 views

Visual example of NPN transistor

Is the following a correct understanding of an NPN transistor? Basically, a positive voltage source needs to flow through the Base of an NPN transistor and out through the Emitter, so it needs to ...
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1answer
35 views

Requirements for NPN, PNP transistors

Is the following a correct understanding of what makes a NPN/PNP transistor turn on or off? NPN (more common) Must have voltage > ~0.7V on base Must have (conventional) current flowing into ...
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2answers
74 views

Understanding a PNP switching circuit

Description I have the following diagram in which a switch connected to a 5V source should control two PNP transistors. I've spent a few hours trying to further understand PNP transistors to better ...
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5answers
434 views

pulsed current with 200 kHz squarewave signal

I use this circuit to obtain pulses as close as possible to the input signal pulses on the 1.5 Ohms resistor. The MOSFET is FPQ50N06 and the transistor is BC239. The circuit gives good results on 25 ...
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76 views

How to increase Amperage while keeping the Voltage the same

I currently have an Arduino Uno board which has an output of around 5V @ 900mA. is it possible to bump up the Amperage to around 3-4A while keeping the Voltage the same? Maybe with a Transistor, but i ...
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62 views

JFET circuit solving

I want to find out the value of R2, R3, R4, R5. How can I solve it? anyone can help me? For JFET1 VGS=0v, VDS = 15v. For JFET2 VGS=1v, VDS = 18v.
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Selecting suitable High Voltage / High Switching NPN transistor replacement for old PSU

I have an old Olivetti PC where the main input fuse in the PSU blows as soon as I flip the power switch (the same instant). Due to the specific form factor of this PSU I am thinking about trying to ...
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2answers
98 views

Applying heat to a transistor

I witnessed an experiment in which a transistor was connected to an led and a power supply. A lighter was used to heat up the transistor and this reduced the resistance of the circuit and made the ...
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1answer
59 views

Transistor operating point problem doesn't make sense?

Find the operating point of the transistors T1 and T2. I've been given this problem and when I try to apply Thevenin's theorem on resistors R2, R3 and then try to calculate \$I_{C1}\$, I get \$I_{C1} ...
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1answer
48 views

Does LTSpice even have a time delay for its MOSFETs?

When I use LTSpice to create a MOSFET, it comes with a very high resistance when closed and a very low resistance when open. My guess is that the creators of LTSpice just took two values that are some ...
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1answer
52 views

Why am I getting different behavior between my multiplexer and by bit storage schematic?

I had quite a bit of success using LTSpice to build a multiplexer with essentially two transistors. The example I'm attaching, "Mx4_Prob.asc", uses three MOSFETs, the two mentioned and one to amplify ...
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7answers
619 views

Emitter resistor and biasing voltage

In many articles regarding transistor biasing I see a circuit like below and I don't really get what is the point of biasing like this WITHOUT emitter resistor Re? When emitter branch is connected ...
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Bipolar Transistor Using Basis of Ebers moll Model [closed]

The general equations of the emitter and collector currents for the basic Ebers-Moll model [J. J. Ebers and J. L. Moll, “Large-Single Behavior of Junction Transistors, ” Proc. IRE., 42, 1761 (1954)] ...
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79 views

Is this circuit wired in parallel?

Sorry for the amateurish question. I am planning to tap into my car battery's reverse fuse to signal when it's time to receive a wireless signal from a rear-view camera. The camera-feed receiver in my ...
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1answer
478 views

Current mirror: is there a name for this NPN-PNP pair, and how does it work?

I'm looking at the schematic for the MC1460 voltage regulator. At the top it has three current mirrors, each with an NPN-PNP pair. Is there a name for that transistor structure? These pairs look like ...
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0answers
31 views

How to troubleshoot strange vce in a simple transistor circuit? [closed]

The attached diagram is the simplest setup that demonstrates my issue. Transistor is 2n3904. Attached pin of the Arduino is held LOW. I've been having issues with this circuit operating correctly ...
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1answer
104 views

Proving that the transistor in this simple schematic is off

I'm trying to find the collector, base and emitter currents of the transistor in the following simple topology: In order for the transistor to be on, the emitter needs to be at a higher potential ...
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0answers
69 views

Basic circuits to understand transistor [closed]

I am trying to understand how transistors work, and I'm having a difficult time finding some circuits to show a very basic way in which they work. For example, the following circuit helps me ...
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34 views

How would I apply miller theorem to the following capacitor?

So I have a common source amplifier and I am considering the high frequency small-signal gain of the circuit. I have derived the small signal model as follows where output voltage is taken at the ...
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2answers
112 views

Did I get this BJT configurations correct?

I'm trying to learn what kind of BJT transistors are this: Did I get them right?
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3answers
41 views

Question about Vbe and operation regions of BJT

Updated/Corrected question: Realizing what confuses me the most, I will make this more straight-forward. Say that a transistor works in the forward active region and it receives an ac input signal at ...
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1answer
39 views

What is the collector current of this transistor circuit?

Knowing that: $$V_{BE(on)}=0.7V, β=100, V_A=100V$$ I'd like to find the collector current of the following circuit: It seems I will have to use the fact that the base emitter voltage is 0.7 ...
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1answer
25 views

bjt reverse active currents

my question is on bipolar junction transistor, npn with 2 emitters, used in ttl nand gate. when in reverse active mode, and 2 emitter are in logic high, how is the collector current calculated ? since ...
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1answer
89 views

Transistor Circuit DC Analysis

I am struggling with solving this circuit. The current of drain is 1mA, and input impedance is 500k. and we should determine the value of R1 and R2. I don't know how to write its KVL using input ...
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1answer
43 views

Why is the following assumption valid? [duplicate]

For the following AB power amplifier VBB/2 is large enough such that both Qn and Qp are on for no input signal Vi, if output voltage is large and positive, it may be assumed that most $$i_{L} \approx ...
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1answer
102 views

Why is the minimum voltage not -Vcc?

So for the following circuit, the lowest the output voltage is -Vcc + Vce(sat) according to my textbook. However why can't we assume a lower value than Vce(sat) at the collector-emitter junction of Q2?...
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1answer
124 views

2n2222 can not make it work as gate

simulate this circuit – Schematic created using CircuitLab I am trying to make a simple switch with the 2N2222, so i can send 5 volts from a 3.3 V output pin on an arduino/raspberry pi. I have ...
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1answer
57 views

What IF amplifier configuration can I use in my receiver?

I am making a superhet SSB CW receiver with a crystal filter on the input after the mixer. Do I have to use IF transformers as the coupling method (1) or can I use capacitor coupling with resistors ...
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1answer
87 views

Transistor audio amplifier with dual voltage supply

There are lots of similar topics, but I can't find answer that will satisfy me. So, basically I am trying to do a transistor audio amplifier with dual voltage supply (+/-12V). I found circuit like ...
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4answers
203 views

Measuring voltage drop across a diode in a switched circuit

I have the below circuit where the input voltage is 8V and a PWM pulse is given to the base of the Q101 transistor. From what I have measured, The voltage at the anode of the diodes D102 and D103 ...
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1answer
50 views

Shopping for transistors question [closed]

I am trying to find a transistor that will allow up to 100 mA to pass through it while it is being saturated. I just don't know what value to look for. Any help is appreciated. Thanks.
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3answers
78 views

What does high impedance value mean?

I'm taking a look right now at page 215 of Verilog HDL: A Guide to Digital Design and Synthesis by Samir Palnitkar, where it's talking about Verilog primitives to represent MOSFETs. It says, "Thus, ...
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3answers
178 views

For the following amplifier, why is the output voltage 0 when input voltage is 0?

The amplifier is the following class AB amplifier: For an input voltage of 0V, the output voltage is 0V. However, I don't understand why. My textbook does not delve into why this is the case. (...
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1answer
47 views

Determine the drain current (PMOS-transistor)

I have the following problem: Consider the circuit below These component values are given: \$R_{G2}=1.5\text{M}\Omega\$, \$R_{G1}=1.2\text{M}\Omega\$, \$K=2.3\frac{\text{mA}}{\text{V}^2}\...
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1answer
28 views

CI HT12E enable control to reduce power consumption

So, following this datasheet (check out Application Circuit 4), I managed to transmit a signal and receive it on the other end. The thing now is: the whole circuit is drawing 2 mA, and that is because ...
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2answers
57 views

How is the ac load line for the following amplifier derived?

So I am trying to derive the ac load line for the following class A power amplifier First I considered the reflected load/equivalent resistance of the transformer, this becomes $$R'_{L} = (\frac{n_{...
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0answers
34 views

MOSFET calculations (Vds and Vds(on))

For a drain feedback bias E-MOSFET, (feedback resistance is very high), Vdd = 25V, Vgs(th) = 2V, Ids = 16mA and Vgs = 10V. If Vds(on) = 10V, what is Vgs and the value of the drain resistance R(d)? ...
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2answers
50 views

How can I use USB output (5V DC) to power a fan 12V DC load?

I would like to power a 5V DC/0.23A fan (beside another device such as 12V LED lamp, and 12V DC water pump). The only possible power source is using USB output, either from computer, mobile phone's ...
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0answers
40 views

what does bootstrapping mean? [duplicate]

I've recently encountered the bootstrapping term in a three stage amplifier circuit. Can you explain to me what does that technique do and mean? An expample would be great. Cheers
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3answers
100 views

Darlington as CB

Why do we use Darlington pair? I've heard that we don't use it as common base. Why is that? Why don't we just develop a BJT with high beta value istead of using this structure? What are the different ...
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3answers
115 views

What is the very basic electronic component to generate pulse wave (high or low) we commonly see in digital?

Very common we hear ON/OFF, HIGH/LOW, 1/0, or something similar in digital system. It is called binary. I would like to know what is the very basic component to generate such that binary system? I ...
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1answer
73 views

Semiconductor common emitter configuration

Please could anybody explain the CE configuration, the graphs of \$I_b\$ vs. \$V_{be}\$ and \$I_c\$ vs. \$V_{ce}\$. I can't understand which current remains fixed and how can one regulate \$V_{ce}\$ ...
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2answers
80 views

Why does amplifier power efficiency not consider the power input by the input signal?

If we are considering efficiency of a power amplifier, shouldn't I consider all sources of input and output power? Therefore, why doesn't efficiency consider the power of the input signal as follows: ...