# 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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### Design a variable control motor [closed]

The following material are give 1 5vac 2. 20vdc electric motor 3. Variable resistor 4. Connecting lead 5. Led 6 IN4001 freewheeling diode 7. 1000pf capacitor 8. Transistors . with dis component ...
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### How to Charge Device With Phone and Charge Phone with Battery

I have a pretty unique problem (couldn't find answer on Google) for a DIY electronics project. I want to be able to charge a FPV Receiver via a phone and charge the phone with a battery. I want to ...
55 views

### Why does this PNP BJT use dual supply but the NPN not?

It's not immediately apparent to me as to why the following common-emitter configuration use two supply rails when used in conjunction with a PNP type BJT but the NPN version does not? To bias a BJT ...
33 views

### How is voltage split between load resistor and C -> E on transistor?

I am confused by the voltage reading in this simulation as VCE reads as 907V which means almost the entire voltage is dropped over the VCE at the transistor. I assumed that the VCE should be a fixed ...
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### How to calculate the tolerance of this constant current circuit?

I am using the circuit below to provide constant current to th LEDs. I request your suggestion on how to calculate the tolerance of current (minimum and maximum variation of set current) due to ...
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### Dependent vs. independent current paths

Taking the following circuit: The path on the left will be on and the same, whereas the path on the right is dependent on what is connected to the base of the transistor (not shown in the above ...
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### Diode Connected MOS

let's consider the equivalent circuit of a diode connected Mosfet. Since the current source between drain and source is: gm * Vgs = gm * Vds and it is proportional to Vds, it means that this ...
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### What happens to input character as $V_{CE}$ is increased?

In a NPN transistor and its study of input character, we obtain a graph (Ib vs Vbe) similar to that of PN junction diode. Now that is same for a same potential difference between Collector and ...
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### current mismatch PMOS (current mirror)

I am designing a PTAT (proportional-to-absolute-temperature) current generator with 2 PMOS transistors for a bandgap circuit. In which way does the aspect ratio of a MOS transistor (M1 and M2) ...
78 views

### Intuitive way to think of transistor saturation current?

I am having a hard time understanding what saturation current (denoted Is in my textbook) actually means for a transistor. For a diode, it makes perfect sense, it's the approximate maximum reverse ...
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### Amplifier transistors not receiving change in base voltage… do I look forwards or backwards?

So I'm working on diagnosing a CRT scope that isn't responding to the horizontal controls; the trace is off screen. The two X plates are each being driven by 2 transistors in line. One X plate has ...
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### Determining gain, KCL/KWL (Basics)

Below is a pi model schematic of a cascaded amplifier. The goal is to find the gain with Rp as load. So the gain would be: $A = \frac{V_{out}}{V_{in}}$. So i set out to find $V_{out}$ in terms ...
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### When does I_C be approximately equal to I_E

I have seen in certain problems, they say that $$I_E = I_C$$ by saying that β is very large. I don't understand what can be considered as large β. So, I want to know the range of the values ...
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### Gain bandwidth product for amplifier

If a question simply asked "What is the gain bandwidth product of this amplifier?" And when I am trying to utilize the equation : GBW = (Av)(BW) I am unsure if I should utilize the voltage gain ...
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### What purpose are the transistors serving in this CRT oscilloscope circuit?

So this is part of a CRT oscilloscope diagram, and I don't understand the function of the transistors on the bottom right, Q18 and Q19. Their outputs (41 and 42, crossing through the dotted line) go ...
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### How to turn on a 12V Buzzer when transistor is OFF in the given circuit using minimal components?

In the given circuit i need to add an alarm circuitry where the 12V buzzer is ON when relay/transistor is OFF. Please guide me how to connect the 12V buzzer with minimal additional components
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### What is this circuit's purpose

The input is a current source (photomultiplier), and the output is connected to a charge amplifier (I belive). I tried to draw the schematics from the circuit board, but I don't know what the three-...
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### Plotting impedance of an inductor and capacitor in series

The capacitor and inductor are in series, which means that the equivalent impedance of these two elements is $$Z_{LC}=\frac{1-\omega^2LC}{j\omega L}$$ So for the three cases I got the following ...
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### Leads of a particular electrical component

Is lead the most common term used in electronics to indicate the number of connectible input/outputs that a component has? Are there other terms that are used ...
98 views

### PNP transistor switching and inductive load

I am designing a circuit to control a motorcycle horn (its operating frequency is 490 Hz, its resistance is 3 Ohm, and it consumes 1A on average as indicated by the power supply), and LED lights. The ...
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### Problem in understanding transistor

I am high school student we are doing transistor in our class but I could'n understand the topic, I have read several answer on site both physics as well as electrical engineering stack exchange ...
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### Draw the maginitude as function of frequency

The circuit is this one, it consists of two common emitter transistors simulate this circuit – Schematic created using CircuitLab Some of the components where given but the others I had to ...
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### Finding the component value of PNP transistor

This is my circuit simulate this circuit – Schematic created using CircuitLab This is the way I tackled this problem:  U_{e2} = 12 - I_e \cdot R_e = 12 - (2.02 \cdot 2) = 7.96 \text{ V} ...
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### Why does this BJT work as a switch in this logical-NOT circuit, no matter how I orient the emitter and collector?

I have built the following circuit (obtained from Electronics All-in-One For Dummies (For Dummies 2nd Edition)) It works quite well. When the the momentary button (normally open) is not pushed the ...
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### How to properly implement a crowbar circuit to perform a fault injection / power glitch attack?

I am trying to implement a power glitch attack. This is a hardware attack in which for a very short period of time (order of nanoseconds) I remove the power to a processor, using a transistor, to ...
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### Working principle of a MOSFET Transistor

I was just reading a blog entry regarding the power conflict of the Arduino and trying to understand everything, when I came to a point where I could not understand the working principle of the ...
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### What could be the reason that this transistor gets too hot unexpectedly?

In the following circuit, for the transistor it can be calculated that: Vce=4.5V and Ic=170mA. I also implemented this on breadboard and measured almost the same quantities. The opamp is an LM324 and ...
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### Calculate the potential and current in the transistor circuit

I'm stuck on a question where I need to calculate the potential Vx and the current Ix in the circuit below. I have managed to get some equations, but the question does not mention what the ...
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### How to calculate Resistor needed in PNP Transistor Circuit

I am trying to calculate the resistor value I need to achieve 35mA in my circuit. Vcc is 5V. Can someone explain the values I need to find in the datasheet as well as formula to use to find the ...
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### Finding and plotting the impedance

I have gotten some help from the community here and thus I have reached this. This is part of the circuit that I want to find the impedance simulate this circuit – Schematic created using ...
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### relay switching troubles

I am trying to switch a pair of 12v relays with approx 750r coils using a circuit and pre-fabricated pcb that I was given. The idea is that one relay is on when the other is off. The control comes ...
44 views

### Buffer amplifier for DC-1MHz (discrete parts)

I would like to make a buffer amplifier from discrete parts (transistors) which is working from DC to 1MHz. I'm not able to google any schematic or tutorial or app note etc. Everything I found was ...
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### LED Strip / Resistor Heater + Driver Circuit

For my astrophotography equipment, I need to construct a dew heater and a flat field generator. A dew heater is simply a bunch of resistors connected in parallel such that each resistor outputs about ...
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### Why do NPN/PNP transistors need to use doped semiconductors for the 'N' region?

By my understanding, as long as the P layers are properly doped (to have fewer free electrons), the electrons could not flow between collector and emitter until the P is given a satisfactory level of ...
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### Why we need two resistors to control the gate voltage of a PUT transistor?

Looking the follow schematics you can see two resistors 15k and 27k that are controlling the gate voltage of the PUT (programmable unijunction transistor) transistor. My question is why we need two ...
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### Of the millions of transistors in a typical microprocessor, what percentage of them are BJTs and MOFSETS?

This is broad in the sense of which microprocessor I am referring to. I expect them to be similar, but if not, then how about in an Intel 7th gen CPU and in an A11 iPhone chip? And what about how ...
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### How the capacitor charges in this circuit?

I have been working on a kind of edge detector, and I would like to be guided about how the capacitor will charge in this circuit. when I don't have any transistor I could easily calculate the ...
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### Transfer Function of two Common Emitters

I'm sorry about the pictures and used circuitlab. I am dealing with a circuit that has two common emitter transistors. Until now I was only dealing with a circuit that that is common emitter. This ...
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### Transistor for 5V relay

Following up this question I need a transistor to switch the necessary current through the coil. I have some spare BC817 lying. My digital output pins can switch 5V@20mA. Do I need a base resistor to ...
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### the transconductance of cascade MOSFET IF channel length modulation is NOT ZERO

What would the derivation of the cascode MOSFET transconductance in small signal analysis IF THE CHANNEL LENGTH MODULATION IS NOT ZERO, as most examples for the cascode mosfet transconductance say in ...
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### PNP Highside Switch For Capacitive Sensor

Am wanting to use this Capacitive push button for a project but am having trouble understanding the application circuit. I understand that it is a PNP Highside switch and that current will flow to ...
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### Reading recommendations to better understand how to understand the intended function of a circuit

This is a general question. Suppose I have a circuit like below from CircuitDigest: ￼ My supervisor said that about the circuit that.. [The] circuit does actually involve an amplifier, even ...
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### Starting on electronics from zero - transistor timer

I'm just starting on electronics, trying to build a few circuits but can't understand properly how things work. I got this circuit and put on a breadboard, but the power source I have is 5V instead ...
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### How to project a FET transistor as an amplifier?

I am trying to solve a problem on using an FET transistor as an amplifier with the common source configuration. The model should be appropriate for high frequencies. The problem gives the equivalent ...
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### Transistor is not switching-Raindrop sensor with LED (Later Buzzer will be used)

I am creating a small application in which on detecting the water the Buzzer will ring. But right now I am testing with LED instead of Buzzer. Raindrop Sensor datasheet link: https://components101....
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### Find DC components of npn and pnp transistor

I'm sorry but I can't seem to figure this transistor question. The question goes as follows: Draw a DC-circuit and determine the unknown component values. Which DC-voltages ( reference is ground) ...
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### Role of input resistance in LM384 Audio Power Amplifier

let's consider the LM384 Audio Power Amplifier (here the datasheet) Can you explain me why is there the 150k resistance? It lowers the device input impedance, which is not good for a voltage ...
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### How do we create current sources?

Constant current sources (simply, current sources) are useful and necessary devices. They are widely used to drive LEDs, charge capacitors and batteries, to bias differential amplifiers, etc. The only ...