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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 to use a transistor to drive strings of LEDs from GPIO pins?

This is similar to How to drive a 20mA LED From a 4mA max GPIO Pin except that I need a little more hand-holding in order to understand what is happening. For background, I'm a software engineer and ...
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59 views

Where should I put the transistor

I have written a digital input program for an Arduino to turn on an led for 12.5 seconds. But, the light I have needs 110 V and I am using a 9v battery. I was told to use a transistor. If you can ...
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61 views

Selecting a transistor - Reading transistor datasheets

I am trying to select a transistor part and figure the actual current calculations in my circuit. I have 30mA of collector (load current). This is the transistor I am choosing for my design : https://...
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1answer
26 views

Speed of monostable circuit

i need to find a time between rising edge of input signal and generating new output state. I dont have a scope so i cant measure Does someone have imagine how fast it is and how the edges looks like?
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41 views

Push Pull Switch Mode Power Supplies

I am reading this material for understanding the switch mode push pull power supplies. Push Pull Switched Mode Power Supplies I am unable to understand the working though. Can someone provide a ...
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0answers
31 views

Understanding Optimization/Realization of the voltage controlled current source

I am unable to make a voltage controlled constant current source. So I am using the following scheme (Sorry for bad sketch drawing): The constant control voltage varies in the range of 0 to 5 V is ...
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94 views

Power amplifier, does this circuit work?

I found that circuit for a power amplifier. Does it work? I want to build one for myself.
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152 views

Arduino - Using NPN transistor as a switch to pull-up/down analog pin

Let me start by saying that I am not an EE, and my knowledge in Electronics is basic, so please bear with me and be patient if, initially I am bending a few rules. In Epee fencing, a touch is awarded ...
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1answer
716 views

What is this substance on board?

So I’m trying to fix my blu-ray player and there are two spots where this beige stuff is. Is this there intentionally, or is this the result of some malfunction? Could someone please explain what it ...
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70 views

Stumped about how this switching circuits system works

I have stumbled upon this circuit from an online electronics course (https://pirateselectronics.teachable.com, chapter "Dual Flash Lights"): The behavior of this system is that both LEDs switch on ...
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4answers
188 views

Constant current source gets heated

I am trying to control some power LEDs using a microcontroller. For this I plan to use a transistor based constant current source to protect the LEDs from getting damaged and PWM on the base of the ...
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3answers
52 views

BJT Active mode - How does it work

I am finding it difficult to understand how exactly this works and would appreciate any help. From my understanding: The emitter base junction has to be in forward bias meaning that Vb is more ...
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46 views

Op Amp Output Voltage

I have a question about an LM741 op amp IC. I am using the op amp as an comparator (open loop with no feedback), as seen below: When the op amp output is low, the output voltage is still around 1.2v....
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41 views

Controllable power source (current) with one transistor and one resistor

I have this circuit: It should be a controllable powers source for current. Is that right? 1) What's the name of this circuit? 2) What does the resistor and how can I calculate it? Thank you!
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176 views

Common collector transistor

According to my understanding the common collector transistor should be like figure-1 but in book it is given as figure-2 and in it Vcc is given.Can anyone provide me proper explanation of this.
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1answer
46 views

Why is one of the transistors in ROM sense amplifier twice the width of the one opposite of him?

The picture is of Sense Amp design of ROM component in which a 'dummy' bit line is used to imitate the current so that the proper information can be derived from the memory cell by comparing the ...
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2answers
80 views

Unable to activate an Nmosfet gate with raspberry pi

So I've been trying to control a motor using a MOSFET transistor, where the gate is controlled by a raspberry pi. My circuit is wired as follow: The diodes represent the raspberry pi ground and gpio ...
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1answer
176 views

peltier driver using AMP OP and MOSFET

i'm in trouble trying to figure it out how to properly control a peltier cell using current control principle . I'm using a sine wave to figure circuit behavior through 0 to 6V and 0.5HZ . Take a ...
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1answer
32 views

What should be values of resistors and voltage sources in common emitter configuration of transistor for it to act as an amplifier? [on hold]

Here i took some random values So please suggest me values for the resistors as well as the for the voltage sources for transistor to act as amplifer
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2answers
166 views

Transistor Power Dissipation / Overheating

I am working on an audio project in which a voltage controlled square wave oscillator drives a 5W 4Ohm Speaker. I am using a unipolar 12V supply. In order to limit the current going through the ...
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4answers
99 views

Circuit to convert 24VAC digital signal to 5V DC digital signal

I am designing a circuit to convert 24VAC signal to 5V DC signal. The 24VAC signal is designed where 24VAC is on and 0VAC is off. The signal needs to be fed to an MCU which is 5V DC. The circuit ...
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2answers
49 views

Is this a suitable Voltage Regulator to replace an old circuit on my board and is my logic correct?

I have 4 of these 2n3904 transistor setups on my board: A1 -- requires 5v on these 2 connected pins to be enabled. I control this by driving r2 high at 3.3v which should allow 5v to flow through the ...
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1answer
184 views

Mystery component in Selfie Stick? (iPhone)

What is the component inside an iPhone selfie stick? Testing reveals it is not a transistor. We have done some probing of it and come up with the following: The mystery 3-pinned component drops the ...
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1answer
91 views

Finding current through an LED in an amplifier using a BJT

Suppose you have the schematic: My job is to find \$I_{LED} \$ knowing that the impedance of the capacitor in negligible against \$V_s\$. Here's my attempt: I intend to do an AC analysis followed by ...
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68 views

Darlington Transistor TIP142 same type but different values

I have a bunch of Darlington NPN Transistors TIP142 that are removed from two separate identical boards. The 1st one have the TO−218 CASE (left side of the image) and the 2nd the TO−247 CASE (right ...
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2answers
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Can I in any way connect +ve side of my led to uln2083a output pin?If no can I do it with M54562 transistor array?

I had conneced my digital pin of arduino to the uln2803a to drive LED. I want to configure my uln2803a such that i can connect +ve side of the led to the output pin of uln2803a IC.
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1answer
164 views

Using a single power source for both the gate and source of my transistor?

I am using an IRFZ44N MOSFET (n-type) transistor to regulate the current of a Lithium-ion battery, and I'm trying to use the battery to supply power to both the drain and gate of the transistor. My ...
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5answers
4k views

Transistor which opens circuit, reverse transistor

I'm wondering if there is a transistor which, when a voltage is applied to the base / gate, opens the circuit instead of closing it. If there is not, how would such a configuration be created? EDIT: ...
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2answers
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How do I connect a relay and transistor to an Arduino? [closed]

Ok, so this is what my relay looks like. I can't figure out what pins I hook the arduino and transistor to, and what pins to hook the the other device. Please help.
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1answer
172 views

How can I correct instability in a push-pull transistor amplifier?

In our EE lab, we had to build the following amplifier. It is from this lab manual, page 40. A week ago, I built it successfully, with 2n3904/3906 and d44vh10/ d45vh10 for the power amplifiers (Q3,...
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1answer
66 views

In an NPN transistor, why doesn't current flow without applying a base voltage?

In an NPN transistor, why isn't a typical C-E voltage sufficient to overcome the internal resistance of NPN junction directly? Since we only need 0.7V to overcome the PN junction from the Base to ...
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1answer
39 views

Controlling the power supply of a bluetooth module via GPIO and a transistor

I want to be able to turn a Bluetooth module on and off via a GPIO pin of a microcontroller. My first approach to realize this with a transistor is shown below. Is this approach correct? If not, how ...
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3answers
100 views

How to define a microcontroller pin as open collector or open drain?

Source I have understood the fundamental theory of open collector and open drain configuration. But the problem is how to define/make a micro controller's pin as open drain? Can any pin of a micro ...
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2answers
72 views

Better Transistor Inverter Using Ground Signal?

I'm getting close to finishing my brand spanking new gate control design. I sincerely appreciate all the help I've received out here. My latest challenge is to extinguish an LED when a circuit is ...
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1answer
63 views

Pausing a clock signal generated by 555 timer

I am planning to make a simple integer adder/multiplier which needs a variable frequency, comparatively slow clock (around 1 to 200 Hz) for demonstration purposes. I used the following generic 555 ...
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1answer
41 views

Unity Gain Phase Splitter- Why outputs have different voltages

I’m trying to calculate the values of the biasing resistors for this phase splitter circuit. (I know the actual values of the resistors, but I just wanted to manually work it out). When I made the ...
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2answers
63 views

H Bridge extreme voltage drop

I was trying to implement a H-Bridge circuit but had a lot of failures. I'm not really good with electronics, just some basic knowledge. So I've started by creating an buffer to switch the full ...
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1answer
67 views

Common collector - bias resistor?

[Original question: CCD output buffer; seemed best to make the transistor part a separate post] Taken from Wikipedia, the circuit in Fig. 1 acts as a common collector (high input impedance - low ...
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4answers
346 views

Gain in current but not in voltage -transistor “voltage follower” set up

Suppose we have the circuit set up as shown in the image. Also suppose that $$V_s=\overline{V_s}+v_S$$, where the smal v is for the variable component of the signal which varies much faster than the ...
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2answers
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Logic Circuit Transistor Resistor Values?

Last week, I posted a problem with a logic circuit (Need Help With Transistor Logic Circuit Design), and Analogkid was kind enough to solve it. However, at the time, I didn't realize I still had a ...
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0answers
26 views

Dimensioning a “NOT” gate with a bipolar NPN transistor

With the schematic below I am to determine a "NOT" gate the value of Rb to which the circuit acts as such, knowing that the voltages given for the logic levels are: $$0\to V\in[-0.3,0.9]$$ $$1\to V\in[...
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2answers
61 views

What is the turn-on and turn-off condition of the npn-transistor?

Following is the circuit I have been analyzing. My intention is to calculate the turn on and off condition of the transistor Q1. R1 and R2 (10 kΩ each) are internal to the transistor. simulate this ...
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416 views

Thevenin equivalent for a transistor circuit

I'm having trouble with this circuit and was wondering if someone could help me. So far I know that the 20V source can be basically ignored since it is a NPN transistor here. The second circuit here ...
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2answers
48 views

Select between two sources with transistors

I'm sorry if this has been asked before but I can't find useful data on this matter. I have two sources of data and I want to select one of them using transistors. If I had to guess I'd make the ...
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2answers
855 views

KVL and KCL in MOSFET small-signal model, how?

I want to find the gain in this MOSFET small-signal model. KVL in loop 1: \$+V_{in}-V_{gs}-g_mV_{gs}R_s=0 \iff V_{in}=V_{gs}(1+g_mR_s)\$ KVL in loop 2: \$+V_{out}-g_mV_{gs}R_s=0 \iff V_{out}=g_mV_{...
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2answers
52 views

IR receiver giving constant current

simulate this circuit – Schematic created using CircuitLab This is a circuit I made with an 1838D IR receiver in order to test if a tv remote is working, but as soon as I press the button, the ...
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1answer
705 views

Designing a VHF Colpitts oscillator using BJT

I am trying to design an Oscillator circuit which can produce a good sine wave with a frequency of at least 500 Mhz and oscillating voltage of around 10 - 15 volts. The output of this oscillator will ...
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1answer
33 views

Voltage Circuit Switch with BJT

I have Found One Circuit Which acts as Switch to Pass 15NV (15 Negative Voltage) to Opamps Negative (-VCC) Supply But I am unable to understand its working . Why Two NPN are used in this Circuit ? ...
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Best 2n2222a based audio amp schematic for piezo buzzer disk contact microphone for human speech? [on hold]

Could anyone point me to a good, or even awesome circuit schematic using the 2n2222a transistor in an audio amp for a piezo buzzer disk contact microphone? I intend to use it to capture and listen to ...
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1answer
770 views

Can I create a CMOS AND gate with 2 serial n-type and 2 paralel p-type CMOS transistors?

So I know that a CMOS AND gate is made with 2 parallel p-type transistors and 2 serial n-type transistors and an inverter on the output. But can we just make the AND gate similar to the NOR gate -...