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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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PNP Transistor with low base current

I designed a PCB with the following schematics. simulate this circuit – Schematic created using CircuitLab The circuit uses a MAX6369 external watchdog timer which has an open-drain output(...
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1answer
32 views

How does this high impedance circuit stage work

The current i1 flows through Q3 and current i2 flows through Q4. It looks like D5 is trying to mirror the current flowing through it via Q6. D6 is trying to mirror the current flowing through it in Q5....
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1answer
255 views

Why are the input and the battery connected in a transistor amp?

I'm trying to make a simple boost pedal for my guitar using the simplest schematic I found. I'm wondering why the input is connected to the +9v battery in this schematic through a 430kohm resistance. ...
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33 views

4-20mA current loop - transmit sensor reading

I am working on design loop current transmitter- to transmit reading value from thermocouple sensor using below design. I measured co-junction temperature using NTC instead of RTD. During applying ...
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3answers
69 views

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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0answers
66 views

Where should I put the transistor [on hold]

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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3answers
64 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
45 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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38 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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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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71 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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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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1answer
719 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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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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1answer
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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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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1answer
33 views

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

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
81 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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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
185 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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69 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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4answers
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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
35 views

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
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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4answers
190 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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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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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
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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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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0answers
27 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
36 views

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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1answer
68 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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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
63 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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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
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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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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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? [closed]

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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63 views

Transistor switch help

I am a total beginner on electronics (I bought my first breadboard very recently) and I have a question that I can’t seem to find the answer on the internet: how can I make a pnp transistor switch on ...
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2answers
66 views

MOSFET as Power Switch Issues

I am trying to use a N-channel MOSFET to toggle battery power going to a 5V voltage booster using the circuit shown in the attached image. Battery voltage is 3.7V and the gate voltage is 3.3V. High ...
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1answer
71 views

Is my pin understanding correct on the 2N3904?

I have the following in my circuit: Am I right in understanding that the pins top to bottom are: 1/Emitter 2/Base 3/Collector where the top square pin is Emitter, middle pin with red trace is the ...
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0answers
42 views

BJT: Is \$ R_E || [\frac{R_s'}{\beta}+r_e] = (R_s'+ \beta r_e)|| \beta R_E\$?

I am trying to find the effect of \$ C_E \$ on voltage gain. Circuit under AC conditions: Doubt: Is \$ R_E || [\frac{R_s'}{\beta}+r_e] = (R_s'+ \beta r_e)|| \beta R_E\$ ? Reasoning: Small ...
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0answers
69 views

CCD output buffer

Reading the KAF-8300 CCD datasheet, I came across what looks like an emitter-follower to buffer the analog video output, see below: Also from the datasheet: Charge presented to the floating ...
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1answer
63 views

Is there a variable forward voltage diode-like device or circuit construction?

I need to make a test PCB for an LED drive circuit that can drive a variety of different single LEDs. The forward voltage (Vf) of the LED could be anywhere from ~2.2V up to ~6.5V. I'd like the test ...
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1answer
35 views

GPIO of ESP8266 without base resistance

I know that the maximum output current of a GPIO of the ESP8266 is 12 ma I have seen the next circuit and I have done it, it works perfectly, I have measured the base current and it gives 10 ma My ...
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2answers
110 views

Transistor circuit driving me insane

Consider the following circuit: Now I'm asking to impose the base current as zero and $$R_C=452.35 \Omega $$ Now I have a lot of issues with this circuit because I can't find a systematic way to ...
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2answers
37 views

Alpha and Beta of a Transistor

So the parameter beta for a Common Emitter Amplifier is called the Current Gain and is defined as \$\beta =\dfrac{I_{collector}}{I_{Base}}\$ \$\alpha =\dfrac{I_{collector}}{I_{Emitter}}\$ What is ...