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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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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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351 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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55 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
51 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
36 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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66 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
75 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
73 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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44 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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95 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
71 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
39 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
140 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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61 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 ...
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54 views

How to select a diode for baker clamp?

What are the requirements when selecting a diode for baker clamp circuit? 1- for example, How the reverse leaking current of the diode affects the circuit? can a diode with relatively high reverse ...
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1answer
77 views

Why can't certain isolated DC/DC converters operate at over 50% duty cycle?

I am currently studying two switch isolated DC/DC converters, more specifically the Push-Pull, the Half-Bridge and the Full-Bridge DC/DC converters. Several books say that these converters cannot ...
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1answer
38 views

Understanding CMOS Circuit Behaviour with Resistive Loads using Thevenin theorem

I have been reading the Digital Design: Principles and Practices 3rd Edition as a hobby. Unfortunately, I am stuck at page 103 of Section 3.5.2: Circuit Behavior with Resistive Loads. In Figure 3-27: ...
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114 views

Need Help With Transistor Logic Circuit Design

Greetings all and Happy New Year! I've been working on a logic circuit to control the main entrance gate at our ranch for some time now. I've been testing using Falstad's Circuit Simulator. ...
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1answer
40 views

Phase shift near saturation mitigation in input stage amplifier — How does this work, why does this work?

I'm trying to understand how this circuit works on the input stage to the 4192A Impedance Analyzer. Apologies for the quality... this is the best scan I could find. The design is furnished with the ...
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36 views

Acceleration of sequential computation over time

I am looking for a model (or "law", as in Moore's law) to describe the acceleration of sequential computation over time. By sequential computation I mean, for example, repeated applications of a hash ...
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1answer
135 views

555 Timer Stops working after a few seconds

I'm building a LED dimmer using a 555 timer (yeah, lame I know). I'm using it to produce photographic flat frames which require perfect illuminated fields even with shutter speeds as low as 1/1000 of ...
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2answers
104 views

DC current gain in complementary transistors

In Class-B amplifiers complementary PNP-NPN transistors are used, e.g. TIP2955 and TIP3055. https://www.electronics-tutorials.ws/transistor/tran_3.html says that They both have a DC current gain, ...
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Bipolar class-AB amplifier analysis questions

I am analyzing the following amplifier schematic Bipolar amplifier I'm wondering if their are any transistors that need to be cooled apart from the 4281A and 4302A output stage transistors? What is ...
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1answer
64 views

Why isn't my transistor outputting enough voltage when switched?

So, I'm a software guy, and this is a bit out of my element. I'm working with a Raspberry Pi, and I want to power one of an LED button, a push button with a pair of integrated green LEDs wired in ...
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2answers
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IC layouts - Transistors (Body)

I'm trying to get into IC layouts... Why do I see some IC layouts with or without the body terminal on the transistors. Do MOSFet transistors need a body terminal in an integrated circuit? Or should ...
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2answers
101 views

Cause of triode mode in MOSFET

My reference text introduces the MOFSET as follows: The text says the induced channel has uniform width as long as \$v_{DS}\$ is small, because in that case \$v_{GD} = v_{GS} - v_{DS} \approx v_{GS}\$...
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Measure the 'gain' of this circuit

I made this schematic using Ni multisim and I got asked to find the ‘gain of this circuit using a 1v p-p 1kHz sine signal’ and I was unsure about this because I’m not sure if it means voltage gain or ...
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21 views

Discrete solution for alternate zero (low) and one (high) at output? [duplicate]

I am trying to figure out a discrete solution for alternate low and high at the output for varying input. Consider the discrete solution as a block. Input to the system consist of a push-button. ...
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48 views

Off load voltage in npn transistor as a switch

There is transistor tutorial on sparkfun.com (https://learn.sparkfun.com/tutorials/transistors/all). I am wondering why there is 1.3 V drop depicted across the LED1 on the picture, since when the base ...
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1answer
59 views

led chaser with non-mechanical shut-off option

I've seen thousands of standard led chaser circuits online but I haven't seen one in which I can shut off all LED's in a non-mechanical way. I'm wiring one pin of my chaser up to a microcontroller so ...
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1answer
175 views

Level shiffter (3.3V / 5V) for controlling transistors

Is it possible to control the base of the transistor using the level shift chip (3.3V / 5V)? I want to use the SN74AHCT125 level shift chip. Transistor BC337-16
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How base and collector has nearly the same majority charge carrier concentration

Size: Collector > Emitter > Base Doping: Emitter > Base > Collector In the Function section of this Wikipedia page, they have said that Collector & Base have the same concentration of majority ...
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1answer
77 views

What is function of the resistor in series with bypass capacitor in npn transistor amplifier?

I am new to electronics and recently I was learning about npn transistor as an amplifier. I tried to build one in ltspice XVII. This is my circuit diagram: but the output was not as expected as ...
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1answer
408 views

Why is my transistor beta lower than expected?

I bought these transistors on digikey: BC549CTA Reading through the datasheet, (and on digikey's page), I am led to believe that the DC gain for this transistor is at minimum 420 [@ 2mA, 5V]. The ...
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1answer
89 views

Output current in collector of BC107

I am working on following circuit involving BC107 NPN Philips TO-92 transistor and voltage source of 4.2 V. simulate this circuit – Schematic created using CircuitLab I got some confusion when ...
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1answer
244 views

Led blinking with one NPN transistor [duplicate]

I am using scheme as shown below to blink an LED. But I'm using 9V battery source instead of 12V. I tried to use capacitors in range 100uF - 500uF to increase delay between blinks. Questions: ...
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2answers
76 views

Choosing a resistor for connecting a bipolar transistor

I need to run some LEDs using Arduino. The total current consumption is about 190 mA. For these purposes, I found a bipolar transistor PMBT2369 (Nexperia). Transistor characteristics: - Maximum ...
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2answers
107 views

Help with explanation on this transistor behaviour

Hi, I found the above circuit on a website where it was said to produce fade in effect for the LED's. I tested the circuit out in my breadboard with R2 as 1K and C1 as 1000uF and R3 as 100 ohms. ...
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1answer
41 views

Hybrid Model - Why differential of voltage equals AC component voltage?

In the derivation Hybrid Model (Equivalent Circuit) of transistor, there is a step that replace differential \$dV_1\$ with AC component \$v_1\$. However, to the best of my knowledge, voltage equals ...
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37 views

PLC Relay Output Circuit

Can someone help with this question? I've answered it to the best of my knowledge based on the learning materials provided but the answers I've gotten are exactly the same as the example. Should 5v be ...
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3answers
71 views

PNP and NPN transistor characteristics for this project (see link inside for schematic)

I'm working on this project https://github.com/diyhue/Devices/tree/master/HueDimmerSwitch I would ask which characteristics I need to keep in consideration to choose that two NPN and PNP ...
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1answer
121 views

Schmitt Trigger: Problems between theory and reality

I want to say that I am not a native English speaker so you may find some writing errors. Also, I am just learning electronics, so sorry if some questions are poorly formulated. I am trying to build ...
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35 views

Astable multivibrator

I found an Astable multivibrator schematic online and the transistor they used was a NPN 2n2222 and I didn't have one so I was just wondering if it's a must to use a specific NPN or PNP for ...
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1answer
75 views

How to calculate parameter K in mosfet

I know from the equation of Id that K = Id / ( Vgs - Vth ) ^ 2 but what Id if I don't have the value of Id? Should I use the value of Id on from the datasheet? ...
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33 views

Switch resistor with n-channel MOSFET not working

So I try to amplify a photodiode signal with an operational amplifier. As I want to amplify two signals (1 for a high-intensity light and 1 for a low-intensity light) I sort of need to design a ...
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65 views

Series BJT transistors with bases connected through a resistor

For an assignment I was given a problem which consists of two BJT transistors, a PNP and an NPN, in series with their bases tied together. simulate this circuit – Schematic created using ...
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29 views

Why is Ic constant in the plot of Vce vs Ic in a common emitter NPN transistor (in active region)?

In this plot, when \$V_{ce}\$ increases in the active region, shouldn't \$I_c\$ also increase as more electrons are getting diffused into the collector? Then, why is it that for a large range of \$V_{...
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42 views

Hybrid model of a transistor

Can someone help me to find the hybrid pi model of such transistor configuration? Assume Hfe = 90, the input voltage is applied in series with capacitor C2, (0.082uF) and Vout it from the red dot ...
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3answers
157 views

Why doesn't BD139 act as a switch like my 2N3904?

I got this low power transistor that I want to make a class-A amplifier out of, but I'm having a really hard time with it. It seems not to behave much like what I expect from a transistor. The ...
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2answers
56 views

Correct Voltage Detection

I have ran into a problem where some USB supplies drop below 4.6 volts. Is there a circuit that would block the voltage below 4.7 volts and pass the voltage when it is above 4.7 volts. I have tried ...