A type of bipolar transistor comprised of n-type semiconductor in contact with p-type semiconductor which in turn is in contact with a n-type semiconductor -> thus NPN. The transistor has three terminals, the Emitter, Base and the Collector. Current injected into the base controls the flow of ...

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NPN Transistor Noninverting Amplifier

I know how to design an inverting amlifier with a NPN transistor. Now I need to make a electret microphone amplifier to connect with Arduino, which only reads positive voltage values. Is there a ...
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1answer
80 views

If the depletion layer of a transistor collector/base junction is thick, why are majority carriers still collected?

In "Principles of transistor circuits, 8th edition" (top of p26) it is said that once holes have been injected in the base region by a forward biased base-emitter junction (which I understand) of a ...
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4answers
81 views

Transistor biasing problem

Suppose this is the biasing process of an NPN transistor. simulate this circuit – Schematic created using CircuitLab The battery to the left forward biases the emitter diode because its ...
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2answers
83 views

How to choose a transistor for amplification

I've been trying to find information on choosing an NPN transistor but everything I've found seems to apply to saturated transistors only. I'm basically trying to amplify the current given from a 3mm ...
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3answers
166 views

Control voltage using transistor

I know nothing about transistors except they can be used as simple amplifiers. I do not know which one to use for my project. A port from arduino would give me volts ranging 0V-5V. I have an external ...
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3answers
302 views

Why shouldn't you use the emitter of a BJT NPN Transistor as a current source?

Several times here on the EE Stack Exchange, I've seen people say not to connect a load between the emitter of an NPN transistor and ground, but instead connect it between the power source and the ...
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44 views

High base-emitter voltage NPN transistor

I just bought some NPN transistors for my project. I didn't notice before buying them, that the specification said the transistor had a emitter base voltage \$V_{be}\$ of 9 volts. Can this be true? ...
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1answer
125 views

Switching power between two 7-segment displays using NPN transistors

So, I am working on a small project and forgot to order PNP transistors to switch the power to two common-anode 7-segment displays. Like this, for example: All I have in hand at the moment is a ...
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3answers
151 views

Transistor saturates no matter the size of base resistor

Problem I have a circuit as depicted below, and after calculating the base resistor, I wanted to see when the base current would be too little to saturate the transistor. I kept increasing the ...
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2answers
53 views

Potentiometer after NPN transistors

I was looking to use a potentiometer to limit brightness for LED matrix. The problem I ran into is I would need a lot of potentiometers. The Led matrix will be multiplexing so only one Led will be on ...
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1answer
131 views

Why won't a switching transistor work in this circuit

I've been working with an Arduino lately, and building various breadboard circuits. A simple example was to build a transistor based inverter for a project involving 9600 baud serial combination at ...
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2answers
294 views

How to replace this NPN transistor with a MOSFET?

Here is the schematic of the circuit I'm trying to build (source) but I only have an IRF9530N Mosfet; I don't have any NPN transistors at hand. What would the schematic look like with a MOSFET ...
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80 views

How does mosfet allow current to flow at the Pinch off mode?

I understand the mosfet other than in the pinch off mode? If the Inversion layer pinches off, how does it still allow the current to flow? Look at the bottom two images.
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5answers
166 views

H-Bridge out of 2 (1 PNP, 1 NPN) Darlington Arrays

I need to control, with a µC, 4 single-coil latching relays and I am exploring various options. My first bet would be a H-Bridge. Since H-bridge ICs are quite expensive and are mostly designed to ...
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1answer
107 views

Simple NPN circuit

I'm stuck on the start on my school project. I need to design and build this circuit. Transistor parameters: Ic = 0,5A, Uce0 = 80V, Ucb0 = 80V, Pd = 0,625W, h21E = 100, LED Diode parameters: Uf ...
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2answers
134 views

Problem with NPN transistor in MOSFET circuit

simulate this circuit – Schematic created using CircuitLab Gentlefolk, I am attempting to build a circuit to switch power through a P-CHANNEL MOSFET device. I believe I am on the right ...
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3answers
96 views

Trouble driving NPN into saturation [duplicate]

I can't saturate my NPN transistor! Here is my circuit: simulate this circuit – Schematic created using CircuitLab The Vce is around 1.7 V, which is way above the saturation Vce of 0.3, ...
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4answers
204 views

Turn on a 7812 Voltage regulator using an Arduino?

I'm using an Arduino in a project, but this is not an Arduino question! I'm able to switch 5+ volt high or low using a digital write pin. I need to use a 7812 voltage regulator to regulate voltage ...
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2answers
263 views

How to calculate the required base resistor for this BJT-relay circuit?

I'm trying to design a relay circuit for my first PCB and have come up with the following: The 10K value for R7 is just a placeholder. R7 is what I'm trying to determine. The transistor should ...
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1answer
135 views

Issue with driving multiple LEDs via transistors

I am attempting to individual control multiple LED-based light sources via PWM. Now I am somewhat familiar with transistors and their usage, and had no issue setting up one instance of this control ...
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2answers
2k views

Why are two transistors often used instead of one?

Many circuit designs I see with transistors use two transistors chained together instead of just using one transistor. Case in point: This circuit is designed to allow a device with a 3.3V UART to ...
2
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1answer
471 views

2N2222A Mismatch between emitter and collector

I am trying to figure out what is going on here. I have a simple circuit to send current to a brushless fan running at 12V on the high side, using a NPN transistor 2N2222A: This is the picture of ...
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1answer
141 views

L298 high side driver: how does this actually work?

I recently took another look at the L298 since some students were having problems (due to the commonly discussed high V_CE-on of the combined high side and low side drivers). One thing that struck me ...
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1answer
107 views

Newbie Question about NPN amplifier circuit

this is my first post here. I’ll just dive in and hopefully learn something. I’m relatively new to electronics, and getting to grips with the terminology etc. Please correct me if I am describing ...
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2answers
165 views

Driving a transistor base with PWM

I'm in desperate need of help here! No matter what I try, I can't seem to get this working! I'm trying to drive a signal transistor with PWM on an AVR ATmega32. My PWM signal looks as it's supposed ...
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3answers
404 views

NPN BJT Relay Circuit will not turn off

I'm applying a 3.3V signal with my Raspberry Pi to the base of an NPN transistor to activate a SPDT 6V relay (relay data sheet, model G2R-1-S-DC6(S)). The relay pickup/dropoff voltage is 4.4/0.9V. ...
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3answers
847 views

What determines how much current can flow through a 2N2222 A?

I've been fiddling around with a brushed DC motor, a 2N2222 and an arduino's PWM to get different speeds out of my motor. Now, based on a video tutorial I watched on youtube, It was recommended to put ...
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0answers
96 views

How to get better output out of flyback driver?

simulate this circuit – Schematic created using CircuitLab I used this circuit to power my flyback... I used an MJE3055T Power NPN and 10kOhm pot. The flyback is FKD15A001. I used the ...
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2answers
750 views

Simple electrical circuit won't work

Simple NPN switching circuit to open a relay circuit, first NPN switching part didn't want to work (3rd PCB and endless times of trying). Circuit wizard diagrams, I split its first part to figure out ...
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1answer
192 views

Why does my NPN circuit only work with a separate power supply?

I'm trying to use an NPN transistor to switch a power supply with a proprietary connector on and off. I can get the supply to turn on by shorting two of the pins. In stand by one of these pins ...
3
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2answers
1k views

Control 5V DC motor with Arduino

I'm trying to build a circuit to control a 5V DC motor with Arduino. My issue is that I can't understand the resistance value within this scheme: Which resistor should I use in order to make work ...
4
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1answer
598 views

Protecting NPN transistor from negative base-emitter voltage?

I have a circuit that converts 5V RS-232 polarity signals (logical 0 = +5V, logical 1 = -5V) to 3.3V TTL polarity (logical 1 = 3.3V, logical 0 = 0V) using a BC548 transistor. It forms a NOT gate so ...
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2answers
314 views

Using a PNP instead of an NPN in a circuit

The figure shows my circuit. The transistor I am currently using is a MJH6287 (PNP) as opposed to whats shown in the figure (MJH6284 - NPN) The circuit with the PNP transistor worked just once ...
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2answers
299 views

Driving 3 LEDs at 1000mA. Is this circuit / driver ok?

I want to drive 3 LEDs in Series at constant current of approx 900mA - 1000mA. Will this circuit work? The LEDs are Vf 3.55V @ 1000mA. LED Diagram R1 = 0.25W 100k Ohm Resistor R2 = 2W 0.47 Ohm ...
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4answers
536 views

How to use a NPN-Transistor to get status LEDs for an ATX power supply?

There are many instructions "How to Convert a Computer ATX Power Supply to a Lab Power Supply". Often they suggest they suggest to place to staus LEDs to indicate it the power supply is turned on or ...
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2answers
243 views

Help with bipolar LED's and Transistors

Let me first say I'm new to electronics. :) So, my question is will this circuit work? I'm trying to light up a 2 lead bipolar LED using 2 pins on a microcontroller. My theory is when the mcu pin 1 ...
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2answers
255 views

Good NPN configuration vs bad configuration

Let me try this post to see if I can properly ask the question. I have the common emitter configuration which works for me, the math (Ie = Ic + Ib) works. The load is in series to the collector. And ...
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4answers
867 views

NPN Transistor in common collector configuration, Vout varies

I am trying to make a power supply which gives a constant 5V at output with a current limit of 1 Amps. I am using D1047 NPN transistor in common collector configuration, with 5V (low current) voltage ...
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2answers
243 views

Which resistor for NPN transistor base?

Which is the way to choose a resistor for a NPN transistor base? I want to use P2N2222A as a switch, in a design as shown below. When I have voltage in base (1.8 V), I want a connection to be created ...
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1answer
1k views

Applying hybrid-pi model of an npn-BJT to a pnp BJT in small signal analysis

When doing the small signal analysis of a circuit containing a pnp BJT connected to either the emitter or collector (or base?) of a npn BJT, is it possible to apply the hybrid-pi model for the npn-BJT ...
2
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1answer
261 views

Amplified 80dBA 40KHz Sound From 3V Square Wave?

How can a loud high-frequency tone be produced from a 3V square wave? Given that: the square wave is 3V and can have a varying frequency (max 4mA) 12VDC high-current supply is available ...
4
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2answers
339 views

Problem modelling NPN transistor BE junction in LTSpice

So, I am trying to understand transistors. I start with the very basics, the part which says that an NPN transistor kinda look like two diodes joined at the hip (at the anode, in fact) I build the ...
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2answers
317 views

Equivalent inductance of this gyrator

According to this link, the following schematic is equivalent to an inductance R1*R2*C placed between input and ground. Under which conditions is this true? As a guideline, we assume Vcc=9V. See this ...
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3answers
510 views

Transistor as switch

In the last few days I spent working with NPN transistors and measuring their characteristics. My aim was measure VBE and IE when transistor will turn on (transistor as switch). For all tests VCE = ...
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1answer
206 views

what's the purpose of this transistor setup (answer: simulate an inductance)

I encounter the following block in three regions of an Altec Lansing APT3 2.1 speaker system. simulate this circuit – Schematic created using CircuitLab Given that VH = 9V D.C., I only ...
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1answer
229 views

Difference between power on Arduino Pin 13 and Other Digital Pins

I am using Arduino Digital Pins to turn on and off a relay. Now I am using the 5V and GND from the board and supplying this to the relay. This power is turned on/off using a NPN 2n2222. This ...
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2answers
203 views

Why do we assume VGS<Vth and Vds>0 for a mosfet in cuttoff and Vce>0 for a BJT in cutoff?

The devices below are both n polarity devices, the BJT is a NPN and the MOSFET is a NMOS. For the BJT in cut-off, why do we have to assume \$V_{ce}>0\$? For the MOSFET in cut-off, why do we have ...
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1answer
198 views

Strange behavior from a circuit, please explain

I was attempting to build a very simple class A amplifier. As far as I can remember from how I have breadboarded simple amplifiers for my headphones before, this circuit is identical to what I have ...
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2answers
2k views

Make adjustable mosfet constant current source

I want to modify this circuit below so the current can be trimmed. The problem is the variations in base-emitter voltage of the NPN transistor. According to datasheets, it is between 0.55V and 0.7V ...
6
votes
1answer
575 views

How to calculate a transistor response time to a square wave?

My objective is to learn how to predict the output to a sqaure wave given R1, R2, R3 and Q1 datasheet (not specifically the 2N3904) without using SPICE or any other software I was looking on google ...