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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6
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2answers
109 views

Why the base current decreases automatically?

Given this circuit: simulate this circuit – Schematic created using CircuitLab I don't understand why, when simulating it by increasing parametrially the V2 from 0V to 12V keeping V1 ...
0
votes
1answer
105 views

Unusual voltage drop at BJT (2N2222)

I'm using BJT (NPN) that is supplied with 7V DC signal at the collecter, 5V DC signal at the base and need a 12V output at emitter. Right now i'm getting 4.35V at emitter. How can i implement it?
0
votes
1answer
62 views

How can I create an SCR using a PNP and NPN?

Several times I have seen an SCR described as similar to a PNP and NPN transistor linked together. But any attempt to replicate the idea seems to fail. In the circuit below, for example, the LED is ...
0
votes
1answer
75 views

PnP NpN transistor circuit, Were would the mic jack go?

I know the circuit says to put the mic jack parallel to the speaker, but im not exactly sure were to put it. Also, could I use another speaker as the mic? This is the pnp npn circuit I found on the ...
1
vote
0answers
58 views

How to calculate voltages on guitar fuzz circuit with pnp and npn transistors?

I have built this circuit on a veroboard, and it seems to me that it has been wired correctly. I do however get a very low output from the circuit, approx 1/2 to 1/3 of the input signal. I reckon that ...
0
votes
3answers
96 views

what exactly is biasing in transistors and how to do biasing

I have read that collector, emitter must be reverse biased in CE configuration in npn transistor but how can n and n be reverse biased
0
votes
0answers
76 views

PNP and NPN transistor used with ARDUINO how to connect them?

This my circuit. What it does is: measuring pressure with MPX200A sensor and looks if pressure under 3 bar, switches on part 1 on arduino (2 transistors) to run DC motor clockwise. If pressure above ...
3
votes
1answer
477 views

Turn 9V device off using 3.3V logic level signal

i'm facing the problem to turn a 9V (battery) powered device OFF using the output of a 3.3V based microcontroller. To do this i already threw together the following circuit (which works - assuming i ...
0
votes
0answers
37 views

PNP collector voltage drop under fan load?

Im trying to build a circuit to drive a fan. Im following an example that i found online. R5 is a 10k thermistor R6 represents the fan to drive (starting resistance 70k). Its a 12v pc fan but it will ...
1
vote
0answers
55 views

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 ...
1
vote
1answer
113 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 ...
1
vote
4answers
92 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 ...
1
vote
2answers
89 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 ...
1
vote
3answers
184 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 ...
2
votes
3answers
343 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 ...
0
votes
1answer
57 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? ...
0
votes
1answer
169 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 ...
1
vote
3answers
197 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 ...
0
votes
2answers
55 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 ...
1
vote
1answer
189 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 ...
0
votes
2answers
501 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 ...
0
votes
0answers
94 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.
0
votes
5answers
210 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 ...
0
votes
1answer
114 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 ...
1
vote
2answers
148 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 ...
0
votes
3answers
107 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, ...
1
vote
4answers
242 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 ...
0
votes
2answers
362 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 ...
1
vote
1answer
155 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 ...
18
votes
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
votes
1answer
696 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 ...
1
vote
1answer
168 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 ...
2
votes
1answer
114 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 ...
0
votes
2answers
197 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 ...
1
vote
3answers
526 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. ...
3
votes
3answers
1k 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 ...
0
votes
0answers
108 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 ...
3
votes
2answers
765 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 ...
1
vote
1answer
203 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
votes
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 ...
5
votes
1answer
801 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 ...
0
votes
2answers
354 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 ...
4
votes
2answers
344 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 ...
1
vote
4answers
657 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 ...
2
votes
2answers
294 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 ...
4
votes
2answers
266 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 ...
3
votes
4answers
953 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 ...
3
votes
2answers
279 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 ...
0
votes
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
votes
1answer
297 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 ...