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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2answers
44 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
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3answers
99 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
489 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
50 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
712 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
130 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
448 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 ...
3
votes
1answer
112 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
174 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
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2answers
186 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
312 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
138 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
214 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
270 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
177 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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votes
1answer
422 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
139 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
196 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 ...
0
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2answers
207 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 ...
1
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3answers
396 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 = ...
0
votes
1answer
162 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 ...
0
votes
1answer
142 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 ...
4
votes
2answers
117 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 ...
3
votes
1answer
172 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 ...
0
votes
2answers
957 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
320 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 ...
3
votes
1answer
203 views

NPN transistor circuit connection, what determines which region it is at?

I know that for an NPN transistor to be in the active region, the base emitter should be forward biased and the base collector should be reverse biased while for the NPN transistor to be in the ...
0
votes
2answers
140 views

How to pull low with a transistor? [duplicate]

I have a 3.3v line, which I will need to pull low intermittently with a microcontroller to send data. I have tried using a BC547B NPN transistor (also tried BC337, BC517 and BD139) with the Collector ...
4
votes
3answers
1k views

How do I check a BJT transistor if it is still functional?

Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective? simulate this circuit – Schematic created using CircuitLab Say ...
5
votes
3answers
247 views

NPN transistor seams to be “leaking” in simulation. What is wrong with my circuit?

I am kind of new to electronics, and I am eager to learn how to work with transistors; especially in realizing logic gates with them. I tried to build a very basic circuit with a transistor as my ...
2
votes
3answers
259 views

Effect of a transistor on a voltage divider? (or vice versa)

I'm learning about transistors and am trying to make a basic circuit that uses a photoresistor as a sensor to turn an LED on and off depending on light conditions (the 150kOhm resistor is where the ...
2
votes
4answers
148 views

Different answers when using two different equations to find the same unknown (BJT)

Problem 43, chapter 6 in sedra and smith microelectronics. simulate this circuit – Schematic created using CircuitLab We are asked to find the current flowing in R1 and R2 knowing that ...
2
votes
2answers
370 views

XOR Gate design problem

I just recently started trying out on electronics engineering, and have built a OR gate, NOT gate and a AND gate using NPN transistors. When building the XOR gate, this is my design: However, SW2 ...
8
votes
4answers
2k views

Transistors in parallel

I want to use several transistors in parallel to control current through a load. This is to distribute the current through the load across the transistors so that individual transistors with a rated ...
1
vote
1answer
339 views

Explain the use of NPN and pMOSFET in this 8x8x8 LED cube

I've got part of a circuit diagram for an 8x8x8 RGB LED cube from http://www.kevindarrah.com. See the entire schematic. I'm having trouble working out how it does what it does. I know that a high ...
2
votes
2answers
208 views

Bipolar transistor static forward current transfer ratio

My book (teach yourself electricity and electronics) talks about the static forward current transfer ratio ... ratio of collector current v.s. emitter current when we place the base at electrical ...
0
votes
1answer
356 views

Transistor as switch dropping voltage

I'm using an Arduino to drive two hobby servos but they draw too much current when not in use so I'm trying to use a transistor as a switch to cut the power to them when not needed. simulate ...
2
votes
3answers
930 views

Sinking and sourcing current

I have been reading that NPN transistors are sinking and PNP are sourcing devices. I do not really understand this concept. It says current source device connects load to Vcc and current sinking ...
0
votes
1answer
440 views

NPN Transistor Behavior with Base Voltage higher than Collector

Lets say I have this circuit: simulate this circuit – Schematic created using CircuitLab I think if I apply a 0 to the base of Q1, I'll develop something like 4.3V at the collector of ...
2
votes
1answer
595 views

Using an NPN vs a PNP transistor

Is the following circuit electrically sound? My recollection is that the right way to do it is to use a PNP transistor on the high side and an NPN transistor on the low side. Will it work if they are ...
6
votes
2answers
1k views

Single LED single transistor circuit not working

I was making a circuit with 1 LED and 1 transistor. pretty primarily i was trying to use the transistor as a normal switch. Here is the diagram below. So, this is an NPN transistor and i connected ...
4
votes
5answers
335 views

NPN BJT in saturation, base voltage irrelevant?

I'm trying to build as simple a circuit as possible that will pull a logic line low every time an automotive ignition coil 'fires'. My first inclination is to simply attach the 'negative' terminal of ...
1
vote
2answers
748 views

How the transistor NPN 2N2222 works?

I'm a beginner to electronics. I just started to test transistors, but I've some doubts. I've used this schematic to test a NPN 2N2222: My questions: 1 - How much Voltage or Amps should the ...
1
vote
1answer
231 views

How is it possible that shorting base and emitter allows current to pass?

My setup is simple: a NPN transistor is connected to a DC motor and a battery. The series goes like this: positive terminal - motor - collector; emitter - negative terminal. The transistor base is a ...
2
votes
2answers
1k views

How does the collector emitter relationship work with a transistor?

So, I'm not understanding how NPN transistors really work in this scenario. In this image, I have highlighted what I understand to be the collector and emmiter. My understanding is that power ...
0
votes
3answers
270 views

How to control 0 to 110 of AC with microntroller rms output of 0 to 5 v

Is it possible to control high current with small rms voltage? UPDATE Do you think that this is gonna work?
0
votes
2answers
106 views

Why is the base currect incorrect?

My multimeter shows: Ib=218uA why? But my calculation shows, it should be: 8.5uA I used the formula: Ib=(3.1-0.7)/(10k+271k) [I take Beta=270, BC548 transistor.] What is the problem? Why is Ib = ...
1
vote
1answer
263 views

What NPN transistor should I use?

I need to control a 12v 5A (or 3A if need be) with an Arduino UNO which has 5v and 40mA. I, unfortunately don't know how to read transistor data sheets. What NPN transistor should I get for this ...
10
votes
3answers
4k views

How do I get +5v for loud noise, 0v for silence from Electret Microphone (or other components)?

I have been asking a few questions here to get to a proper one, the initial questions I asked are linked to at the end. I used Fritzing to make up some schematics of my initial thoughts, but at the ...
9
votes
1answer
4k views

Can the Common Emmiter Amplifier use a PNP Transistor instead?

This is a simple Class A amplifier using an NPN transistor: Is there a way this can use a PNP transistor, instead (with only 0V and +Vcc, not 0V and -Vcc)? Why or why not?