Questions tagged [npn]

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 current from Emitter to Collector enabling amplification and switching.

Filter by
Sorted by
Tagged with
1
vote
1answer
98 views

Linear regulator heats up at 60 volts

MY goal is to design a regulator which could receive (12 V to 60 volts DC as an input) and 5 volt with 60 to 70 mA current as an output. The reason I used three BJT's NPN (Q1, Q2, Q3), so I thought I ...
0
votes
1answer
38 views

Commute a 12 V siren with an ESP01

I would like to commute a 12V siren with an ESP01. I thought to use NPN or PNP transistors TO-92 that I have since a long time in my drawers. The ESP01 has 3.3V maximum at the output, and the siren ...
0
votes
2answers
57 views

Why does this BJT work as a switch in this logical-NOT circuit, no matter how I orient the emitter and collector?

I have built the following circuit (obtained from Electronics All-in-One For Dummies (For Dummies 2nd Edition)) It works quite well. When the the momentary button (normally open) is not pushed the ...
2
votes
0answers
56 views

How to protect my 555 timer against DC motor noise?

I have this circuit: (Sorry for such a bad schematic.) As you can see, there is a DC motor that gets power from 12V source, using a NPN transistor controlled by a 0-5V signal. Please note that ...
0
votes
1answer
59 views

How do I connect 24v NPN/PNP device to a Raspberry Pi GPIO without cooking the Pi?

As part of my "detecting the presence of an item on a conveyor" I'm looking at industrial through beam connectors. A lot of them are 3 wire NPN or PNP devices like this (highlighted): I'm wondering ...
4
votes
1answer
71 views

Are base resistors of any use for a high-side NPN switch?

I "inherited" a small project from a person I don't know, and I'm navigating my way through it. It's a small gadget featuring a 7-segment LED display. I hear the device's original designer is more of ...
3
votes
1answer
57 views

Transistor cross reference with pinout

I need to find a replacement transistor. The only number I have to go by is a manufacturer (of the unit, not the transistor) part number from 1974 which of course leads nowhere. I know it's a ...
0
votes
1answer
38 views

Find DC components of npn and pnp transistor

I'm sorry but I can't seem to figure this transistor question. The question goes as follows: Draw a DC-circuit and determine the unknown component values. Which DC-voltages ( reference is ground) ...
0
votes
3answers
71 views

What if I switch the place of the load in a common emitter NPN transistor circuit?

As you can see in the picture, there's an NPN transistor in a common emitter configuration. In the first configuration, the load is placed between the collector pin and Vcc, and it is the most ...
2
votes
2answers
515 views

MOSFET and BJT transistors

What is the main difference between a mosfet transistor and a BJT transistor. I know both are used for amplification and can be used as switches. But where would you use one over the other and what ...
9
votes
2answers
2k views

Capacitor in series with transistor base

I am fairly new to electronics and just had a quick question. I saw the following suggestion for a one shot trigger to wake up an ESP from for example a PIR sensor with one shot trigger and to read ...
0
votes
4answers
155 views

When does a transistor turn on

I am having a very hard time understanding when exactly a transistor turns on. For example in the following circuit from Everycircuit: Why does the transistor turn on when the push button is off, but ...
2
votes
3answers
143 views

How I can solve this BJT?

I edited circuit like this: I tried representing currents like: $$ \begin{aligned} &I_{R1}=100_{B1}+I_{B2}\\ &I_{R2}=101 I_{B2}-I_{B1}\\ &I_{i}=101 I_{B2}+100 I_{B1} \end{aligned} $$ ...
1
vote
1answer
117 views

Visual example of NPN transistor

Is the following a correct understanding of an NPN transistor? Basically, a positive voltage source needs to flow through the Base of an NPN transistor and out through the Emitter, so it needs to ...
1
vote
1answer
45 views

Requirements for NPN, PNP transistors

Is the following a correct understanding of what makes a NPN/PNP transistor turn on or off? NPN (more common) Must have voltage > ~0.7V on base Must have (conventional) current flowing into ...
1
vote
1answer
56 views

Turn on LED with the opening of a switch

Hi I’d like a circuit that turns on an LED when the switch opens. I’ve made this so far, but it’s drawing too much current in the “off mode” that it will just drain my battery. Any ideas? I’ve seen ...
1
vote
7answers
753 views

Emitter resistor and biasing voltage

In many articles regarding transistor biasing I see a circuit like below and I don't really get what is the point of biasing like this WITHOUT emitter resistor Re? When emitter branch is connected ...
0
votes
1answer
87 views

How to Convert NPN to PNP transistor?

I'm creating a water level indicator so I can turn on a pump when the water level gets too low. I have NPN transistors, but I would like the transistor to act as a switch that closes when the water ...
0
votes
2answers
35 views

3v output to switch on transistor for 5v fan

Im having trouble selecting resistors for my circuit. I have a 5v supply and my wemos board has a digital pin output of 3v. I want to use the wemos output pin to switch a transistor (BC547) on to ...
1
vote
1answer
91 views

Why do I have to put my transistor after of my component, instead of before?

I'm working on a very simple project, where I want to control a 24V LED with my arduino. Since the arduino can't output that voltage, I have a separate power source, and use a transistor. This allows ...
0
votes
1answer
25 views

LTspice output of a bjt amplifier is offsetted

If I choose "start external DC supply voltages at 0" from transient simulation settings, the output is centered at 4.55 Volts. The amplification and gain is OK, but the output is not centered at 0. ...
0
votes
1answer
62 views

Why does LTSpice simulation give me negative value on NPN emitter current?

So I built this circuit and I am trying to measure the emitter current, and the LTSpice simulation is giving me negative value reading... any idea why?
0
votes
3answers
68 views

Why does a rise in ambient temperature cause a base-voltage-biased grounded emitter stage to saturate?

This is actually exercise 2.9 in Horrowitz and Hill 2nd Ed. which is posed as: Verify that an \$8 ^\circ C\$ rise in ambient temperature will cause a base-voltage-biased grounded emitter stage to ...
1
vote
0answers
56 views

555 timed power at high to low edge in battery powered circuit

I have a lovely Atmel touch sensor whose output is high only as long as it's touched. I want both off-on and on-off edges of its output to initiate two 3 sec pulses (and the time between edges is > 3 ...
0
votes
1answer
33 views

How to isolate sensor power and ground lines as simply as possible

I have an Arduino project that includes three sensors a EC, PH and PPM sensor. The problem is that when you read a sensor the other two sensors affect the reading of the current sensor due to the ...
1
vote
1answer
107 views

Simplest LED-transistor switch LED being on in switch's off-state

I'm very, very new to EE, so this might be a really basic question. I am trying to make a very basic LED-switch using a bipolar NPN-transistor. The circuit I use can be seen below. simulate this ...
0
votes
1answer
67 views

Current through a transistor

I have a problem related with a transistor circuit. Please tell me whether my approach is correct or not. I need to find the current through the 94.6ohms transistor. My approach (Assuming PN voltage ...
0
votes
1answer
45 views

using high and low switch together on a load

in the below picture is a test method im trying to make it work if succeeded, I will implement it in my LED clock project I'm making a four 7 segment LED using 12V led strips as 3x3 bits for every ...
0
votes
1answer
105 views

iv plot for NPN BJT

I have done a “parametric sweep” of the DC voltage source VCC ranging from 0 to 30 V and on the current source with values of iB = 0,50,100,150,200, and 250 µA. Below is the plot iC vs vCE (vCE being ...
0
votes
1answer
54 views

KVL for NPN BJT

Can I write my BE KVL with Rb and Rx in parallel? Also, I am not sure where to include Vbe in my KVL.
0
votes
1answer
63 views

Computing the input voltage that turns the LED on

We assume that the LED will light as soon as the transistor comes out of the cut-off region, therefore the BJT is on and operates in the active region. I know that that Vbe = 0.7V, Ib>0, ic=BIb and Vce>...
0
votes
0answers
33 views

Is Q-Point in Transistor constant? For different configuration if same transistor is used?

Via IV-Characteristics, for specific Ib, I got the Q-Point and using the same value of the Q-Point, I constructed a common emitter configuration biasing circuit that its V_ce = Q-Point_Voltageafter ...
1
vote
0answers
54 views

Reading high voltage output NPN proximity sensor with Ardunio YUN

I have a NPN proximity sensor with rating voltage 6-36 VDC. (https://www.amazon.co.uk/gp/product/B07SD9VYDH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) To power it up, I use a 24 VDC power ...
0
votes
3answers
139 views

BJT Low Current Consumption Amplifier

I'm trying to amplify a 20mV ptp signal to something around 1V ptp. I intent on only doing this in one stage and require the amplifier to be very low power consumption (3.3V supply max 1mA for entire ...
1
vote
2answers
72 views

Voltage at Collector of NPN less than Minimum allowed for High

I have connected the collector of a NPN BJT (DTC144EE) to the Power_ON pin of my lte module (HL7588). The pin is internally pulled up by a 100k resistor to 1.8V. The module is powered on by driving ...
1
vote
0answers
50 views

Simulation of an Electric Shock Box

This is the continuity of this: Understanding Electric Shock Box Circuit I really don't understand what is going on, so I was hoping that simulating the circuit in Proteus might help What parameters ...
0
votes
1answer
80 views

BJT Circuit Current

I have a question regarding the circuit below. I am unsure how to calculate the current flowing through the 1k resistor. I think it is reasonable assumption that the collector of the PNP BJT must ...
1
vote
2answers
191 views

NPN common emitter transistor as a switch switches off as the current draw in collector falls

I am trying to switch power to a Pi Zero using an NPN transistor (2N2222) as a switch, as in the following diagram. simulate this circuit – Schematic created using CircuitLab The Ib is around ...
0
votes
1answer
61 views

How to determine transistor specification range for voltage and current (in relation to design requirements)

Attached is my current circuit for using a 5V logic output device to control 24V going to a load with max current draw of 14mA. (Ignore the name for transistor Q1, that is just a random NPN BJT). ...
1
vote
4answers
101 views

Current booster for relay

I have a DC power source which can provide up to 5V, 50mA (LabJack maximum output current, voltage bus-powered) and I want to power my relay (SDT-S-105LMR2,000) with 5V, 100mA. I have an option to use ...
1
vote
1answer
87 views

Driving NPN with Raspberry Pi

When driving an NPN transistor using the GPIO output on a raspberry pi I assume no protection is needed on the GPIO side of the circuit? So nothing would really be needed beyond this to drive the ...
0
votes
1answer
82 views

Do transistors naturally have resistance on base, collector, and emitter?

I'm using a circuit simulation app called EveryCircuit, and for the npn transistor settings it has forward beta, reverse beta, base resistance, collector resistance, and emitter resistance. I'm a bit ...
1
vote
3answers
82 views

Fundamentals of Output Characteristics of a BJT, what is the difference between load line and output characteristics?

In any transistor, we plot the output characteristics, i.e. effect of change in Vce on Ic. Next, we write the KVL equation on the transistor, i.e. Vcc = IcRc + Vce and plot the load line from this ...
3
votes
1answer
73 views

What are the functions of these components in this 15V 500mA power supply?

Hello guys, I want to know what is purpose of the transistor T3 (BC547B) in this circuit. I understand it provides base current to the series pass transistor T5 (2N3055). Also I want to know: What is ...
0
votes
0answers
47 views

BJT Latching Circuit Help

I have build a latching circuit using both a NPN & PNP BJT to turn on and off an LED, as shown below: simulate this circuit – Schematic created using CircuitLab When I built the circuit ...
0
votes
0answers
33 views

Calculating Nmax in loaded bipolar junction transistor inverter

I have tried various methods for calculating N max here, and some have resulted in negative answers while others have resulted in an answer of around 1. Is my method correct? Or am I missing ...
0
votes
2answers
111 views

Bipolar Transistor Inverter Circuit Analysis

I have been trying to understand this question and I'm just not sure what equation to use for the collector current. I'm not sure if I need to be using an output voltage function of time? All I have ...
0
votes
2answers
97 views

Why is current flowing mostly through the base (NPN transistor)

I am currently working to install an NPN photoelectric sensor (retro-reflective dark on: https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/photoelectric_sensors/18mm_round_-...
5
votes
2answers
831 views

Basic transistor circuit

I'm playing around with a BD179 transistor, trying to get my LED bulb to light up but without luck. My mistake is probably something very simple but I'm learning so bear with me.
2
votes
2answers
276 views

TL431 / TLV431 supercapacitor voltage clamping circuit

I have a question regarding a circuit I've been working on for some time. The circuit is based around existing supercapacitor protection modules and uses a TL431 (actually a TLV431 lower power ...

1 2 3 4 5 11