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.

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2answers
761 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.
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75 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 ...
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1answer
59 views

Activating Relay Coil (NPN and MCU)

Circuit primitive in CircuitJS First, I'm having a hard time with transistors, and only recently managed to pass current through a NPN as planned (70-ish mA from 5 V with a 325 hFE 2N3904 with a 10K ...
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125 views

NPN Transistors Not Working When Emitter Is Grounded

I'm trying out transistor logic for the first time using PN2222 transistors that came in a kit that I got from Amazon. I've been running into some problems with making a basic NOT Gate (as shown in ...
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1answer
63 views

Can I use 13003 transistor in place of 2n2222?

I am working on a project which requires a npn 2n2222a transistor as recommandation. But as of now the transistor is not available to me. Alternatively I have transistor 13003 and c945 available as ...
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2answers
112 views

Correct way to control 12V relay from a Raspberry Pi

I am working on a project where I need to control a couple of relays from the GPIO header on a Raspberry Pi. I tried getting a PCB with the layout like the right version in the image below, but I ...
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1answer
88 views

How many NPN common emitter transistor circuits are there? [closed]

I'm studying for an important exam, solved a lot of common emitter circuits with different unknowns. Most of them them look similar. Can someone give me some examples or exercises of circuits of NPN ...
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1answer
83 views

Delay circuit with capacitor and transistor doesn't work as expected

I made the following delay circuit. According to the simulation, it should take in the order of seconds for the relay to switch. Instead what I find (even by varying the resistance of the second stage)...
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2answers
69 views

Modify DPDT push button with an NPN to control with GPIO?

I have an 2-port HDMI switch that swaps inputs using a 6-pin DPDT latching push button. I want to modify it to be controlled by a GPIO pin on my Pi rather than having to push the button. One way that ...
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1answer
56 views

How can I prove that Vce saturation lies below .2V?

When I try to prove that Vce for saturation is below .2V and I take npn transistor I simply consider emitter to be at 0V and thus base emitter junction being forward biased base gets a voltage of (.7 ...
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1answer
43 views

NMOS to NPN Circuit Analysis

I am attempting to us a voltage shut off switch with some pre-existing hardware. I do not understand transistors well enough yet and am looking for clarification. I desire for V2 to be able to go to ...
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1answer
58 views

Use of D3 and D5 in inverting circuit

I have simulated this circuit in Spice and it works as it is supposed to, but I fail to understand the use of diodes D3 and D5. I know it has something to do with T2 transistor. Edit: Correction ...
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2answers
78 views

How to derive formula for emitter current flowing through Re?

Ie = Ve/Re I was thinking about using that approach but i have been doubting myself if that is the right approach to go with, because then i have to express the emitter current in term of alpha and ...
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1answer
228 views

Understanding a PNP/NPN LED schematic

I bought and soldered a dirt-cheap flashlight kit from China. I'd like to understand how it works, though - specifically, why it uses a combination of a PNP and an NPN transistor (schematic from the ...
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2answers
53 views

Switching circuit transistor NPN, load has voltage and current though transistor is off

I am confused about the switching of this circuit. I can control the V1 input line. Output line is R4 load line. My Vbase (V1) is 0V, and Vbe is 0V. Transistor is off and collector should see 0V. That ...
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1answer
31 views

electrons of the collector in NPN transistor

What happens to the electrons in the N region of the collector of npn transistor that operates in active mode ? I know that electrons coming from emitter split to base current and collector current ,...
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1answer
73 views

Working region of NPN BJT

I have come across the following circuit where a BJT works as switch when I apply 23 volts to base using a 100k resistor. A 3.2 mA constant current source is connected to the collector of the BJT ...
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4answers
783 views

TIP120 Transistor + Solenoid Failing Randomly

I am using TIP120 transistors (controlled by 74HC595 shift registers) to control 12VDC, normally closed solenoid valves. Everything is working in short-time tests however when left overnight, some ...
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1answer
161 views

555 IC - Transistor Tester

Why are Pins 7 and 5 floating for this 555 IC and how does an NPN and PNP transistor when connected to E B C act a switch? Without the use of Pin 7 surely the capacitor cannot discharge which would ...
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28 views

Selectable sink or source Input

I'm looking for a circuit that I can add to a universal Input board that will be able to handle a 5-24v input PNP or an NPN 0v signal that I can connect to my arduino. I was considering using an ...
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1answer
37 views

How to activate a solenoid using TSOP4838 IR receiver

I have a TSOP4838 whose output is 5v normally and 2.5v when I press a button on my DVD remote. I wish to activate a solenoid when the DVD remote button is pressed. The circuit is is powered by a 9v ...
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2answers
163 views

NPN: Not fully sinking to GND

I'm using an NPN to pull a 12v (5mA) signal low from an MCU (logic level). My problem is that when I pull the 12v line low, 7.4v are still present at the 12v side of the line using the circuit below: ...
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1answer
57 views

555 timer square wave LED flasher

Will this circuit work for the purpose of making a high voltage LED flash on and off at 10kHz? I have a NPN transistor to turn the LED on and off. The pad is where the LED will be soldered into as ...
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1answer
86 views

Transistor latching circuit

I have made the following circuit from a few online sources, it is very basic but uses two NPN transistors to make a latching circuit that toggles when either push button goes to ground. My Falstad ...
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2answers
61 views

Using transistor as switch in the “middle” of the circuit

I have an rather complex circuit with button micro-switch in the middle (actually, it's RF remote control with 3 buttons). I would like to be able to simulate the micro-switch click on it with one of ...
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1answer
54 views

LED cube using 74HC595 and 2N2222

So I'm trying to build an 8x8x8 LED cube according to this Instructables. But I'm using slightly different parts: 74HC595 shift registers instead of 74HC164 2N2222 transistors instead of 2N3904 I'm ...
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2answers
47 views

ESP8266 GPIO2 - invert logic NPN transisotr

I make big mistake in my design. I connect output to ESP8266 GPIO2 at this pin I got base of NPN transistor to control LED. I test it on breadboard but probably by noise or "universe magic floating ...
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0answers
51 views

Push-pull transistor - input current spikes and advantage over just an npn transistor

I have simulated the following circuitry in LTSpice: Input Voltage pulse characteristics: Questions: 1. What is the reason for the current spikes on the input resistor R2? Do I need to worry about ...
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1answer
64 views

NPN transistor won't saturate when Vcc is greater than 7 volts

Am I missing something here? I have an NPN transistor (2N2222) with a 10K resistor from collector to Vcc. Also a 10K resistor from base to input signal. Emitter is grounded. The base input is ...
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2answers
73 views

Using an analogue multiplexer to control a motor controller?

I am designing a control circuit for a Sabertooth 2x60 motor controller. When this controller is in analog mode, it runs in full reverse (0v control signal) until my software starts and applies 2.5v ...
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3answers
85 views

NPN inverter alternative that takes up less space on the board

Here I have an NPN inverter circuit which consist of 2 separate NPN transistors and 3 resistors. It does the job, but it takes too much space on the board. Is there any alternative to this circuit ...
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1answer
315 views

“Normally closed” switch with NPN transistors

Is it possible to have "Normally closed" switch with NPN transistor when the voltage at the base is 0V? So far I only managed to achieve this result with NPN transistor when the base is HIGH. When the ...
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1answer
80 views

12 V pulses with 100 MHz repetition rate

I have to control an high impedance load (> 25 MΩ) with 12 V pulses with maximum 5 ns of width and a repetition rate of 100 MHz. I can generate the pulses with the required shape using an FPGA ...
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1answer
147 views

Can a BJT base-collector junction be safely used as a diode?

In a (hobby) project I'm doing, I noticed that the diodes I needed were more expensive than the NPN transistors, which left me wondering if I could substitute the transistors for the diodes. I'm ...
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1answer
55 views

Question about transitor NPN [ALFA;Strange configuration;Exit characteristic]

first of all thanks for read and for your time, I have a few questions about transistor: 1) I can't understand why my book say: Ic=Icb0+alfa*Ie and not ...
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1answer
39 views

Half H-bridge using only ntype mosfets or npn transistors

Would the following circuits work? I keep thinking I need a mixture of ptype and ntype mosfet or npn and pnp transistor for a half h-bridge, but I keep seeing schematics with only ntype mosfets or npn ...
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1answer
135 views

Trouble turning on relay using PNP transistor

I am having problems turning on this relay: https://omronfs.omron.com/en_US/ecb/products/pdf/en-g6qe.pdf Using a transistor whose base is connected to a digital signal of an Arduino Nano. The ...
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4answers
831 views

Constant Current LED Circuit

In the below circuit, the circuit maintains a constant current on LED. My question is after the LED there is a voltage of 18V, still, need to be dropped. Will the NPN Transistor heat up while ...
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0answers
48 views

MCP73831 stat pin current

I'm trying to implement a bi-color LED connected to a Microchip MCP73831 battery charge management controller, so I can switch between red and green LED output. Currently my circuit is mixing them ...
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Why do I have voltage on Collector and Emitter when NPN transistor turns on? How to get rid of it?

I have a 2N3904 NPN transistor. I'm feeding the base 5V. the transistor turns on just fine and it shorts the collector and emitter. However, when I turn my meter on volts, I read around 1- 1.5 volts ...
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2answers
49 views

Spike in RTL Inverter

I do not understand the cause of this spike which can be observed in an RTL inverter (but also in a CMOS inverter). In the following image it is the peak at 10 mS (I have considered as input a signal ...
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0answers
49 views

Driving transistors without using MCUs

I'm trying to drive transistors with just a push of a button without using a MCU. The circuit I drawn drives different transistor on every button push and resets back. First part is a debounce circuit ...
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1answer
116 views

NPN Transistor common emitter calculation

I built the following circuit in LTSpice using the default NPN BJT model (beta = 100). I calculated the Ib to be 115.754uA. This is how I did the calculation: Equivalent voltage at base is: ...
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40 views

Using a PNP to enable a NPN current source not yielding expected current

Hi I am trying to switch on a brake light with a reed switch. The load is a 12v (0.1A) LED bike light. The following circuit works in the sense that the light comes on when the magnet moves away from ...
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0answers
147 views

complementary transistor pair npn/pnp in the Kapustinsky circuit

I need to create an old circuit that reproduces fast impulsion, the Kapustinsky circuit (see the picture). This circuit is 33 years old, and a transistor (or equivalent) does not exist anymore, the ...
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2answers
78 views

How can I dampen current spikes when using NPNs to drive an LED

Hi I have the following circuit, its purpose is to flash an LED once per second. I'm using a pair of transistors as a constant current source but I observe current spikes of 20% or so when it is ...
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1answer
108 views

How to set fixed bias on transistor 2N2222 for certain specifications?

I'd like to ask how to set fixed bias for this transistor.. It doesn't seem to be working. If anyone know how to calculate it, please tell me. I wanna adjust two resistor values so that Uce = 5,44V, ...
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2answers
190 views

555 timer circuit switching automotive solenoid with PNP & NPN switching transistors

I am trying to design a 30 second timer circuit to switch an automotive solenoid that draws about 0.8 amps, and need some help please. StackExchange posts have been very very helpful so far, and by ...
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1answer
86 views

BJT common collector amplifier with a voltage gain sligthly higher than one

How could I explain why a common collector amplifier has a voltage gain higher than one ? In a lab session, I built this circuit : With Vg=30 mVpp and Vcc=15V, students were asked to give the voltage ...
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3answers
117 views

How to configure NPN transistor as switch and adjust current flow?

Consider the following circuit: As signal a 100 kHz square wave (between 0 and 5 volts) generated by an Arduino. I want to control the transistor so it will let the current from the supply pass ...