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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Why do you put the load of a transistor on the collector side and not the emitter side? [duplicate]

Everything that I have read has said to put the load on the collector side and connect the emitter to ground directly, but I am having a hard time understanding why this is. Why do both PNP and NPN ...
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Weird NPN transistor symbol with a box connecting all three pins?

I've come across this symbol in the datasheet (link below) of a transistor for a halogen "electronic transformer" that uses two in a half-bridge operating at about 35KHz. The datasheet ...
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NPN high-edge flipflop [closed]

I'm looking for a design of an NPN flip-flop that reverses its output when the input is brought high. I'm looking to use the 2N2222 for this purpose.
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1 answer
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5V Input and Output interfacing with 3.3V GPIO [closed]

I have a device (a motor drive) with 5V logic. My controller is 3.3V. I draw the two circuits. The right sides are fixed in the device. I have some exact questions about calculations. -...
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1 answer
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Shift register does not output voltage [closed]

I am building a 8x8x8 LED cubic matrix based on an Arduino. My schematic and PCB design was based on the one posted by Tapendra Mandal on Youtube. When I finally connected everything and try to write ...
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1 vote
2 answers
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Stopping reverse flow of current

The above circuit has two sections. Section A is a simple transistor as a switch circuit using BC547 NPN transistor which triggers a LED1 as well as section B. Section B is a NOT gate circuit using ...
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2 answers
127 views

Increasing the forward voltage required of the PNP transistor?

I am a newbie and was reading about the uses of a 555 TIMER. I came across a project to create 40 LED Bicycle Light in Led Circuits. I can understand the diagram and most of the explanation except ...
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NPN transistor to turn ON an ATTiny85 from a pinout of an ATTiny85

I have 2 ATTiny85 and a NPN CS-9011 used as a switch. They are both powered by the same 3.3V. I use pin 1 to run the base of the transistor with a 1K resistor. This is not working after an afternoon ...
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Advantages of using 2 NPN transistor NOT gate

Is there any benefit using 2 NPN transistors for a NOT gate rather than one NPN transistor?
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1 answer
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Increase the voltage in a simple NPN circuit [closed]

I'm building the circuit described here, but I need to tweak it a little. I need a stronger magnetic field from the coil to move a bigger 'swing'. So I want to increase the number of turns on the coil,...
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5 votes
3 answers
1k views

Transistor as a switch driven by a square wave

I'm trying to understand how to use a transistor as a switch. I'm sure I am not doing this right. The input signal is a simple 30 kHz square wave, 3.3 V amplitude. There is a second gate signal which ...
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With a transistor (as a switch), does the order of the parts matter?

I've wired up my project(s) similar to how they're laid out in A to control whether or not an LED is on or off. It works fine (as far as I know), but I've seen lots of examples online of circuits laid ...
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Common emitter amplifier with low impedance

The following schematic shows a common emitter amplifier driving a resistive load. The common emitter has a high output impedance, is it possible to use the amplification achieved with the common ...
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Design of transistor amplifier for nanosecond signal (with NPN transistors)

For a project/learning experience I want to design/build an amplifier. The signal I’m provided has an approximately 1ns pulse width (duty cycle of 1%) with a peak of 2.2V and a repetition frequencyof ...
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2 votes
1 answer
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Why does my transistor explode in a simulator?

I'm new to electronics and I can't identify the reason why my transistor explodes when I simulate it. I am simulating a simple common emitter amplifier with a power supply of 12 volts.
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NPN Transistor amplifier - Base emitter amp

I would like to understand/create a circuit which amplifies an input signal with a base-emitter follower. Sadly, I’m not getting any amplified signal at the output. I don’t really understand why on ...
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4 answers
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What is the maximum voltage applied to NPN transistor base? (like for MMBT3904)

I cannot really find out what the maximum voltage one can apply to the base of the NPN transistor in a circuit like this one is. I highlighted the base in question. Can I apply more than the typical ...
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Correct way to drive a 12 V motor from an Arduino with an NPN transistor

Looking for some help vetting my circuit design, it's been a long time from my college days messing with electrical stuff. My plan is to have an ATMEGA328 with the Arduino bootloader driving a 12 V ...
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BJT NPN transistor

I am confused on a topic regarding NPN BJT transistors. When there is a collector-emitter voltage (VCE) applied to the NPN transistor (as shown in the figure) without a emitter-base voltage (VBE), it ...
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Switching the GND of a Wheatstone bridge using NPN

I am trying to turn on and off the power supply to this bridge by using a micro controller. Can I use the following switch using an NPN ? Edit: A switch using a MOSFET - a better option?
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3 answers
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What is the role of the diode in this heat sensor circuit?

simulate this circuit – Schematic created using CircuitLab I am building a heat sensor circuit using this circuit model. What I understand is that the \$\beta\$ parameter of the NPN transistor ...
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BJT type Gilbert cell does not work

I designed a Gilbert cell for analog multiplication, all the transistors (NPN) are in active region as I checked one by one, however, the result does not seem correct at all. How can I make it better? ...
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(Update)Using a bidirectional optocoupler for attaching any PNP & NPN sensor type [duplicate]

I have two different 12 V PNP & NPN proximity sensors. My first design was for each sensor type, having an identical PCB design with a normal optocoupler with a dedicated wiring arrangement. My ...
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What type of npn /diode is this?

I try to replace a sot 23 npn. The only markup is "NV" . It's used to switch a relay. I tested it with two transistor tester. Both of them show me a diode with the npn symbol. I dont know ...
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1 answer
102 views

Why doesn't the current in a BJT transistor depend on the emitter-collector voltage?

In my understanding, in an NPN junction for example, an increase in the emitter-collector voltage should widen the depletion layer in the base-collector junction therefore increasing the electric ...
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Why do we need to connect the load before NPN transistor [duplicate]

I am trying to use transistor as switch and getting confused with the workings. For a NPN transistor, Collector needs to be connected to +ve and emmiter to -ve. If we look at the schematics below, in ...
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How to include the Early effect in NPN BJT current equation?

To understand the NPN current equation derivation, I have been studying my lecture handout and the emitter current equation accordingly is found as : \begin{equation} I_E= q n_i^2 A(\frac{D_p}{N_{dE}...
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How does class AB amplifier biasing work exactly? [duplicate]

Can somebody please explain in both cases the biasing method? I don't understand the following points: It's OK that we need ~0.7V for PNP and NPN base-emitter voltage, that's why a diode is used for ...
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2 answers
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A paradox in relay drive circuit

According to the circuit shown below: If we assume a Vbe of 0.7 V for Q1, the base current of Q1 is (5-0.7)/100 = 43 μA, and assuming a β of 100 for Q1, we have a collector current of around 4.3 mA. ...
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6 votes
6 answers
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Why does this NPN transistor operate differently if it comes before the switched element?

I'm simulating turning an LED on with a transistor switch in LTSpice. To my bewilderment, the current through the LED in Circuit 1 is ~51 mA and the current through the same in Circuit 2 is only ~6 mA....
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2 answers
208 views

How can I find operating point in this curcuit?

I made a schematic in LTspice like in the first picture and then solved the question in second picture for Rb=100k. I have found Ib=0.03 mA, Ic=4.5 mA and Vce=-0.836 V but when I checked the graphic ...
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3 votes
2 answers
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Why does this LTspice schematic simulation have five pen plots?

I ran the schematic at the first picture but it gave five graphs like in the second picture. Is there a mistake?
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1 answer
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Drive NPN from Voltage Regulator?

I am trying to get two disparate camera systems to talk to one another, specifically an Arri camera with a Preston system, and specifically to transmit a tally signal when the camera is recording. ...
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1 answer
132 views

'Unknown Voltage Requested' error in LTspice

I made the schematic that is in the first picture and I wanted to plot Vcc vs. Vce but when I tried to plot, it gives an error like in the second picture. How can I fix the error?
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1 answer
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I can't simulate this circuit in LTspice [closed]

I can't simulate the circuit in this picture. When I try to run it gives an error for missing I value. Could you help me? Could you tell me what Vce and Vbe are?
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2 votes
2 answers
826 views

NPN transistor with no resistance at collector?

I'm trying to work my way through a pretty simple laser-based communication system (full description here) project I found online, just as a learning experience. I'm having issues understanding the ...
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0 votes
1 answer
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N-MOSFET and NPN latching switch

I've seen many latching circuits through searching and reading some simple circuits. Most use NPN+PNP combination, some bistable ones use two NPNs, some use DPDT relays. Is the following circuit going ...
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0 votes
2 answers
204 views

2N2222 NPN transistor base resistor calculation

I am quite new to electronics. I am trying to control three LEDs with an Arduino using a transistor. I was wondering what the base current limiting resistor value should be. I looked around the ...
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1 answer
155 views

How to receive input signal on Raspberry pi GPIO from transistor emitter

I'm trying to build a simple circuit that allows a Raspberry Pi to detect AC voltage in piece of wire inductively. I have the following circuit which basically uses an antenna wrapped around the wire ...
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5 votes
3 answers
1k views

NPN transistor resistor from base to GND. Is this useful?

I have a circuit where many NPN BJTs are interfacing 3.3 V GPIOs with higher voltage circuitry. Each application has a similar setup to the image below (resistor R422 is what's in question). I did ...
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1 answer
171 views

Why is the depletion layer near the emitter region narrower than the collector region?

While studying Grob's Basic Electronics chapter 28 I came across this statement, Notice in Fig. 28–2 that the EB depletion layer is narrower than the CB depletion layer. The reason for the different ...
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3 votes
1 answer
122 views

A question related to a NPN transistor having a DC bias

β = current gain I made the circuit of the above picture with LTspice. (A graph of Vce) (A graph of Vbe) And I was able to get 4.2966V for the value of Vce and 0.6543V for the value of Vbe. However, ...
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1 vote
2 answers
60 views

Input selectivity for a RF receiver pre-amp

In his answer to my question about common emitter amplifiers, @glen_geek commented that the RF receiver pre-amp I used as an example (shown in Figure 1) was "too simple" and that "any ...
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2 answers
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NPN Transistor Switching - Negative Gain Calculated and Not Switching off Fully = Blown Transistor?

I have the attached NPN transistor being switched by an MCU. I've made some measurements and done my calculations as a result of observing that the NPN is not fully switching off (the relay stays on). ...
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1 vote
0 answers
70 views

BJT common emitter output conductance

I constructed in multisim a common emitter circuit from the following diagram where the lower Keithley is used to supply VBE and the upper Keithley is used to supply VCE. I obtained the IC- VCE ...
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1 vote
3 answers
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Sticky/Intermittent Relay Driven by MCU and NPN Transistor

I have an MCU (1.8 V logic levels) driving an NPN transistor to turn an relay on/off. The relay has a 12 V DC coil with resistance of 1028R per datasheet. This would require a current of 12/1028 = 11....
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3 answers
119 views

Transistor resistor calculation help (design revision 1)

I posted my original design yesterday and got many comments about my errors. This is revision 1 of my design. I am now pretty sure I have the load resistors calculated correctly, but still unsure ...
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1 vote
1 answer
112 views

Transistor Resistor Calculation

I am new to electronics so I'm not too sure about how I should be calculating the base resistor to use in this circuit. I think the load resistor is calculated correctly (data sheet at bottom for ...
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3 votes
2 answers
217 views

When switching an LED with a transistor via a microcontroller, do I have to worry if the load supply voltage is higher than my microcontroller logic?

I want to turn a white LED on and off via my microcontroller GPIO. The ESP-01S board that I have uses an ESP8266 chip, which has a limit of 12 mA GPIO output current. However, I want to drive this LED ...
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-1 votes
1 answer
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NPN BJT Operation - What does it mean for the Collector - Base junction to be reversed biased?

According to this screen grab the Collector Base junction must be "reversed biased". I seem to be confused about the meaning of that. I thought that the Collector needed to be at a higher ...
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