BJT stands for Bipolar Junction Transistor. It is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications.

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Getting bad clipping issues with this 3 stage amplifier

What am I using? 3 stages of amplification. An input voltage of 10mV peak or 20mV pkpk into the first stage. 1st stage: NJFET Common Source. Using a voltage gain of 3. 2nd stage: NPN BJT Emitter ...
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How much can BJT parameters (particularly beta) vary for Monte Carlo analysis

Background / Requirements: I'm designing a typical Class AB amplifier using diode-connected BJTs to achieve the biasing. I have a requirement to keep the total quiescent current at room temperature ...
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94 views

How to eliminate the Miller effect on BJT BC547?

I have an application: The input in a 3V train pulse @ 100Khz I need an Ic to be 10mA for the LEF of the optocoupler. I am using BC547C: Input Capacitance= 9pF Current Gain Bandwidth ...
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225 views

Semaphore using one microcontroller pin

I'm trying to make a semaphore using to LEDs green and red, controlled by one arduino pin. Idea is when pin is low red LED is on and green LED is off, when pin is up green LED is on and red LED is ...
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48 views

NPN BJT used for DC Switching Load [on hold]

I am trying to learn some things for a class. This is not homework, just studying for an exma. It has to with calculating values when using a NPN BJT. I have five (only three because other 2 were not ...
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29 views

BJT Circuits at DC, base current calculation

I'm trying to walk through the example calculations in the attached example however I cant understand how the author gets the expression for the first step in the process. I tried making up the ...
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42 views

Viability of Voltage Controlled Amplifier circuit

As part of the synthesizer project I have been working to design a simple voltage controlled amplifier. Due to the complexity of other parts of the circuit and the amount of time I've spent on this ...
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60 views

What does “2N363PNP” mean?

Recently I did the experiment of input and output characteristics of BJT and I saw that "2N363PNP" was written on it.I want to know what does it mean? Is it only a name ?I can guess that it is a PNP ...
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16 views

How do I find transconductance gm in this exercise?

We have the following exercise : I have questions regarding a) and b) For a) the solution is As for b) you can kinda see it in the above solution that IE=0.5 mA ,I think that this is because ...
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158 views

What (if any) is the leakage current through a NPN (C-E)?

So I have a circuit where I need the current consumption to be low. Therefore I am using a 10M\$\Omega\$ resistor to 'pull-up' the pin on a chip which will need to be switched between high and ground ...
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61 views

Alternative ways to maintain temperature stability of silicon BJT circuits other than feedback resistors

So I've been messing with Bipolar Junction transistors lately and I'm trying to really nail the concepts of designing circuits with these things cause I want to start using them in some of my circuits ...
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58 views

Design a BJT Amplifier [on hold]

Designing a multi-stage BJT amplifier that follows these rule Avo = 100 without load Input resistance of 75kohms + Output resistance of 100 ohms - Beta of the transistor is 100 Is there any way ...
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77 views

Battery Recharge Circuit Help

Can you help me understand how this circuit works? I really don't understand the resistor connected to the 0V rail. How does the BJT ever turn on?
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69 views

Multi-stage amplifier coupling

For my final project in my electronics course this semester, I need to design an amplifier with a specific set of parameters. Specifically, it needs to have a gain of 100, a voltage swing of at least ...
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38 views

Can you explain this differential amplifier exercise to me?

So we have the exercise in the figure The figure is The solution according to the book is VE=-0.7 Volt thus I=(-0.7+5)/4.3=1 mA so re= 50 ohm.Why is re=50 Ohm here? a) Ad=V0/Vd=α*2/2re .Why ...
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62 views

Designing a common-emitter amplifier circuit

We are asked to design values for RC, RE, R1, and R2 for the following common-emitter BJT amplifier: It's easy to calculate RE and RC: But I couldn't find a ...
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66 views

Class AB amplifier becomes hotter, using more current and then becoming even hotter

In the circuit above a Class AB amplifier (this is one also called Class A+AB) can be seen with Q1 and Q3 used to get the current biasing voltage for Q2 and Q4. transistors Q2 and Q4 become hotter ...
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39 views

Alternating between two LEDS using BJTs and SPST Switch

I made a circuit based on this post, Alternating between two LEDS using BJTs. It seems to work in the simulation just fine but when I'm connecting it with real components, I get funny behavior. ...
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44 views

Identify this 2xNPN AC-coupled preamplifier circuit

My workmate has this nifty little EMI-detecting wand he built back in 2000. It senses EMI fields using an approx. 200 turn air-core coil, and converts them to audio signal. He uses it to detect e.g. ...
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84 views

Why hFE(DC gain) shown on multimeter isn't equal to the datasheed hFE?

I have a tip122 and discovered my multimeter uses Vce=2,8V DC and Ib=10uA for its hFE test. When I insert the transistor on the terminals for hFE test, the gain on the multimeter alternates between 1 ...
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54 views

Negative base current in Joule Thief

simulate this circuit – Schematic created using CircuitLab My question is regarding the Joule Tief shown below... The graph is from an LTSpice simulation...It seems from the graph that ...
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40 views

Calculating bias resistor with two BJTs

I'm trying to solve for R1 given the following circuit, given Vin=3.3V: Both Q1 and Q2 are ON MMBT3904L, but the datasheet specs are confusing to me. Do I assume the current through R2 is 200mA ...
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Alpha/Beta Parameters of BJT

The BJT Current equations are given as :- IE = IC + IB IC = \$\alpha\$ IE IC = \$\beta\$ IB Does the relations with \$\alpha\$ and \$\beta\$ parameters include the reverse saturation current ...
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47 views

What could be the target applications for these BJTs?

NXP recently introduced a new family of BJTs with switching capabilities of up too 100V, 10A , see "The toughest bipolar transistor - 100 V in LFPAK/Power-SO8". I cannot think of a switching ...
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37 views

What are the benefits of this Class A followed by Class AB instead of just a Class AB amplifier?

In figure 1, there's are two BJTs at the left side in Class A amplifier configuration followed by two BJTs in Class AB amplifier configuration. The two transistors that are added at the left side ...
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28 views

Achieving higher current at the lowside MOSFET to pulse LED

I have attached the following circuits which i have been developing overtime. The OBJECTIVE is to get as high as possible a current at the gate of the MOSFET (VF1) to achieve faster pulse times of ...
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67 views

Intuitive explanation for this hysteresis circuit?

simulate this circuit – Schematic created using CircuitLab I am trying to get an intuitive understanding of this small circuit. I have both breadboarded it to look at behavior on a scope ...
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269 views

A question about Transistor in forward-active biasing?

I have question about transistor biasing. Between picture 1 and 2, what's difference, why we add the resistor RE in pic 2 ? what's it effect to circuit ? Similarity for pics 3 and 4, instead of ...
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87 views

Why are BJT operating modes named the way they are?

I know that a Bipolar Junction Transistor has four operating modes dictated by the base-collector junction and the base emitter junction's biasing: What I can't seem to find is the reasoning behind ...
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23 views

How to use the “Switching characteristics” parameters in the BJT's datasheet

In Fairchild's MMBT4401's datasheet (Note: This is not the newest one from official site, but it seems it contain more information than the newest one, so I use it as an alternative), there are some ...
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78 views

Current mirrors as active loads in BJT differential amplifier, what does that mean?

I have seen current mirrors being used as current source in differential stage of an amplifier design. The reason given is that the current mirror has a very high output impedance and behaves like an ...
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42 views

H Bridge Voltage Drop w/ Motor Installed

first post after searching the net/ site for quite some time. I have this H-Bridge circuit http://www.circuitstoday.com/h-bridge-motor-driver-circuit I'm using 3 AA batteries to test this BEFORE ...
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105 views

BJT - absolute maximum base current?

Let's look at the datasheet for an MMBT3904, just for example. The absolute maximum section talks mostly about maximum voltage differences, and a single current limit - the collector current. I'm ...
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Why are MOSFETs better than BJTs in application of Voltage Controlled Resistor?

Why are MOSFETs better than BJTs in application of Voltage Controlled Resistor ? Thanks for your responses.
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56 views

BJT VCVS with high gain

In a lecture I learnt a BJT VCVS which has gain = 1, i.e a voltage buffer as shown in the figure. The speaker said that it was the ideal VCVS model of a BJT. My question is that is it possible for ...
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what does it mean for a to BJT operating at the edge between the active and saturation modes?

ive recently been fascinated with diodes and was wondering how i'd design a circuit that works at the edge of the breakpoint between the active and saturation mode. How would the circuit be analysed?
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BJT Amplifier in AC mode

In the lesson on BJT Amplifiers, we were told the we can find the AC equivalent circuit by replacing all capacitors by short circuits, inductors (if any) by open circuits, dc voltage sources by ground ...
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FET and BJT transistor question

We have the circuit in the figure BJT transistor has the parameters β=80 and the JFET transistor has the parameters Vp=-4 Volt and Idss=8 mA; Vgs=-2.6 Volt and Ids=1 mA We have R1=470 Kohm ,Rc=3.6 ...
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70 views

What does this symbol represent?

I am trying to understand the internal circuit schematic of the LM565 phase locked loop IC, on page 6 of this datasheet: PDF Datasheet for LM565 from TI website In the upper middle, there is a ...
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48 views

How to remove degradation in voltage gain when replacing the original \$R_L\$ with a small value resistor?

For the following common-emitter amplifier, the original \$R_L = 4.7\space kΩ\$. When I replace it with a small value resistor (\$100\spaceΩ\$), the voltage gain will drop. Is there any way to drive ...
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38 views

Bridging Discrete (BJT) Amp Channels

For my Electronics II class, I designed a discrete BJT amplifier circuit including a VGain, Buffer, and Power stage. I succeeded in meeting the specs, and the next step is to improve our design in ...
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BJT in reverse active mode [duplicate]

I was wondering, what are current directions in reverse active mode? I know that in this mode gain Beta is much smaller than Beta in forward active mode and for BJT to work in thise mode it must be ...
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85 views

BJT in Saturation

Is it possible for the base current to exceed the collector current for a BJT in saturation mode? (If the base current was increased without the collector current increasing at all)
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106 views

why do 2N2222 and PN2222 avalanche differently

i've been experimenting with a 2N2222 transistor (in the TO-18 metal case) and using it as an avalanche transistor -- by not connecting the base and having the emitter and collector connected in ...
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87 views

BJT Switch with a Diode from Base to Emitter

In this circuit, the diode is supposed to force a higher input voltage to turn the LED on, however when I created it on a breadboard I measured about the same input voltage (without the diode) to turn ...
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2k views

Basic transistor questions

I've created the circuit shown. I'm using a 9V battery (actually throwing out 9.53V) and 5V coming from an Arduino to test with both 9 and 5 volts. The transistor is a BC 548B (datasheet I'm using is ...
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Complex circuit analysis

I need help solving the circuit above. I don't understand how to analyse the op amp using the small signal model in order to calculate the Vout/V3, the input resistance (Rin) and output resistance ...
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109 views

Output Impedance of BJT/Mosfet amplifiers

I have heard in lectures that the desired output impedance for the BJT/Mosfet Amplifiers is LOW. But these transistors are Transconductance amplifiers 'by birth'. I mean they give output current ...
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87 views

Square wave into emitter follower

I put a square wave of relatively low rise and fall time (of about 10ns), and wanted to see the response from an emitter follower output. I put together the circuit and here's what I see on scope. ...
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65 views

What are the limitations of the Ebers-Moll model of the BJT

The Ebers-Moll model is considered simple yet effective model of the BJT. What makes it special and when does it break down i.e is not applicable?