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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Curret mirror with discrete BJTs?

I need to supply power for some power diodes. The power supply units are current regulated, the diodes are connected in series. Let's say that i hve 3 strips of leds, each one needs 400mA, around 20V ...
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Biasing a common collector

How do I bias a common collector to secure maximum output swing WITHOUT using a resistive divider? How can I use my transistor as a voltage source with output about half my Vcc?
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Bipolar Junction Transistors

If the switching frequency is increased for BJT what happens to the power dissipation? Will it increase, decrease, or remains the same and whats the logical reason for it?
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Deriving current gain and voltage gain for common base BJT

For a common base configuration BJT such as the one shown here: http://i.imgur.com/M9LtHoW.png How can I derive the voltage gain and current gain? I found the answer on Wikipedia but all my attempts ...
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Question on DC analysis of BJT - Common Base

I'm trying to solve a question from my book. The answer for the question is given but I keep getting a different answer. I don't know if I'm doing it the wrong way or the book is wrong. This is the ...
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56 views

Can you find an analytic expression for the (beta)hfe of a BJT?

I understand there are two models \$Ic=\beta Ib\$ and \$Ic=I_s exp (\frac{V_{BE}}{Vt})\$ for a bipolar junction transistor. However (correct me if I am wrong), I have not seen any textbook ...
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Using PNP instead of NPN merely requires one to make circuit upside down and reverse current direction, why do we not just use one of the two types?

Using PNP instead of NPN merely requires one to make circuit upside down and reverse current direction, if this is true then why don't we just do everything with NPN transistors? Are there any ...
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Detecting electrons as they tunnel through the band gap of a P-N junction

As a learning exercise I'd like to try creating a random number generator using reverse-biased BJTs. As I understand it, if the emitter is saturated in reverse bias, occasionally electrons will ...
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How to Find value of Early voltage of output characteristic curve of BJT?

I have this graph from data that I have. This is the output characteristic curve of BJT. I want to find the value of early voltage VA?
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123 views

How does one approach designing an amplifier using BJTs to drive an 8 ohm speaker?

For a lab class we were assigned a final project where we have to design an amplifier using BJTs, diodes, and capacitors (MOSFETs are not allowed) in order to drive an 8-ohm speaker. The requirements ...
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43 views

BJT pre-biased arrays slower than discrete?

I've got a circuit that works - it's job is to convert a TTL square wave into a +/- 12 volt square wave. simulate this circuit – Schematic created using CircuitLab Note that the ...
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23 views

Finding the DC operating point of this circuit

I'm trying to find the dc operating point of this circuit, it is given that: \$V_{BE_{ON}} = 0.7v\$, \$\beta = 100\$, \$I_{DSS} = 10mA\$ , \$V_P = -2v\$ and also that \$V_A = 1.8v\$. Here is what I ...
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127 views

LEDs driver circuit

I was wondering what is the role of this type of circuit connected to LEDs. I found it in a LED torch supplied by 2xAA batteries. Is it an oscillator? Is it only an energy trick? What are the ...
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37 views

Driving an optoisolator with a 2N2222?

I'm driving an opto-isolated MOSFET gate driver with a 2n2222 transistor from a 3.3V microcontroller (TI Tiva C, 2-8mA max per pin). The IX3108G that I selected needs 10-16mA to be driven ON. This ...
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84 views

Can I alter this circuit?

I am making the following solar charge controller circuit based off of the NE555: This is the webpage I got the schematic from: http://mdpub.com/555Controller/ The potentiometers at the trigger ...
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365 views

Why does current flow into the transistor in a current shunt monitor?

I'm looking at the basic operation of a current shunt monitor*, but I don't quite understand the 'operation' description given by it's manufacturer. Figure 1 shows the basic circuit diagram for ...
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50 views

Explain this exercise to me?

We have the CM half circuit in the figure. I understand that $$A_\text{cm}=\frac{(\alpha\times R_\text{c})}{(2R_\text{e}+ 2re) }$$ but how is this equal to $$\frac{2}{8.65} $$ like it's solved in ...
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52 views

Finding the input resistance of an NPN transistor

The question is asking to find the input resistance of the circuit shown in the picture. R_in "starting" position is shown as well. I have done quite a few problems involving replacing the ...
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93 views

Will there still be small voltage in transistor OFF state?

In Bipolar junction NPN transistor which has three legs as shown below: Case 1: If this transistor is in OFF state i.e. collector is connected to +Vcc and Base is connected to insufficient voltage ...
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44 views

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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45 views

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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109 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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241 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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54 views

NPN BJT used for DC Switching Load [closed]

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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48 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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49 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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61 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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20 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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173 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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77 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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80 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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109 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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41 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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76 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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71 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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61 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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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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99 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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58 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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43 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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52 views

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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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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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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74 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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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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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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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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115 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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63 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 ...