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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Comparing sensitivity to temperature changes of BJT (transistor) circuits in Common Emitter Configuration

I measured Ic variation with Ib when Vce = 15v kept constant for BJT (NPN) in Common Emitter config and also BJT Common Emitter config with series 47 Ohm resistor connected. From the experiment I ...
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58 views

BJT Transistor Biasing

For normal operation it is said to remember: Emmitter Base junction is always forward biased Collector Base junction is always reverse biased Can someone explain to me what this means? My view is ...
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131 views

How to increase the current in this circuit?

Im trying to build a circuit to send information using IR led, using pulse signals (Im trying to mimic a home appliance remote control). My leds (datasheet) operate at 1.3V, and their maximum pulse ...
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14 views

Driving 3V motor, BDX53C

Briefing: Trying to drive a 3V motor with gearbox, using TM4C. Motor specs are given below. First tried with 2N2222A, later plugged motor directly in to LF33ABV voltage regulator. On both setups, ...
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120 views

Which is the objective of an Base-emitter resistor?

Can someone explain me the purpose of the resistor R2? If I remove R2, the circuit will perform the same result, won't it? simulate this circuit – Schematic created using CircuitLab
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What does the beta factor do here? (current mirror) [closed]

I'm reading through a textbook reference and came across a problem I don't understand how to solve: For the circuit shown in Figure, IA = 3 mA and VCE = 5.4 V. If all transistors have the same ...
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83 views

Need help in biasing TIP31 in common collector mode- edited

I am using an Arduino Uno board and R-2R DAC to obtain a signal which should vibrate a transducer connected across RL of common collector amplifier using TIP31C. I need around 300mA of current to ...
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37 views

Missing Bipolar Definition for “PNP”

I've been making a schematic diagram for an LDO which has a 'Vref' subcircuit which contains 4 PNP bjt's. Now when I run the schematic to produce a netlist, a fatal error (image shown) occured. How ...
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57 views

Calculating resistance to make BJT transistor act as a switch

Let's say you're given a circuit diagram as follows: I want to find R1 and R2 so that forward voltage drop across the LED is 2V with an overdrive factor of at least 2. Current of 25mA from a ...
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50 views

Output impedance of differential amplifier

How do I calculate output impedance of the following differential amplifier? Input are at the base of two BJTs. I know that it's Rc || resistance looking into the collector of Q2, but how to find ...
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48 views

Class AB Amplifier Frequency Response

I have designed an AB Audio Amplifier, but even though the gain is acceptable, the frequency response is terrible.As seen in the schematic, there is a feedback/preamplifer stage and an output stage, I ...
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73 views

Transistors: Explain the key differences between SMALL and LARGE-signal analysis

I'm in an electronics class and I feel like this portion of the lecture was covered in a vague manner. I'm not really sure what the purpose of doing either a large or small signal analysis is, and ...
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30 views

What is the significance of Input Resistance and Output Resistance in CE,CC,CB amplifiers?

Common Emitter, Common Collector and Common Base amplifiers have their specific purpose with differing voltage/current gains. For example, I know for a common collector has a voltage gain of ...
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40 views

Design a tuned common emitter amplifier

I'm getting stuck at the problem 2.16 in Art of Electronics. "Design a tuned common emitter amplifier stage to operate at 100kHz. Use a bypassed emitter resistor, and set the quiescent current at ...
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2answers
58 views

No Miller effect in differential amplifiers

Why is there no Miller effect in differential amplifier and cascode circuits? (from the book Art of Electronics)
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46 views

Finding relevant voltages and current in a BJT

I'm supposed to find Vb, Ve, Ic, Vc and Vce for this circuit but I have never seen anything like this, so I'm lost on how to even approach it. Do I start from KVL and write two loops? But then ...
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43 views

KVL in a BJT circuit

I'm having a lot of trouble understanding how KVL is applied in a BJT circuit. Here's an example circuit diagram: Assume I want to get Vc, so I think to myself that I must add up all the voltages ...
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57 views

How to drive a capacitor from an AC current source

I am wondering how it is possible to drive a constant ac current through a capacitor. I would like to use a transistor as the current source/sink. The problem is that if I put the capacitor in the ...
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2answers
77 views

Newbie question - sawtooth signal generation - capacitor discharge via bjt

I'm trying to realize a sawtooth wave generator. The circuit is composed by an op-amp integrator which creates the ramp. Then the integrator output is chained to a comparator with a fixed threshold, ...
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75 views

How does this signal inverter works?

I am trying to wrap my head around the circuit mentioned in the accepted answer to this post. It looks like a fairly simple deal except for the part where I wonder what is keeping the signal to LOW ...
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56 views

BJT short circuit failure cause in switch application

i read in this discussion about the FET short circuit causes. But I want to know what leads to BJT short-circuit ?
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Why does FZT653 a SMT BJT device have 2 collectors?

The FZT653 in SOT223 package has 3 normal terminals at the bottom, collector, emitter, base. However, it also has a collector on the top. Why is this so? Which is the real collector.
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BJT Forward Active

Regarding BJT, forward active mode of operation i don't seem to get something. I will use NPN type. In the forward active regime, Vbe>= 0.75 V, so electrons flow from the emitter through the base .Ok, ...
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How to add a multi-emitter BJT to LTSpice?

I want to simulate the standard TTL NAND gate which contains a multi-emitter BJT transistor in LTSpice. I've searched the components available in LTSpice but didn't found this component. How can I add ...
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42 views

Need 300mA current to drive a transducer

I am working on a project in which I need to use a preloaded value to vibrate a transducer. So loaded required values into Arduino Uno, converted into analog values using R-2R DAC and buffered values ...
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82 views

A question on voltage divider resistances used in BJT biasing

I'm reading a text on BJT common collector amplifier biasing. Text says: The voltage divider (R1 and R2) is used to give the input signal (after passing through the capacitor) a positive dc ...
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Tips on analyzing circuit with multiple op-amps and bjts

In a homework exercise I need to sketch the Vout-vs-Vin graph, having it first obtained analytically. I know that Ur and Vin are both nonnegative, and the circuit is shown here: It seems like there ...
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64 views

The relationship between \$\beta\$ and \$I_C\$, \$V_{CE}\$

It was pointed out to me recently that I don't have a good understanding of the varying relationship between a BJT's \$\beta\$ parameter (or \$h_{FE}\$) and the operating point of the transistor. ...
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167 views

Effect of BJT common emitter amplifier resistor(Rc,Re) ratios? How to select it?

Above is a part of a BJT common emitter amplifier with 15V Vcc(all caps ignored for DC). I was following a tutorial which explains how to setup parameters step by step. When explaining the DC ...
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65 views

Transistor bias circuit

How can I find the base current of this circuit. I was trying to find \$\beta \$ from \$(\beta+1)I_B = I_E \$. where \$V_{BE}=0.7V, I_E=0.5mA\$ simulate this circuit – Schematic created ...
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113 views

Controlling higher voltage and load via high-side switch from a microcontroller

I am building a battery-powered uC circuit with an RGB LED. The LED is common cathode, so the circuit for switching the LED elements has to be high-side. The LED is a higher-current LED, so it cannot ...
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29 views

Influential factors setting the operation point of a bipolar transistor?

I do know why and where we should set the operation point of a transistor. We also learned calculations during lecture. However I do not know, what values do we change to set the Ib DC current. Are we ...
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Raspberry pi B+ internal power supply ckt?

I have just started to study about raspberry pi B+ (data sheet) Can somebody explain the working of power supply circuit (individual component wise) starting from pg 14. How and why it is ...
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27 views

Could someone explain attached M-bus master circuit?

Could someone explain attached m-bus bjt circuit in details? Is this a repeater of some sort?
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54 views

Working principles of an LDR Light Switch

This is a simple circuit which dims the LED according to the light recieved by the LDR or simply a light switch. Can anybody explain how two BJTs opearete in the circuit, or simply how the system ...
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67 views

Analyzing BJT differential pair with feedback

I have an exam next week, and I need to get a real high mark to pass. Therefore I'm looking for some hard questions to solve, and this is one. While I don't expect a full solution from you here, ...
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121 views

Why is the Collector current of a BJT transistor independent of the Collector Base voltage?

Ignoring the modulation of the effective base width, why is the collector current independent of the reverse bias voltage across the Base-Collector P-N junction? On one hand, it is easy to see that ...
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Forced beta too small

Let's take an example in which the recommended beta for a transistor's(NPN) saturation is 10.If you use a forced beta smaller than 10,will the transistor still be saturated succesfully?Can hFE be ...
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BJT characteristic curves — generating them

I know that the relationship between the base current \$i_B\$ and the base-emitter voltage \$v_{BE}\$ is given by the Shockley equation. \$i_B = I_S (e^{v_{BE} / V_T} - 1)\$ This is the input ...
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55 views

How is the solution for \$\alpha\$ and \$\beta\$ current gain of a BJT derived?

I'm just an enthusiast, and not too good at maths; I'm exploring constant current source circuits, in doing so I came across two equations for BJT current gain: Could someone help me understand how ...
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70 views

BJT Saturation with small load/ H-bridge

I am trying to analyze the operation of a BJT H-bridge configuration. I have searched through these forums and Google and can't seem to find an answer to my question. It is my understanding that it ...
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Why would the transistor not switch?

I was reading an example from a text book. And for this circuit above the author claims when R3 is less than 100 ohm Q3 will not switch. I couldn't figure out the "reason" why. But I verified with ...
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108 views

Powering LEDs with a transistor

I'm a beginner. I'm designing a battery powered LED flashlight with a dimmer. The flashlight will have 3 LEDs and the dimmer will be controlled by a PWM signal generated by a 555. The circuit is ...
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26 views

Function Generator Driving Multiple Outputs

I am characterizing a solenoid (valve) and I am using a function generator as the control signal on a BJT to turn on/off the solenoid. I can generate the pulses I need but I need the same control ...
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1answer
37 views

LTspice `Icrating` of BJTs

I see LTspice has an Icrating parameter for BJTs. As far as I can tell this isn't part of SGP (SPICE Gummel-Poon model) and also not present in other flavors of ...
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342 views

Why am I getting negative base current in LTSpice simulation?

When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in ...
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61 views

How to analyze BJT amp circuit with multiple gains

Im currently trying to solve this problem for total gain, though I'm stuck right off the bat with DC analysis. I was told the emitter current for Q1 and Q2 will be 0.9 mA though I have no idea why. ...
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Why should collector voltage need to be higher than emitter voltage? [duplicate]

I'm reading up on npn (and by extension pnp) transistors, and I got tripped up on a note from my book (Practical Electronics for Inventors, 3rd edition, p. 433) "For an npn transistor, the voltage at ...
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Help me to understand this schematic

I found 220V AC to 12V DC - 30A power supply schematic: My question is, where Ib1 current goes (where base pin is connected)? Edit: Here is one more schematic with same strange base pin ...
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84 views

How is FM modulation is achieved using a single BJT

I want to understand how this circuit achieve frequency modulation. The BJT is a 2N3904. I found that millers effect comes into play and varies the frequency of the tank circuit about a center ...