Electrical Engineering

Questions tagged [darlington]

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A structure containing two of the same BJT, used for its increased current gain compared to a single BJT.

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86 views

Strange floating base NPN behavior

I'm learning about NPN transistors and have wired up this: I understand some of its behavior, but one is a complete mystery for me. First, if I tie "B" (green dangling wire) to "G"...
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40 views

Problem in 5v pump

I connected the pump to tip122 darlington transistor to control it via serial port. but the pump doesn't work. instead , it makes sound. how can i make the pump work the circuit of the tip122 : the ...
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1answer
68 views

How to solve this Darlington circuit

So I have this circuit; it should be a Darlington transistor circuit and I need to find the bias point for it. simulate this circuit – Schematic created using CircuitLab https://imgur.com/...
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36 views

problem in programming ISR in 8051

in this code : ...
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1answer
60 views

Identifying transistors

I have found an old driver board (probably the mid 80's) for stepper motors (rated at 1.25V 3.8A) and I want to rebuild the H-Bridge using the parts on the board and a micro-controller as an input. I ...
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1answer
60 views

Complementary pair - Role of capacitor on emitter

I bought this little kit for a class AB amplifier. The second stage is quite clear (and typical), but I am struggling to understand the role of capacitor C2 on the emitter branch in the first stage. ...
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1answer
30 views

Connecting many electromagnets with polarity control

I'm trying to see if it's possible to build a large grid (hundreds) of electromagnets, where very electromagnet should be able to get both directions of currents (to generate magnetic fields with both ...
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1answer
78 views

Need guidance for building a electronic load using BJTs

I've been studying DC electronic loads and almost all of them used mosfet as main transistor, while researching I find out that mosfets that are designed to work in their linear region are expensive ...
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2answers
65 views

Feedback schematic/pcb 16 channel relay wifi module

I have a few questions about a 16 channel relay module I designed, maybe someone can help me. Generally this consists of a ESP-12F, two I2C IO Expander, two darlington array ICs to drive 16x 5V relays....
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2answers
87 views

How to prove that \$I_3=Vi/R1\$ in a darlingtonpair circuit with opamp when \$\beta_2\to\infty\$? [closed]

I have the following circuit: simulate this circuit – Schematic created using CircuitLab How can I prove that \$I_3=Vi/R1\$ when \$\beta_2\to\infty\$?
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1answer
64 views

Regarding Darlington pair problem

I tried to do the steps... Ie = 1.98/100 = 0.0198A Beta for 1st transistor and 2nd one is 2 So total current gain= (beta1 +1)(beta2 +1) Ie/Ib = 3*3= 9 Ib= 0.0198/9 =2.2mA But answers are not matching.....
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1answer
94 views

Why does a Darlington pair have a higher input impedance compared to a regular normal BJT transistor?

Freshman here, and I've been searching for an answer to this question, but I could not find any actual justifications yet. Basically, I am studying the concepts of a Darlington circuit, and saw that ...
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1answer
63 views

Darlington transistor for driving coils

I try to drive two small pcb coils. The coils have a resistance of around 14 Ohms (i dont know the L value). I have a PIC10F200 controlling the base of a BCV27. However i dont seem to get much more ...
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2answers
231 views

How to add CC/CV feature with single LM358 for variable linear power supply?

I have a few weeks with a problem in the design of my bench power supply. First of all I have this design from this guy on YouTube https://youtu.be/_CFIovMkRyg that made a variable power supply using ...
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1answer
55 views

Use of clamp diode in ULN2003A

I'm planning to use a ULN2003A 7-channel Darlington driver (datasheet) to control 4 to 7 LEDs in common-anode configuration from a Teensy MCU: (The "trident" is a common-anode RGB LED). The ...
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240 views

Best power transistor for a high PWM output from ESP32

I need your advice whether to use a Tip122 Darlington transistor or a BD137 medium-power transistor Or a IRL3705 MOSFET to drive 10 Parallel infrared LEDs. Each LED has a forward voltage of almost 1.2-...
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1answer
46 views

AM circuit LTspice

I have to analyze the following circuit and understand its function. As far as I understand the top part is the simple phase-shift oscillator generating output sine wave at circa 145kHz. The NE555 is ...
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2answers
229 views

How to drive high voltage transistor with low voltage op amp?

I'm trying to drive a darlington pair with 24 V collector voltage with an low voltage op amp. I tried adding a PNP transistor so the op amp just have to drive that single transistor, but haven't had ...
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2answers
43 views

ULN2803 behavior when its output is not connected to any load in this circuit?

I'm studying the a circuit that is using a driver ULN2803 datashet. The driver is needed for external loads as LEDs when a pin is writing. The situation that I would like to talk about is when the pin ...
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2answers
302 views

How does my breadboard circuit diagram look? Is my circuit going to explode?

I'm working on my first Arduino project and I thought I picked something simple enough. But before I set my breadboard on fire or ruin any of my components, I wanted to make sure my plan made since ...
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1answer
57 views

Explanation for parallel darlington behavior

I've built and simulated the circuit below in real life, LTSpice and Stack-Echange-Spice. It behaves in a similar fashion in all of these Environments. When the "LAMP2" load is disconnected, the Base ...
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53 views

Darlington transistors killing the output

I was trying to recreate a subwoofer following this website. And the first 2 stages function as expected. The low pass filter is working which i verified , and the the second stage amplifies the peak ...
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1answer
45 views

How do these phototransistors circuits work?

In the figure 1, When there is insufficient light, the darlington transistor is biased on, keeping the relay energized. When there is sufficient light, phototransistor FT turns on; I imagine this ...
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2answers
39 views

Convert 8 bit Parallel output from ULN2003 to serial without any Microcontroller

I am hobbyist only with some basic idea about electronics.. I am trying to measure rooftop watertank water level and to display it on a small led bargraph. So by googling I thought about to proceed ...
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1answer
237 views

Multisim vs LTspice : Different Result

I was using the simple darlington circuit below as the test circuit. DC operating point analysis was run on both LTspice and Multisim, with V2 as the manipulating variable and the base voltage of Q2 ...
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1answer
399 views

Input impedance for a darlington pair

I want to calculate the input impedance when I am using a Darlington pair and I'm getting a little confused on the appropriate equation to use. In Electronic Devices by Floyd he gives and example of ...
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47 views

Darlington transistor heats up : regulating transformer output

I am in great need of a 12v DC transformer. So I built one using some components I have lying around: the case of the transformer I have says ...
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1answer
344 views

What advantages does the Darlington pair have over the Sziklai pair?

With all the free time I've had lately due to current events, I've found myself looking into analog amplifier design and analysis (if it helps provide context, my area of expertise is power ...
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2answers
84 views

How fast will a resistor heat up under high power?

I am building a circuit for some induction coils on a coilgun, and it will draw about 1.75A from a 12V power source (I know it probably won't be very powerful, but it is difficult to find resistors ...
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1answer
80 views

Biasing a emitter follower darlington configuration

Below picture is a simple voltage regulator(link to simulator): The current at the op amps output is at nA region(why?), how can I increase the current at the op amps output without adding a third ...
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4answers
101 views

Determine if a heatsink is required (Darlington TIP120)

I'm planning to switch 1A load at 5V with a TIP120. Looking at it's power derating graph I see that at 5W case can be around 140C, but how can I tell if it will get hotter than that? In the ...
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6answers
90 views

Way to show that the current through a Darlington pair is determined by the emitter resistor

I have the following circuit: simulate this circuit – Schematic created using CircuitLab Is there a way to show that the current through \$\text{R}_1\$ is given by \$\text{V}_\text{i}/\text{R}...
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2answers
109 views

Requirement of ULN2003 IC in circuit

I'm just a hobbyist and actually from software side. Trying to build a simple water level indicator and found the following circuit using the IC ULN2003. But due to my very less knowledge I'm not ...
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135 views

ULN2803 relay driver working for high loads

I am trying to understand the working of this Darlington transistor array. I am using it for inductive loads and for driving the loads of my relays, but now I am trying to understand the part of its ...
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1answer
139 views

Why are there three transistor pairs in Class B Power Amplifier circuit?

I have a Class B amplifier circuit to be done in lab. Why three pair of transistors are used in this? I suppose one is a Darlington pair but what is the requirement of the third one. Also, why there ...
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4answers
246 views

What's wrong with this PWM-controlled constant current sink?

T10 gets very hot and starts melting within 30s, even with a heat sink and values way below its rated 15A. Edit: I know it is not a true PWM controlled constant current, but that what I can do with ...
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1answer
629 views

Current mirror: is there a name for this NPN-PNP pair, and how does it work?

I'm looking at the schematic for the MC1460 voltage regulator. At the top it has three current mirrors, each with an NPN-PNP pair. Is there a name for that transistor structure? These pairs look like ...
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3answers
467 views

Darlington as CB

Why do we use Darlington pair? I've heard that we don't use it as common base. Why is that? Why don't we just develop a BJT with high beta value istead of using this structure? What are the different ...
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4answers
306 views

What is an open collector?

I am new to electronics, and I'm reading a book on embedded systems and bumped into an "Open Collector". I know that a transistor has a base, which acts like a switch for the current to flow from ...
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1answer
180 views

DC analysis of Darlington pair

So I'm having this darlington pair here I'm doing DC analysis of this darlington pair Can anyone explain why is R2 is 6.58, shouldn't it be aprx 7.39?
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1answer
163 views

How does a darlington pair work?

How does a darlington pair work? I am curious about how the second transistor sustains the current Ie of the first transistor. Why is the base not damaged despite ...
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125 views

Is it necessary to opto-isolate a darlington array output?

I've got the following circuit going: A Vishay opto-isolator (CNY74-4) that takes input from buttons that work on 24V, and outputs to microcontroller pins (an Olimex ESP32-PoE-ISO in my case). A ...
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1answer
56 views

How must be the pull up resistor circuit connected to the driver input?

I have this circuit for getting 12V or 0V from external control signals. Signals will arrive by pin connector to my board. Switches will also be out of this board. External control signal could be ...
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3answers
134 views

Output stage using 2 transistors

I want to understand how does this 2-transistor circuit work. It is used in a schematic for increasing the current rating at the discrete output stage. This does not look like a standard darlington ...
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3answers
262 views

Darlington array: How to output desired voltage at uln2803a driver colectors?

Someone suggested this driver array to get the current I need: datasheet I also need a 12V signal and about a current of 100mA in order to control a relay coil. My 12V signal would come from a logic ...
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1answer
53 views

Multiple Lamp indicators and LED driving using TPL7407LA simultaneously

I am using TPL7407LA for driver circuit, it will be getting inputs from pic18f67k40 and driving multiple Lamp indicators(24v) and multiple LED indicators(12v). My question is : Is it possible to ...
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1answer
74 views

Determine total current in a darlington transistor

I'm trying to figure out what will be the total current consumption of a TIP120. Looking at the internal schematic I see that the second BJT's base is following the emitter of the first one so it ...
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3answers
447 views

ULQ2003 not driving a Relay properly

I am driving a 9V DC (5 PINS) Relay from darlington array ULQ2003. The ULQ2003 COM pin is connected to 9V power supply while the Relay coil is connected to +12V supply. The Ground of both are ...
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1answer
1k views

What is this triple-transistor arrangement called?

For an old Fuji 2DI200D-100 power transistor module, it uses three transistors internally for each half-bridge: The circuit in question doesn't connect to the middle bases at all, just B1 and B2, so ...
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2answers
306 views

Complementary transistor pair with a bipolar transistor and a MOSFET

I own a set of Soviet IN-14 Nixie tubes and I would like to use them to make a vintage clock. I found this example schematic of a "Nixie clock": I don't understand what is the purpose of using a ...

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