Questions tagged [darlington]

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

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2answers
72 views

Which one would be better for 3.3V outputs among ULN2001 and ULN2003?

I intend on driving 24VDC relays with darlington arrays of the ULN200X series. Since the darlingtons will be driven by a 3.3VDC outputs I am hesitating on whether I should choose ULN2003 or ULN2001. ...
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112 views

H Bridge failing under load

I have made 2 H bridges following this schematic. I have replaced TIP107 with TIP147 TIP102 with TIP142 The Opto-couplers are P785. I have not included the diodes as they are internal to the TIP. I am ...
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1answer
70 views

Making a Darlington transistor (eg: TIP120) with D882 to drive 12V LEDs with 3.3V or 5V input RPi

I am getting into circuits and trying to improve my knowledge but even though it might sound like a silly question but here is my story short: What I am trying to do I am building a circuit to drive ...
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1answer
43 views

Touch switch for hanging lamp (touching metal bar): Ideas?

A few years ago, we have bought an IKEA Glimt hanging lamp that operates with halogen lamps. It has a "touch dim" functionality, so when a person touches the metal bar of the lamp, it dims (...
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2answers
77 views

Darlington biasing design error in a commercial frequency counter oven control circuit?

I am repairing a commercial frequency counter (brand to remain anonymous) that had the crystal oven visibly overheat. There is a small PCB in the oven that holds the crystals, the oscillator circuit, ...
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1answer
326 views

How to power WeMos D1 Mini without USB?

The title does not tell the entire story. I have successfully powered my WeMos by supplying 5vdc to the 5v pin. My power source is 12v battery so I am using a buck converter to drop the voltage to 5v. ...
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3answers
135 views

One transistor versus two transistors as a switch

Why does the led dim first and then switch off when I use one transistor as a switch, but directly switch off when I use two transistors as a switch? These are the two circuits:
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0answers
51 views

AC current gain of an emitter follower configuration with a Darlington transistor and a source resistance

We're using the book Electronic Devices and Circuit Theory by Boylestad for our circuits class and are currently on Darlington transistors. I'm trying to solve the current gain of a circuit with an ...
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2answers
79 views

why could Darlington circuit protect Load Dump at automotive?

I just took over a project from EX co-worker and not understand a circuit (Darlington circuit) designed to against load dump(5b) at automotive. in my previous experience, TVS usually is used for ...
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4answers
137 views

Classic multivibrator circuit and LTSpice, why is there reverse voltage on base even with diode?

I had fun today learning the basics of LTSpice using a variation of the "classic multivibrator" (*). I have also built a working version with real components. There is a significant ...
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1answer
51 views

Resistor value calculation for optocoupler input

I am working on an optocoupler (LTV-845) circuit. Below is my working circuit: Forward current flowing to opto input would be (Vcc-Vf(LED)) / Rf = (24V-2.1V)/470 = 0.046A. Is my understanding correct?...
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1answer
96 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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47 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
73 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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38 views

problem in programming ISR in 8051

in this code : ...
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1answer
61 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
67 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
32 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
125 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
152 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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92 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
84 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
158 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
72 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
497 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
92 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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573 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
56 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
415 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
50 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
374 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
75 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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55 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
50 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
47 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
569 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
1k 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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53 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
501 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
120 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
85 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
187 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
98 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
215 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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178 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
179 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
320 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
669 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
606 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
578 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 ...