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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PNP TIP126 transistor hot to touch while in use

I have a 7-segment mechanical 'vane' display andbgot it working using a circuit originally suggested to me here. The diagram below is a slightly modified version. Each vane draws around 0.2A of ...
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I made a darlington transistor in LTspice. But, that has different values from theoretical values

As you may see from title, I made a darlington transistor like this. I set each transistor(Q1 and Q2) to have β = 150. So, total darlington β must have 22500 or thereabouts according to a formula ...
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Is this TIP102 Darlington Transistor Circuit Correct?

Objective: Power on Pi Zero by setting pin 13 of Arduino to HIGH. I plan on using the Arduino to measure the Li Ion battery voltage and, if well charged (so, say over 4V), then it will pull pin 13 ...
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Darlington triplet - static electricity detector?

simulate this circuit – Schematic created using CircuitLab I built this circuit. Different versions of this exist on the internet, some using an MPF-102 JFET instead of the 3 NPNs. The various ...
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6 votes
1 answer
354 views

Darlington Triplet

I was playing around in Falstad Circuit Simulator with powering a 2.5V incandescent lamp with a Darlington Triplet. I tried it two different ways and got slightly different results. I'm not sure if ...
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Switching 3.3V 150mA efficiently

I have a load (from 20 LEDs with 20 resistors) that I want to switch on/off as a single block, using a GPIO pin from a micro-controller. I have measured the current to be 145mA at 3.3V Vcc. simulate ...
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Darlington Transistor hybrid parameters from BJT h-parameters

I'm trying to analyze the Darlington transistor model, so I need to calculate the hybrid parameters for this circuit. For example $$h_{ie} = \frac{v_{be}}{i_b}\bigg\rvert_{v_{ce=0}}$$ So which is the ...
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What does a Darlington pair do in a DC power supply circuit?

I really don't understand the role of the Darlington pair (T1) in this circuit. As it is a DC power supply circuit, I always thought that the pair is useful to have a high gain in audio and AOP ...
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37 votes
4 answers
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What is this unusual NPN-PNP transistor pair?

I was looking for the datasheet for a transistor I'd discovered during some reverse engineering, a DK52T. Unfortunately I can't find its datasheet, but I found one for the DK52D. See the image below; ...
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How to set loading(resistance) when i try to simulation Darlington pair limit current between Voltage 9 to 36

How do I set my loading (R13) value for simulating Darlington limit current between 9 to 36 V? If there is no loading (R13), the result of Q1 current (C to E) would not show correctly, but a placing ...
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How does a Zener diode and NPN BJT control circuit provide current limit or thermal shutdown via an NPN Darlington pass transistor?

Background Application: 1995 Ford Ranger Manual Control Blend Door Actuator This 1 page pdf guide shows the block level function of a manual blend door actuator (my component is from a Ford Ranger.) ...
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Unused pins of FMBA14

I am using NPN Darlington array FMBA14. I am only using B1,C1 and E1 pins for my application. The other pins B2,C2 and E2 can be left floating?. Can someone suggest anything on this? Thank you
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230 views

Replacing Darlington with MOSFET for capacitive discharge circuit into a solenoid?

I have the following circuit and criteria and am wondering if it makes sense to replace the Darlington transistor with a MOSFET, and if so how would that change the circuit? This circuit turns on T1 ...
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Have I understood transistors correctly?

These are what I know and what I've concluded about transistors. Correct me if I'm wrong: It's all about current. When we have a determined voltage differential source, BJTs are used to boost the ...
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Simple question about Darlington BJT

I have this circuit for a pasive balancing battery cell with 2 PNP Darlington transistors with switching role. When I close the circuit with the optocoupler the transistors are open. R7 and R1 are ...
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3 votes
2 answers
681 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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5 votes
2 answers
196 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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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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1 answer
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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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4 votes
2 answers
96 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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1 vote
1 answer
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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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2 votes
3 answers
273 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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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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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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2 votes
4 answers
263 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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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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3 votes
1 answer
121 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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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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-1 votes
1 answer
85 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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42 views

problem in programming ISR in 8051

in this code : ...
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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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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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1 answer
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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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1 vote
1 answer
299 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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1 vote
2 answers
551 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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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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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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1 vote
1 answer
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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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1 vote
1 answer
78 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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3 votes
2 answers
1k 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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2 votes
1 answer
189 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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0 votes
2 answers
1k 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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0 votes
1 answer
67 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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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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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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2 votes
2 answers
526 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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1 answer
176 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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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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2 answers
87 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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1 answer
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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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