Questions tagged [darlington]
A structure containing two of the same BJT, used for its increased current gain compared to a single BJT.
186
questions
2
votes
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.
...
3
votes
2answers
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 ...
1
vote
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 ...
1
vote
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 (...
4
votes
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, ...
1
vote
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. ...
2
votes
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:
0
votes
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 ...
0
votes
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 ...
2
votes
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 ...
0
votes
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?...
3
votes
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"...
0
votes
0answers
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 ...
-1
votes
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/...
0
votes
0answers
38 views
0
votes
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 ...
0
votes
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. ...
1
vote
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 ...
0
votes
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 ...
1
vote
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....
0
votes
2answers
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\$?
1
vote
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.....
1
vote
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 ...
1
vote
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 ...
3
votes
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 ...
1
vote
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 ...
0
votes
2answers
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-...
0
votes
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 ...
1
vote
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 ...
0
votes
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 ...
3
votes
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
2
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
1
vote
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}...
0
votes
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 ...
0
votes
0answers
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 ...
2
votes
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 ...
0
votes
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 ...
3
votes
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 ...
0
votes
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 ...
2
votes
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 ...
