Questions tagged [current-limiting]

Current limiting is the practice in electrical or electronic circuits of imposing an upper limit on the current that may be delivered to a load with the purpose of protecting the circuit generating or transmitting the current from harmful effects due to a short-circuit or similar problem in the load.

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Correct formula for LED current-limiting resistor?

I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is: $$ R = \frac{V_{cc} - V_f}{I_f} $$ Seems logical, and makes complete sense. The answers to the ...
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Solution for adapting to USB current draw limits?

Summary: I'm setting up a USB-powered Li-ion charging circuit and would of course like to draw the maximum charge current possible situationally -- but also want to ensure I don't violate the USB ...
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Are there still practical modern uses for large through-hole resistors?

When teaching electronics to college students, we often use these large 1 W cylindrical resistors - not because we need the wattage rating, but because they are easy to handle and read the color code ...
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17 votes
7 answers
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P-channel MOSFET inrush current limiting

I have been searching EESE and Google for several weeks now for a solution to this problem, and while I found some proposals that seemed promising, the real-world implementation fell short of ...
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Does an over voltage, over current and reverse polarity protection IC exist?

I'm designing a circuit that has the following protection requirements: Reverse polarity Over voltage (60v max) Over current (approx 1A) There's quite a large input voltage range, 10v to 60v. 48v ...
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14 votes
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Why does this optocoupler's datasheet recommend splitting a current limiting resistor in two?

And not only that, they also want to keep a ratio of R1/R2=1.5 The opto in question is ACPL-M21L by Broadcom Here's a link to the datasheet: https://docs.broadcom.com/docs/AV02-3462EN Thanks.
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5 answers
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Is it recommended to set the current limit on a bench power supply by shorting it?

I have a Rapid 85-1901 switching mode 0-20V 0-5A bench power supply: Without a load attached the current shows 0A no matter how you turn the dial. After searching how to set the current limit online, ...
Danny Beckett's user avatar
11 votes
5 answers
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Does oxidized copper conduct electricity?

When the surface of copper turns that greenish oxidized color, does the resistance to current flow increase or isn't affected? For instance if the point of contact is secure and clean but bare ...
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4 answers
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Why is LED lighting up despite Supply voltage < Forward voltage

I have an LED which has specified Typical forward voltage of 3.5V and Maximum forward voltage 3.9V. I applied 3.3V across it with a 300 Ohm resistor in series. Why did it light up? I am wondering if ...
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10 votes
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current limiting a shorted load to 20A

Analog newbie here and first time on this forum... thank you for reading! What I have is a control for pyrotechnics. I have all the digital control stuff figured out, but analog bits are not my forte....
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10 votes
6 answers
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Prevent overcurrent while filter capacitor is charged

I have this circuit: On start-up, the power supply experiences an overcurrent condition, because when the capacitor is charged, it looks like a short circuit as seen from the power supply. How can I ...
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9 votes
6 answers
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Simplest, cheapest, fast and minimum footprint current limiting circuit with low resistance in normal state

I have a digital output, driven by the high-side driver with nominal voltage of 24V DC. The load current normally is below 100 mA. The output is monitored, so I can switch it off quickly if I detect a ...
syoma's user avatar
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3 answers
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Which reverse polarity protection is better and why?

You can find two such circuits using a diode that protects against reverse polarity, i.e. against wrong power connection. I wonder what is the point of using the D2 diode, since the current flowing ...
Jerzy Przezdziecki's user avatar
9 votes
2 answers
3k views

What is high side current limiting?

What is high side current limiting? While google searching for the term I have found ICs that describe their application as "high side load switching". Is this the same thing or something utterly ...
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Smartest way to use current limit using LM317?

As i understand, using this circuit: Will cause the current to go right through the POT and resistor, which will generate a lot of heat. Is there a better way to use current limiting with LM317 ...
Xane's user avatar
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6 answers
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Multiplexing UART

I'd like to interface my main microcontroller's hardware serial port to more than one device at the same time. My understanding is that UART on my microcontrollers is based on an active-low 5V TTL. (...
David Refoua's user avatar
9 votes
5 answers
72k views

Limiting current WITHOUT dropping voltage

I'm trying to limit a current of a 5V power supply to 100uA. I first thought of putting in a 50k resistor. That will never allow above the threshold. Unfortunately, the load requires at least 4.5V ...
TheMeaningfulEngineer's user avatar
8 votes
1 answer
1k views

Component requires specific voltage and current but the math doesn't add up

I'm trying to get an old soviet era cathode ray tube working. On the data sheet it says the heating element needs between 5.7V and 6.9V, and between 0.54A and 0.66A, but I've measured the resistance ...
Lethe563's user avatar
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3 answers
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TPS24701 Overcurrent Protection Blowing the MOSFET

I'm trying to create a circuit that will cut out if >5A is drawn downstream, using the TPS24701 hot-swap controller. It looks designed for exactly this sort of thing. Here's my cicrcuit: I clearly ...
jdf_mf's user avatar
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2 answers
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How to do a simple overcurrent protection/circuit breaker circuit for 12V 1-2A?

We're developing an I/O shield for Arduino (sort of) and having four FET controlled output connectors with approximated 12V 1-2A load each. I need all these four outputs to be short-circuit protected ...
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Help needed optimising simple current limiting circuit

I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I have started using a circuit like the one found on this ...
learnvst's user avatar
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8 votes
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570 views

How Do I Limit My Motor Current While Maintaining Voltage Drop Across It?

I am trying to build my knowledge of working with dc motors by using an IRF510 MOSFET to switch a motor on and off. Please refer to the schematic below to see how I hooked everything up. \$S_1\$ = ...
Muhammad Wada's user avatar
7 votes
4 answers
993 views

What are the drawbacks of using a voltage regulator as a constant current source?

There are similar questions asked, but none address this question so specifically. It is, quite simply the title: What are the drawbacks/disadvantages of using a voltage regulator as a constant ...
Aaron Butkovich's user avatar
7 votes
2 answers
6k views

How does this power supply circuit work?

This is the circuit of a power supply with adjustable output voltage and current, and I wish to understand how it works: What I did understand: R1 T1 VD5 - they form a voltage divider which provides ...
Denis Denisovici's user avatar
7 votes
2 answers
693 views

Current limiting resistors

I notice that in Ben Eater's project for the 74 series logic chip computer, which my son and I are building, sometimes he uses current limiting resistors on LEDs on the pins of some chips, and on ...
Kevin Hill's user avatar
7 votes
2 answers
3k views

Limiting Output Voltage of the Opamp-to avoid saturation

Problem: my photo diode recieves pulses of width 10ns-150ns and repeating at rate of 1Hz-50KHz the current from photo diode depending on incident light can go from 10nA-100mA, in a nutshell, my ...
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6 votes
4 answers
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Light bulb as limit, to what is current limited to?

I was wondering, if I use a light bulb as a current limiter when working with some electronic device, in case of a short circuit - what determines the current that is allowed to pass to the electronic ...
komrad2236's user avatar
6 votes
5 answers
6k views

What polyfuses protect USB ports in a typical modern PC?

I would like to know what is the typical rating of a polyfuse used on modern PCs (desktop or laptop) with USB 2.0 and 3.0. TE Connectivity apparently recommended in 2011 that a single USB 2.0 port (...
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3 answers
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Which side should I put the resistor?

I'm a beginner and trying to understand some basics of electricity. One thing I'm having a hard time understanding is the correct side where I should put a resistor. For example, in the following ...
André Wagner's user avatar
6 votes
2 answers
2k views

Does skin effect appear in home wires?

A technician said: Its better to use a solid cables for homes (not stranded cables). I did not use any calculations but I think that stranded cables are better due to skin effect. We use 220V / 50Hz. ...
Michael George's user avatar
6 votes
4 answers
9k views

Can electronics be damaged by under-currenting it?

Someone just asked Can electronics be damaged by undervolting it?, so now I am going to ask under-current. Let's say something requires 10A, 12V, if I limit the current to 5A, could anything go wrong?
skyler's user avatar
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6 votes
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Using a depletion mode mosfet as a current limiting device

I have recently discovered the exciting world of depletion mode mosfets. Curiously, even in this document, I found nowhere that a depletion mode mosfet could be used as a current limiting/inrush ...
MikeTeX's user avatar
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6 votes
2 answers
4k views

How to limit current precisely?

I would like a way to limit the current of a circuit to exactly 100mA (+/- 2-5%). This is on a relatively high voltage circuit (100V to ground), and the current is normally pulsed with pretty fast ...
Alex I's user avatar
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6 votes
1 answer
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Single Transistor Voltage and Current Regulator

I am in the process of designing a lab power supply for myself as a learning opportunity. However, I have hit a road block in my design. I am trying to use a single Vishay IRF520 mosfet as a DIY ...
Calyo Delphi's user avatar
6 votes
1 answer
3k views

LED strip hot / drawing more current than expected

I am trying to wire some LED strips but they are getting a lot hotter than expected. I have noticed that they are also drawing much more current than expected. I am going to show what I've measure ...
ORBstacle's user avatar
5 votes
3 answers
815 views

Add current limiter to this circuit

I made and built the following circuit. It measures current of an AC square wave of roughly ~19 V. The uController calculates a running average of 5 samples every millisecond. If the average exceeds ...
bask185's user avatar
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5 votes
3 answers
2k views

Do I need a current limiting resistor when powering an LED below its forward voltage?

I've reviewed the questions: Why can you use an LED below voltage? Is a current-limiting resistor required for LEDs if the forward voltage and supply voltage are equal? But combining them begs ...
JYelton's user avatar
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5 votes
4 answers
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How can I calculate knee current for this foldback current limiter

So as the title says, I'm trying to calculate the knee current for this schematic. I know Veb(Q2)/R1 is approximately the maximum current through the emitter of Q1 if R4 wasn't there and this was a ...
BertVano's user avatar
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2 answers
834 views

Powering Multiple Raspberry Pi circuits via GPIO header power pins

Goal: I wish to power 3 Raspi. I am currently running 3 USB C wires powering the device, but I wish to build or find ways to power them all using GPIO header power pins. Background: Mechanical ...
Hoon's user avatar
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5 votes
3 answers
111 views

Programmable current-limit on mains

Using an incandescent light bulb in series with a mains-powered device is a well known trick to limit the current used by the device. It's great for testing devices you're unsure of. Unfortunately, ...
Celelibi's user avatar
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5 votes
1 answer
215 views

Raspberry Pi Zero HDMI socket - available current?

I have an ongoing question on the Raspberry Pi SE site, in which I'm attempting to figure out how much current is available to devices connected to the HDMI socket of each Pi model. I think I've ...
goobering's user avatar
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1 answer
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Current limiters using transistors and diodes

I have been experimenting with simulating current limiting circuits. I am trying to limit current to ~500mA given a fixed 4.8V source. I started a question based on a conventional 2-transistor current ...
learnvst's user avatar
  • 1,281
5 votes
2 answers
1k views

Current limiting with optocoupler

Update: I've removed all irrelevant information and simplified the question. The OPA548 operational amplifier provides adjustable current limit that can be controlled digitally with a current-out DAC....
Maple's user avatar
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5 votes
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How is the current limited through the LEDs in this LED matrix design?

I was studying some LED matrix designs on the Net and came across the one below: DMD: Dot Matrix Display 32x16 (link to product) (somewhat poorly drawn) schematics of an old version of the product. ...
Ricardo's user avatar
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5 votes
5 answers
864 views

Dynamically dimming individual LEDs in a lighting system [duplicate]

I'm planning to build an aquarium lightning system with individually controllable LED's, I don't have much experience with electronics except from the irregular tinkering, but I'm a programmer and I ...
Alex's user avatar
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5 votes
1 answer
6k views

BJT Current limiter for linear power supply

I am trying to design a current limiter or my LM317 based power supply using this schema. The power supply must be able to provide a maximum of 1.5A@30V. I made some calculations and I would like to ...
Enrico's user avatar
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5 votes
2 answers
646 views

How to limit the current in a circuit in a DC-DC voltage buck converter

This is something I've been stuck on for quite awhile, so I wonder if I'm overlooking something. This is what I have: I have built a simple DC-DC buck converter that should be operated with an Arduino ...
Petrus1904's user avatar
5 votes
1 answer
2k views

Current measurement in a Buck Converter

We have developed a prototype of a PID-regulated Buck converter made around the AVR XMega. 6-17V at the input, 5-10 on the output, 15A current limit, 500kHz PWM switching. The issue is, how to make ...
Dzarda's user avatar
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4 votes
5 answers
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How to limit current to LEDs

I have understood that this is a bad way to do it: Since some LED can draw more current than others. So lets say I would power some high powered LEDs, like say 10 x 3W LED with a DC forward voltage ...
BufferOverflow's user avatar
4 votes
6 answers
900 views

How can I make a constant current source for a CW laser diode?

I need to power a single CW laser diode with a constant current source. I have attached the datasheet of the laser. It is a 2.2-2.4V laser whicht operates at 80mA at full brightness. I see a lot of ...
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