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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2answers
37 views

Voltage in a circuit with variable resistance and diode in series?

I came across some examples to calculate the current in a circuit with diode and resistance in series. Consider the circuit below: Current was calculated as follows: I = (9 - 0.7)/R1 Does that mean ...
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1answer
73 views

Value of resistor to limit current to 1 ampere in 12 volts circuit

I want to connect my modem directly to a 12volt battery so that I dont need a adapter. My modem’s specs says that it need 12 volt 1 ampere as input.Now the voltage of 12 volts can be directly given by ...
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1answer
58 views

Current limiter problem

I am designing the following circuit to limit current inrush to a device on startup (to about 1.5 amps over about 3 seconds). Rload is just for testing, the actual load is a bunch caps at 56v, but I ...
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92 views

LED fairy lights with series capacitor?

I've opened up the battery box of a string of fairy lights (like pictured at bottom) and found a resistor, plus what looks like a capacitor in series with the lights. Is this really a capacitor? If so,...
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44 views

How to split high current low voltage? Voltage regulators , current regulators(?)

I am using a 20v dc laptop charger that supplies 4 amps. I need 5v dc 4 amps. When I use a linear voltage regulator it’s too much current to pass through safely.. 15 amps change and 4 amps, so I use a ...
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23 views

JFET Constant Current Source (CRD alternative)

Today I have build constant current source based on J111. To drain I connected VCC it's 24VDC from laboratory power supply, then I connected resitor 470Ohm between gate and source. To source pin i ...
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25 views

LED circiuit for a current limited circuit

I have the following requirements for a circuit: The circuit is supplied from a 500mA current limited voltage source The circuit should indicate the status of the supply, i.e. if it is in current ...
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1answer
64 views

Get the max current through relay without activating it

I have a circuit where the only current I can get to supply my battery is the one that I can get from a relay connected to Vcc. When it is not pulled to GND I can get current without activating it up ...
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1answer
30 views

Limiting the current with the LM2679

I'm building a power supply, and I'm trying to see if the LM2679 will fit my needs. I like how it's similar to the LM2596 as well as the fact that it has a pin to limit the switch current. However, I ...
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52 views

24V battery charger with LM723

I have a 28V steady DC input, and I want to use it to charge 2x12V lead-acid batteries in series. I want to use the LM723 IC to make an adjustable (26V to 28V) regulated output, as it has current ...
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1answer
44 views

What will gain be when both the zener diodes are conducting?

I have seen in solution that they have considered both 10k and 20k to be parallel when both the diodes are conducting. How will 10k and 20k be in parallel when zener diodes are conducting? Why are we ...
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1answer
40 views

Limit current through Force Sensing Resistor

I am using an ICL7660 chip to provide a negative reference supply to an inverting op-amp set up for a Force Sensing Resistor (FSR). The minimum resistance of the FSR is about 1kohm, this means that ...
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6answers
143 views

Ohm's law and the voltage drop across a resistor

I'm trying to wrap my head around Ohm's law and there are plenty of similar questions already asked in this forum. But I just still don't understand it. It's about calculating resistor values. Let's ...
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1answer
51 views

Does voltage drop limit the maximum current that can be draw?

I'm a newbie to this area. I'm having a few questions about the ohm law. The given scenario is, In the circuit, there is a power source of 5V, and a resistor of 1 ohm. This means there will be 5A ...
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1answer
59 views

Limit the wall to 15a [closed]

First the Bridge Rectifier of course... If I find a normally on transistor (PNP) rated for 120v, put it in series before the load and have the circuit circle back to the gate after the load and the ...
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1answer
127 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 ...
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1answer
45 views

Do I have to protect the CD4013 outputs from short circuits?

I'm trying to determine whether a CD4013BE ("CMOS Dual D-Type Flip Flop") can take damange if one of the outputs (Q or Q-bar) is set to high, but shortened to ground (or vice versa) with no resistor ...
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24 views

Current limiter IC for motor driver

I'm using a full bridge motor driver to control a brushed DC motor. The motor driver can provide up to 20A at 24VDC and I'm using 24VDC, 200Ah AGM batteries. The driver offers the possibility to ...
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33 views

A high power IC with adjustable current

I have a transformer that can output 5 volts and 18 or 36 volts via two separate secondary winding. I would like to create a high power voltage circuit that allows me to control the output current. ...
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2answers
38 views

Can a transformer output current be controlled by a current limiting switch on the input?

I have a step down transformer, input of 220/40v, however I need to vary the current on the output. I understand that by varying the voltage (using a device such as a Variac) on the input I could ...
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239 views

How to calculate RMS current from the rated current? Are they the same in a stepper motor?

I want to use the TMC2130 driver with the stepper motor I show below. This driver has these main features amongst others: Integrated power MOSFETs handle motor currents up to 1.2A RMS (QFN package) / ...
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1answer
67 views

Limiting current on demand [closed]

I’m reimplementing a certain proprietary USB cable. The other end of the cable among GND, VCC and data lines also features ID line I implemented that identification protocol on a FPGA, but according ...
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6answers
763 views

Short Circuit Protection of High speed Data lines

I need to protection data lines of a PIC32 micro-controller (SPI and parallel) running at ~10 MHz, from shorting to ground/Vcc or mis-wiring. I usually (in low speeds) use series resistors to limit ...
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1answer
36 views

Limiting the Current of a Constant Current LED Driver which is Driving a Halogen Bulb

I am powering a 12V, 35W halogen bulb with a MeanWell HLG-100H-20B constant current power supply. The "B" version of this power supply has a really neat dimming control system which lets one control ...
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1answer
114 views

LM317 VS AMS1117 as Constant Current Limiter for LED SMD Boards

i need to design some board like this: each led is SMD 5730 type with current max 150mA in three line and input voltage almost 3.2×7~23V, to create some SMD led board like this: so i have seen this ...
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2answers
58 views

Constant current density

I am reading an article that says ... constant current density of \$−1.0\,\mathrm{A \cdot cm^{-2}}\$ Let's say that I have material that's \$2\,\mathrm{cm^{2}}\$, how would I calculate what's the ...
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40 views

How does difference in loads affect current draw

This is a side question to 487370/limit-charging-current-to-a-smartphone. Hopefully it will clear the confusion in my head. Say we start at 5.5V with a series resistor of 1 ohm, that will leave 5V ...
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2answers
68 views

Limit charging current to a smartphone

I'm using an LM2596 buck converter set to 5.0V to power a bunch of stuff among which is a smart phone. My total consumption is around 1A excluding the phone. I'm not really sure what will happen if ...
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1answer
81 views

Limiting current without dropping volts [closed]

Can I limit 12v 25A current to 18A without dropping that 12v?
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2answers
74 views

Single Resistor on Common Cathode Display Is Not Limiting Current (With 1 segment lit)

Today I did a little test and hooked up my arduino nano to a seven segment common cathode display. I attached a single 1k resistor to the cathode pin of the display, and then lit a single segment ...
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3answers
59 views

Supplying power to a 12V motor with 5V and 2A adapter

A very elementary power supply question but i couldn’t find the answer with Google, so I would appreciate a response. I’m using a 12V, 340W DC brushed motor for a personal project. While the motor is ...
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0answers
56 views

Why does a 1.8mA current draw still create a blue glow in my Nixie Tubes?

I've created a Nixie Clock with 6 IN-14 Nixie tubes. I've run into the issue where the tubes have a faint blue glow surrounding the digits. I've heard this is due to the Nixie tubes being over-amped ...
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3answers
289 views

How is the 741 op-amp output protected when shorted to V+?

I have completed my answer to the question about the Widlar's limiting circuit but there is something unclear to me - how the transistor Q22 manages to limit the load current when the output is short-...
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2answers
39 views

Calculation of max possible current load from voltage multiplier connected to PSU 12V rail [closed]

today I found in a box a PSU with two 12V rails each delivering 17A (Fortron SAGA II 400W) and decided to step-up the voltage so can feed the DPS5020-USB DC-DC converter (rated at 60V/20A max output). ...
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2answers
310 views

What is the idea behind the ingenious Widlar current limiter?

For a long time, I had the idea of this circuit as a short circuit protection. I first saw it in the output stages of the Widlar's 301 and Fullagar's 741 op-amps... and knew it was Widlar's invention. ...
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110 views

How to active limit the current from a DC source

I have a source with variable power output during the time because it is shared with another devices and this source has not enough power to feed my load (a battery charger for a 1 cell 4.2V lipo) so ...
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2answers
70 views

Current limit resistors for Optocoupler controlled Mosfet

Reading different design rules regarding optocouplers used as switch I have a question about the current limiting resistors R4 and R6 One aspect is the protection of the devices (e.g. ~200Ohm for a ...
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1answer
28 views

BQ297xy Overcurrent protection

Can someone explaine to me how dose this overcurrent protection works and how to calculate it? BQ297xy Schematics
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2answers
56 views

Current limiter low voltage drop

I'm trying to understand the function of the constant current regulator CCR and the zener diode 1N5338. I do have more questions but these two components is probably a good start. I understand that a ...
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1answer
53 views

How to incorporate voltage controlled current limitation

This is part of a lab PSU and programmable load, for generic lab use including e.g. battery charging/discharging. This question is about the desgin of the current limiter in the psu part. It must be ...
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1answer
66 views

Transformer open circuit output voltage and current limiting resistor at gate of Triac

Im kinda new to electronics and have some questions before i solder my projekt together. I want to make an Arduino controlled soldering iron and designed the circuit below. The optocoupler i used is a ...
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1answer
109 views

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 ...
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99 views

LM317 using 2N2222 as current limit

I am trying to build a current limiting circuit using LM317. The goal is to limit output current to ~150mA with 25V input and output at >20V. I built the circuit according to ST datasheet, using the ...
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1answer
97 views

Do I have to use current limiting resistor for LED in this configuration?

LM741 datasheet says that it can output a maximum of 20-25 mA. So in this case, is that R5 a must, or will it be safe not using it? Assuming LEDs can withstand 25mA.
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3answers
276 views

Limiting output current of a Buck Converter

I am trying to power a 4S-ESC to drive a BLDC motor using a buck converter and 24V,10A SMPS. However, my buck converter can only handle 10 Amps of current (safely) at 15V through its output side. ...
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0answers
28 views

How to calculate the maximum current that a wire can handle? [duplicate]

What are the methods that manufactures used to do so ? What is the formula used if there is a one to do so?
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1answer
301 views

Implementation of Adjustable Current Limiting Circuit

I have a circuit that can deliver 0-10V and 0-100mA to a load, and want to have an adjustable current limit that will limit the current delivered. To do this I have a current shunt that I monitor, and ...
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1answer
68 views

LED current source safety margin

I have a power LED that requires 600mA at around 25 Volts. Since there are mainly 24 Volts and 36 Volts power supplies available on the market for a reasonable price, I needed to choose a 36 Volts ...
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1answer
88 views

Creating High current DC Power supply [closed]

I have the following resources: Input - 24 V 80 Ah DC Battery (Car Battery) Output, what i want: 12V DC with <2 Amp for driving some of the sensors. 5V DC with <2 Amp for driving micro ...
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0answers
63 views

Op-Amps in custom current limiter acting strangely

I'm building a small current limiter (~20 mA). It's important that there is little drop over the current limiter and that the load receives almost the full supply voltage when it's pulling less than ...

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