Questions tagged [current]

Flow of electric charge - typically movement of charge carriers, such as electrons. Measured in amperes (A).

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4answers
5k views

Limiting current from a 5v power supply [duplicate]

Possible Duplicate: Choosing power supply, how to get the voltage and current ratings? I have a 5V / 1A regulated supply. I'm thinking of using it to power a PCB which asks for 5V and 0.25A. In ...
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1answer
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Should I calculate a resistor value for driving indicator LEDs from TTL outputs?

Traditionally I have always used a \$1\:\mathrm{k\Omega}\$ resistor as a current limiting resistor for driving an LED direct from a TTL (or 5V CMOS) output. I can't remember how I came by this value -...
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2answers
240 views

A4983 driver not producing output, except when output is shorted to GND

I'm having a bit of an issue with a circuit I've built, and I'm hoping someone could provide some input. I'm making a stepper driver based on the A4983, and am having an odd issue - made even more ...
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620 views

Current sharing controller

We want to implement current sharing from two supplies on our PCB. There are dedicated ICs to implement this functionality, but we could only find UCC39002 from TI. How come no other manufacturer ...
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3answers
472 views

Simple voltage drop question

I am working on an antenna and ATMEGA-based reader. It is powered off of 2 6v deep-cycle marine batteries, and the reader/antenna draws 1 amp at 6 volts. I'm not sure about the amp-hours in the ...
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1answer
1k views

Arduino + Ardumoto : External power source

I have an Arduino and an ArduMoto. I want to use that to power 8V motors with a 17V battery (using PWM). It says for the Ardumoto that the VIN used to power the motors is the VIN of the Arduino (...
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3answers
672 views

Does direction of current flow affect induced current?

I am working on a pcb design. On the board there are two separate areas where I have a constant 5VDC trace running close to and parallel to another trace which has a pulse-width modulated 5V signal ...
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3answers
760 views

Emulating an electret microphone with a DAC circuit

Good day, I'm currently getting into DIY electronics and Netduino programming and there's this one personal project that I want to do but I'm hesitant because of lack of information. Basically this ...
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6answers
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Trying to understand the relationship between voltage, current, and power

Please forgive this ultra-noob question, but I'm a bit confused. I've been reading about how neither voltage nor current alone constitute power in a DC circuit. Instead, power is a combination of both ...
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3answers
994 views

How can I design my FPGA power supply if I don't know how it will be used exactly?

I'm designing a little dev board for FPGA experimentation using the Cyclone IV EP4CE10 but I am having a bit of trouble estimating the power requirements. I understand this depends almost completely ...
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2answers
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Circuit for testing LiPo batteries?

I have some lipo batteries I'd like to test. Ideally it would do the following: how much time does it take to discharge to minimum allowed voltage? how flat is the discharge curve? how many mAh were ...
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1answer
325 views

Can an mbed device be damaged by something drawing too much current?

The mbed has a pin which supplies 3.3V regulated current. I think it can supply up to 100mA. If this pin is used to power a device, and the device tries to draw 150mA, then what can happen? Is the ...
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2answers
619 views

How much current does this device draw?

I am using a GPS device. I'm told it's a WD-G-ZX4120, but on the actual device it says it's an ET-318. I heard from somewhere that this device uses 100 to 150mA. However the datasheets seem to say ...
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1answer
6k views

Current limiting at mains voltage

I am driving a BTB16-600BW triac using a MOC3052 exactly as suggested in the MOC3052 datasheet: The current into the power triac gate is limited using the highlighted resistor. My triac requires at ...
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9answers
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Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons ...
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4answers
1k views

Current Indicator

I want to turn an LED indicator on when current is flowing through a path. If there's no current the LED will be off, and when there's current, the LED would turn on. I've been experimenting with ...
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4answers
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different current readings with a multimeter between the 200 mA and the 10 A slots

I have a cheap multimeter, which gives me different readings between the two inputs. I would like to set 100 mA using a potentiometer in a circuit, which runs from two AA batteries. If I measure the ...
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1answer
264 views

LED current while off

I have a vague recollection that while off, a LED can actually receive light and generate a small current (in uA). Is that correct? How does that work? What is the best way to prevent this?
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how to drive 5x5 IR LEDs with 100 mA, using Arduino

I am trying to do my first Arduino project, and I would like to drive a 5x5 matrix of IR leds. I would only like to have one switched on at a time. I understand that in an array I can do it with 5 ...
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6answers
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what size of copper wire can act as a 150A fuse?

If I would like to use a piece of copper wire as a 150A fuse, what size of wire should I use? It doesn't have to be 150A very accurately, the parameters I need the wire to meet are: it needs to ...
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2answers
5k views

will a circuit breaker designed for 230VAC work for 12VDC?

Will a standard home automatic circuit breaker, designed and sold as to work on 230V AC (alternating current), and for example 16A, or 25A etc, will it work (break the circuit if it exceeds the rated ...
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7answers
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Which everyday components involve flows of charge that are not electrons?

I like this explanation of why there's nothing wrong with conventional current being the opposite direction from electron current. It mentions batteries and fluorescent bulbs as two cases where the ...
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Reading and understanding electrical specs on laptop AC adapters

My Dell laptop comes with an AC adapter with the following specs: 65 W Input AC: 100 - 240 V, ~1.5 A, 50 - 60 Hz Output DC: 19.5 V, 3.34 A My HP laptop: ...
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1answer
812 views

Can I burn out my multimeter's µA range by using a few mA of current?

My multimeter only has one 400mA fuse protecting the µA and mA range (and a 10A fuse protecting the amp range.) Is it possible to damage the microamp range by feeding milliamps through it?
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1answer
387 views

Leakage current for an SD card host

I'm using a PIC24F to interface with an SD card in SPI mode. When the card is idle, the device still draws ~200 uA of current which is unacceptable for this device's purpose. To correct this, I am ...
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4answers
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How many resistors do I need for an 8 switch DIP switch block?

I was thinking of giving each switch it's own pull-up resistor, but this seems like it would be expensive and a little bit of overkill. But using just one pull-up for the entire block seems like it ...
3
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1answer
226 views

PC Power supply for a PC/104. Current output

I have to do some work on a PC/104 CPU board. Until now I have been powering this from a separate power module (acs-5151 at the same link) that took in 8-40V and gave +12, +5, and +3.3 out. Until now, ...
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4answers
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Sizing a trace on a PCB to carry 2.5 amps

I need a trace on my PCB to carry up to 2.5 amps (average) current, with 5-6 amp spikes (it's going to a switch mode power supply.) How wide should the traces be? I've got a trade off between ...
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3answers
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Calculate Current out of Function Generator

I couldn't find an equation for this on Google/Wikipedia, but does the frequency of a function generator (we'll say that it's a sine wave) impact the current output. Example, if I had a 5 volt source ...
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5answers
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Constant-Current for a 20W LED

Can someone explain "constant-current" circuits? When are they necessary? What happens without one? What's the simplest version of such a circuit? I bought some 20W LEDs off ebay intending to make a ...
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1answer
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How does a power surge reset a modem?

Yesterday, there was a huge power surge in my area, and I wasn't able to connect to the internet any more. The reason was that the Wifi modem was somehow automatically reset to its factory ...
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2answers
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Sensor supply current?

I'm reading a datasheet for an accelerometer (specifically this) and it lists the max supply current as 290 uA. Does this mean that the power supply I use should never output more than 290 uA? Or does ...
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3answers
415 views

Voltage and current in this schematic

I'd like to understand this simple schematic to see if I get things clearly If I understand things correctly: when the switch is open, the current at the right black point is zero, the voltage is ...
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1answer
226 views

Only getting 33mA from a USB port

I attached split the end of a USB wire and attached a switch. When I press the switch, I measure 5V from the port, but am only measuring 33mA. Why am I getting only 33mA instead of 100mA?
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2answers
921 views

Hot ENC28J60 @ 132 mW

I have a problem with a relatively simple board which consists of an ENC28J60 Ethernet controller and an ATmega168. The circuit around the ENC28J60 is straight out of the datasheet and I have the ...
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10answers
147k views

How to get more than 100mA from a USB port

I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?
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3answers
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Total current consumed from a battery

I would like to know how could I know the current consumed from a battery using this sensor, or other similar, using a microcontroller. What I would like to know is shown in this video, where you can ...
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4answers
3k views

Why does Oscilloscope cause short?

I want to measure how much power my PIC is using. At the output of my 3.3V regulator I put a 1 ohm resistor in series with the rest of the circuit. I was going to measure the voltage drop across that ...
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2answers
6k views

How much current can a microcontroller/DSP pin sink/source?

I'm using a TMS320F2812 and want to drive LEDs of some of the pins. I couldn't figure out what the safe levels of current were which could go in or come out of the IO pins from the datasheet. What is ...
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8answers
43k views

Current flow in batteries?

I am reading a basic electronics book: "There are no Electrons: Electronics for Earthlings" and I came across a clever passage about the fact that you need a closed circuit in order for current to ...
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5answers
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In theory, is it possible to make a logic gate that uses zero current?

CMOS greatly reduces the current draw of ICs because one of the complementary FETs is always in the non-conducting mode, so there is only a flow of current during the transition between states, which ...
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3answers
371 views

How to supply power from vehicle to a low power device?

I am a programmer with only basic understanding of electronics/electricity. I am trying to install this device into my vehicle. The device accepts a wide DC power input (10V to 30V), but has a ...
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4answers
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Is it OK to attach an LED directly to a 5V Attiny?

From the datasheet, I though the AT90S1200 had current-limited pins and when running at 5V would sink the proper amount of current through a green LED attached to + (0 turns on the LED, 1 turns it off)...
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4answers
6k views

Arduino PWM controlling high-power LED

I'm wanting to use one of the Arduino's PWM output to control a high-powered LED. I can't remember the exact specifications, but it was considerably more current than the ATMega328 can provide. I ...
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3answers
2k views

Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...
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2answers
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Programmable current source

I need to build a programmable current source from a 8051 microcontroller. It needs an output current from 0 to 10mA maximun. How do i go about doing this? what circuits do i need to build? I was ...
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2answers
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How to redesign a circuit to use a current sinking IC rather than a current sourcing IC

I'm building a serial servo controller to learn about electronics and assembly language as part of my hexapod robot project. Quite early on I decided that I needed more I/O channels than my ATTiny2313 ...
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current sourcing, current sinking

I'm a student studying electronics and I'm having trouble understanding the concept behind current sourcing and current sinking. We've covered it in a lab using a 7404 and an LED and all that. Just ...