Questions tagged [power-supply]

An electronic device which supplies electrical energy to a load. Can be AC or DC input. Typically DC output.

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2answers
1k views

Source switch between two batteries

I've found several answers on switching between an Adapter and a Battery. But I need to autmoatically switch between two batteries. One of them is 'hotplugable'. Problem: I've got a Solarcell which ...
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1answer
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Transformerless power Supply - 24VDC, 120V AC and 230V AC

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals. Thus, the output should be xxV DC (5-24 or whatever is decided ...
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LED Strip Light - Power supply issues

I'm making this right now - https://www.youtube.com/watch?v=qlMtakaa7u8 Each 5m roll of LED takes 60W power (http://www.ebay.com/itm/182028302443?rmvSB=true). He's using two of these rolls, so a ...
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Synchronising Power & Synchronising Coefficient

I am really confused with the concept of synchronising power and synchronising coefficient. I was taught 2 simple formulae in class. P = 3VEsin(del)/X Sp = dP/d(del) = 3VEcos(del)/X Now, I am ...
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Transmission Line Inductance

I went for an interview in BARC India for scientist position. They asked me to draw short transmission line. Then they started asking What does inductance represent? I said leakage while ...
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1answer
862 views

Designing 12v DC UPS

My requirements are: I need a UPS system which supplies power to a 9 volt modem. UPS should Charge 12v battery (SLA , charging curent 800ma), and it should have overcharge/discharge protection system [...
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What amp rating of 24vac transformer for LM317T

I am trying to post a new question about the lm317 to-220. I just want to know what size transformer for lm317 at full 30vdc. I know its a 24vac center tapped transformer but is it 1 amp or 5 amp ...
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Why graphical representation of a DC current/voltage is a straight line? [closed]

Why does graphical representation of a DC source always a straight line?
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Why do buck (step-down) switching regulators require an inductor and diode?

So, I understand, at least at a basic level, the method of operation of switching converters, both buck and boost. What puzzles me, though, is why buck converters in particular aren't simpler. Why ...
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Can the noise of any switching PSU be attenuated if I put linear regulator before the output?

A friend told me that noise of any switching PSU can be attenuated if I put linear regulator before output. Is that true? For example, if I want to power a +-12 V op-amp for an amplifier, I can ...
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Ferrite bead position

I wish to use some extra power supply filtering for my DAC, ADC, CPLD and OpAmp devices. In this question I got the point about the global locations for ferrite beads. If I understood correctly, the ...
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1answer
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How much current can you pull safely off a standard AAA battery?

This might be a stupid question. But how much current can you safely draw from a AAA battery. I am currently powering my project from a worktop power supply and it draws at 5V 0.45A during normal ...
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24VAC/5VDC power supply design

I am planning to create a water valve controller using an MCU and a set of solenoid-controlled valves. The solenoids run on 24VAC (40mA inrush, 20mA holding). The MCU is on a board that draws ~100mA, ...
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What is a good power electronics textbook? [closed]

I really want to learn as much as I can about power electronics, switching mode power supplies, and overall analog design. Unfortunately my universities computer engineering program is still ...
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6answers
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Benchtop power supplies: linear vs switching? [closed]

I'm looking into getting a decent benchtop power supply ($150-300) for hobby-level electronic design and testing. I don't want to modify or use a computer ATX supply because I want: Adjustable ...
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4answers
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12V DC UPS for Network Equipment

My requirement is to keep running supply of low power devices like DSL modems, etc. Most of these devices input 12V/9V DC so i don't see the value in using ordinary UPS which converts DC to AC then ...
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How to find the ESR of a capacitor

I am building a power supply circuit, and the switching regulator (L4963) calls for a low-ESR output capacitor. The capacitor in question is C3 of the evaluation board circuit. What does "low" mean? ...
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Circuit to safely power-down Raspberry Pi

I want to use a Raspberry Pi as an XBMC server in the car. The XBMC docs say that you should always use the shutdown command before disconnecting the power. I don't want to have to (tell my wife to) ...
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Making LM317 output voltage adjustable down to 0 V

I want to design a variable voltage regulator that will get from it`s maximum output (lets say 10V) down to 0V (or very close) considering the input as regulated 12V (from a PC power supply). All the ...
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Voltage regulator vs. voltage reference

I need a cheap, somewhat accurate (~0.5%) voltage reference for some DACs. At first I was going to use a LDO voltage regulator (a TC1223 specifically) for this, it seems to fit the bill looking at the ...
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How can I tell (easily) if my power supply is regulated/switched or unregulated/nonregulated?

I found this great blog post about unregulated vs. regulated and switched power supplies. I've got a specialized need for a Regulated 12v power supply and a handful of wall-warts and bricks laying ...
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24V 3A from ATX power supply?

I am looking for a cheap way to get +24V DC max 3A from computer power supply. I prefer easy soldering solution like DIP, and standard components that do not need to be purchased over internet. Any ...
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Power Supply Design - Multiple Voltage Regulators

I'm trying design a benchtop DC power supply for powering small projects, breadboards, arduino, etc. This is a list of what I want from it: Fixed voltage rails for 24V, 12V, 9V, 5V & 3.3V Edit: ...
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1answer
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Noise problem with buck/boost switching regulator

I am designing a electrical device for a research project (I'm a PhD student, but unfortunately not EE!). More info on the device can be found at http://iridia.ulb.ac.be/supp/IridiaSupp2012-002/ The ...
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How to dimension a power supply transformer?

I always hesitate when dimensioning a transformer for a DC power supply, and I guess I sometimes overdimension them. My confusion stems from the difference in transformer and DC voltage. If I need 10V ...
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Automotive power filtering, protection - feedback needed

I'm working on GPS tracker for automotive applications. Device should work in 9V-30V supply voltage range. In practice it will be fed from 12V car installation. This enforces the implementation of ...
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5answers
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Ultra low noise power supply

I am trying to design an ultra low noise power supply for my sensitive circuit. The supply will provide 5V and 600mA. (Worst case, 200mA typical). My input voltage is 2V to 4V. My ripple target under ...
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3answers
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Simplest possible 5V to +/- 10-15V converter (for op-amps)

Im looking for simplest possible solution to power op-amps from USB or phone charger. Requirements: +5V input voltage ±10V to ±15V output voltage at least 10mA output current on both rails (+/-) ...
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2answers
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Op Amp's Negative Power Supply to Ground

I am using a standard 741 Op Amp from TI. For me to amplify any signal, I am required to set +Vs = 15 Volts and -Vs = -15 Volts. I am now concerned as to what will happen if I connect -Vs to 0 (...
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Is this negative regulator really meant to be an inverted positive regulator?

Project: make a power supply that can replace the 240V AC supply shown, so that I don't die when messing with the board that this connects to. I'm only interested in the part inside the yellow box; ...
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Converting passive USB Hub to powered USB Hub, by adding regulated wall-wart as power supply?

From a quick price-check on ebay, Passive (bus-powered) USB Hubs - ~ $2-$5 Powered (externally) USB Hubs - ~ $15-$20 My use-case is to expand the no. of USB ports on a ARM-based SBC, and to embed ...
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Is current flowing backwards a bad thing?

In the circuit below: I find it awkward that the direction of the current on the 2V power supply is running opposite to the direction of the current on the 5V power supply. In the 5V power supply the ...
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1answer
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Simulating an automotive load dump with a bank of charged capacitors?

I've been working on a data logging device that will eventually go into my personal vehicle. I've scoured the interwebs and built what, in theory, should be a fairly stout power supply capable to ...
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How do I design a device to automatically switch to the backup battery?

I've been told that many kinds of batteries work best if they are used until they are completely drained, and then recharged. (Edit: The "memory effect myth" is quite widespread. Batteries work just ...
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4answers
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Different ways to digitally control an adjustable SMPS

I want to make a battery powered, adjustable SMPS for use in situations when I cannot have an outlet near me, so I would like some more information or suggestions about this topic. The SMPS chip I am ...
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What is the COM terminal on a DC Power Supply?

We have a HP E3631A power supply at my university's lab. There are 6 ports. My questions are as follows. What is the green port titled 240VDC Max? I was explained to an extent that it was the ground ...
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Calculating Power Loss in Switching Power Regulator?

I am new to the construction of DC/DC power supplies (still a university student) and have built basic supplies using simple linear voltage regulators. I have recently discovered the world of ...
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4answers
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LM317-based adj power supply output takes a while to stablize

I recently built-up a quick little LM317-based adjustable power supply schematic: However I've noticed the output can take several seconds (on the order of 10 or so) to "settle down" after turning ...
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Selecting input voltage for 7805

I generally use switching 12V power supplies for my circuits since they are so common, but I understand the 7805 can take a lower input voltage. If I gave the 7805 a lower input voltage (i.e. 9V), I ...
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2answers
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Inductor selection for obtaining a noiseless analog power rail

I interface an image sensor, and the design schematic for power supply is: How do I choose one from the available 3uH inductors based on the specs? I figured the maximum current and dc resistance ...
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Why do we need 3 phase power supply?

Why do we need 3 phase? For the reason that voltage will never be zero in 3 phase? OR we need high voltage?
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3answers
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What is the thought process for specifying an EMI bypass cap on line transformer secondary?

Update It turns out I had mistakenly interpreted the role of the capacitor in question here as an EMI filter for line noise. It looks like a capacitor in that position actually serves as a snubber ...
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High Voltage Series Pass Transistor - Low Voltage Control

I am having some difficulties getting my output stage to work correctly. Here is some info: I have a +48VDC source with a series pass transistor to drive a load between +45V and 0V. The control ...
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1answer
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Dual polarity vs dual rail power supply

My previous post turned out to contain too many questions, so I'll focus on the main one first, and figure the rest out as needed. I'm looking at building a DC lab power supply, roughly 1.2-14 volts ...
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2answers
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Connecting switch-mode power supplies in series to increase voltage [duplicate]

I have two identical 48 V switched power supplies, both of which can deliver the same current of, say, 4 A. Can I connect them in series to get 96 V at 4 A? Is this something ...
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Which way does electricity power a circuit?

Working with some circuits this summer, I ran into what everyone eventually does: Current flows from + to - despite the electrons flowing (well, bumping into eachother) from - to +. I understand the ...
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Why are laptop power supplies marked “IT equipment only”?

Laptops are often shipped with switching power supplies that among other have a phrase for use with information equipment only on their body. Why can't I use the same power supply to power a motor or ...
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Apple power supply: thick AC cable, thin DC cable - why?

Apple power supply consists of a very thick, inflexible AC cable (wall outlet to converter) and a very thin, flexible DC cable (converter to computer): Why? The currents through the cables should be ...
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4answers
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Why would a power supply unit with insulating case and galvanic separation need a grounded power cord?

Recently I witnessed an external IBM laptor power supply that looked like a usual switched-mode power brick (rather small and lightweight for it more than 50 watts power) in plastic case but had a ...
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Routing a buck/boost DC/DC converter

I need some help with the layout of a power supply. I botched the first two iterations as I do not have the necessary experience, and I would like to avoid another costly run. For the sake of ...