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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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 ...
1answer
3k views

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 ...
3answers
3k views

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 ...
1answer
2k views

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 ...
2answers
165 views

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 ...
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 [...
2answers
98 views

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 ...
3answers
2k views

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?
6answers
11k views

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 ...
6answers
25k views

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 ...
5answers
26k views

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 ...
1answer
24k views

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 ...
5answers
7k views

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, ...
3answers
6k views

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 ...
6answers
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4answers
4k views

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 ...
1answer
3k views

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 ...
3answers
9k views

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 ...
4answers
3k views

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 ...
2answers
16k views

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 ...
2answers
16k views

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 ...
4answers
5k views

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 ...
5answers
10k views

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 ...
2answers
2k views

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 ...
5answers
55k views

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?
3answers
767 views

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 ...
2answers
4k views

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 ...
1answer
6k views

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 ...
2answers
21k views

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 ...
2answers
660 views

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 ...
4answers
4k views

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 ...
8answers
6k views

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 ...
4answers
6k views

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 ...
2answers
2k views

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 ...