Questions tagged [power-supply]

An electronic device that supplies electrical energy to a load. It can be AC or DC input. Typically DC output.

The term "power supply" is extremely broad, and covers a large variety of devices.

Some examples of common power supplies:

  • AC adapters, which convert AC from the mains to low-power DC loads (commonly referred to as 'wall-warts')
  • ATX PC power supplies, which convert AC from the mains to several regulated DC outputs to power computers and their peripherals
  • battery chargers, which vary the output voltage and current to charge batteries safely
  • inverters, which convert DC into mains-equivalent AC to power devices usually connected to the mains
  • DC-DC converters, which convert DC into higher (or lower) voltage DC
  • Linear regulators, which regulate DC into lower voltage DC without conversion
  • batteries, portable but limited amount of energy

Commonly used definitions:

  • load: a circuit that draws electrical power from a power supply (a computer, a light bulb, etc.)
  • mains: (generally) AC power provided by an electrical utility
  • rectification: conversion of AC to DC
  • converter: a circuit that changes voltage from one form to another (AC to DC) or converts DC to DC using a switching stage (DC -> AC -> DC)
  • PFC: power factor correction, which generally refers to a circuit that converts the mains AC into DC while keeping the input current sinusoidal and in-phase with the voltage (making the power supply load appear resistive to the mains)

Wikipedia power supply article

You are ok if your power supply can have the same voltage and the same or more current. The reference question for choosing a power supply is Choosing power supply, how to get the voltage and current ratings?

Common Switching-mode Power Supply(SMPS) Types:

  • Buck: A SMPS that will take in a higher voltage and step it down to a lower voltage. An inductor on the output rail of the power supply is characteristic of this topology.
  • Boost: A SMPS that will take in a lower voltage and step it up to a higher voltage. Generally, an Inductor in the input rail to the power supply is indicative of this topology.
  • Buck-Boost: A hybrid SMPS that is capable of both the buck and the boost topology. Generally, this will have an inductor on both the input rail and the output rail of the power supply in which only one of them is internally engaged at one point.
9102 questions
322
votes
6 answers

Choosing power supply, how to get the voltage and current ratings?

Power supplies are available in a wide range of voltage and current ratings. If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify? What if I don't know the device's specs, but…
Olin Lathrop
  • 310,974
  • 36
  • 428
  • 915
110
votes
6 answers

My linear voltage regulator is overheating very fast

I'm using a 5 V / 2 A voltage regulator (L78S05) without a heatsink. I'm testing the circuit with a microcontroller (PIC18FXXXX), a few LEDs and a 1 mA piezzo buzzer. The input voltage is aprox. 24 VDC. After running for a minute, the voltage…
m.Alin
  • 10,638
  • 19
  • 62
  • 89
91
votes
12 answers

How can I tell the size of a barrel power connector?

Spring cleaning, and I'm trying to get power supplies for all my devices with missing power supplies. They're all the typical barrel power connector, and I'm having a dickens of a time trying to figure out the pin/hole diameter. I ordered the…
dwwilson66
  • 3,402
  • 11
  • 33
  • 42
74
votes
3 answers

What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices?

I have found that many USB wall chargers use a resistive voltage divider to set the D+ and D- pins to a specific voltage, usually between 2 and 3 volts. Other USB wall chargers short the D+ and D- pins together with no connection to anything else. …
72
votes
6 answers

Why do many laptops run on 19 volts?

Typically mobile devices that have a mains-powered supply will accept voltage that is multiple of some single battery voltage. For example, 4.5 volts is 1.5 volts (AA primary battery) 3 times and 36 volts is 3.6 volts (Li-Ion battery) 10 times. Now…
sharptooth
  • 12,374
  • 26
  • 83
  • 144
67
votes
8 answers

Why do we need an isolation transformer to connect an oscilloscope?

My professor always insists that I provide power to an oscilloscope thorough an isolation transformer. What is the necessity of this? What is the risk if I don't connect it?
noufal
  • 1,575
  • 3
  • 20
  • 25
66
votes
4 answers

What's the purpose of two capacitors in parallel?

What's the purpose of the two capacitors in parallel on each side of the regulator in this power supply circuit I've seen similar setups in other similar circuits and can guess that it's related to one being polarized an one not, but I don't really…
Brad Robinson
  • 1,185
  • 1
  • 9
  • 22
66
votes
7 answers

Why is my circuit so incredibly sensitive to electric fluctuation?

I recently finished building a circuit showcased in a beginner’s electronics book. I have included the picture of my creation below because I think it may become relevant to the question. At the beginning of the build process, the instructions…
T555
  • 1,569
  • 2
  • 17
  • 27
65
votes
4 answers

Can I replace all electrolytic capacitors with ceramic?

I am designing the power supply circuit for a system that needs several supplies, my questions are: Is it possible to replace all electrolytic caps (Mostly 100uF) by ceramic ones? What are the limitations of ceramic? Should I use a 2x voltage…
Abdella
  • 2,605
  • 4
  • 30
  • 38
57
votes
1 answer

What does this symbol mean on my Samsung travel adapter?

The charger was bought in Austria two years ago, and I know about all symbols/labels except this one. Google reverse image search did not help.
54
votes
13 answers

What kind of components in a computer power supply can explode loudly?

Today I heard a loud bang that tripped the circuit breaker in my server room. It must have been really loud because I could hear it 2 rooms away through 2 heavy doors and it was like a firecracker going off right next to me. Long story short, it…
user81993
  • 831
  • 1
  • 9
  • 14
51
votes
3 answers

What's the reason to make power supplies external?

Many years ago most electronic devices had internal power supplies only - there was a mains voltage cable running into the unit where mains AC would be converted and distributed for consumption. That was typical for shavers, TV sets, monitors,…
sharptooth
  • 12,374
  • 26
  • 83
  • 144
50
votes
3 answers

When a battery is your power source, what is ground?

For the sake of not incorrectly connecting my power supply and damaging my board I'm going to ask a relatively dumb question. Is ground on my board the negative terminal on my battery? Explicitly should I connect the ground to the negative terminal…
QueueHammer
  • 719
  • 1
  • 6
  • 9
49
votes
4 answers

Why do fire and security systems run at 27.6 V?

I have been looking at buying power supply units for a project, and I keep seeing supplies that output 27.6 V. It's an unusually specific number, so what they are used for, and why is it important that they produce 27.6 V? It appears that these are…
Lucas
  • 609
  • 5
  • 5
47
votes
4 answers

Why don't we use wireless electricity today?

I was reading about Nikola Tesla today (via the Oatmeal) and read about the Wardenclyffe Tower which (among other things) was intended to transmit electricity wirelessly. Forgive the naivety of the question, but if technology that could transmit…
n00b
  • 581
  • 1
  • 5
  • 8
1
2 3
99 100