Questions tagged [power-supply]

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

Filter by
Sorted by
Tagged with
270
votes
5answers
356k views

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 ...
101
votes
6answers
61k views

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 ...
48
votes
6answers
26k views

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?
50
votes
3answers
59k views

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- ...
20
votes
4answers
19k views

How do I select the accompanying components for an optocoupler?

I'm using an optocoupler (MOC3021) to sense the On/Off state of an electrial appliance using a microcontroller ATmega16L. How do i go about doing this? My mains supply specs are 230V, 50Hz. How do I ...
15
votes
4answers
16k views

OR-ing power supplies (diode or mosfet)

I have got two power supply options on my board: USB 5.0V DC Power Jack of 5.0V My intention is to design a or-ing power supply option, as either of them will be used at a time. Possible solutions ...
14
votes
2answers
7k views

Is it normal for DC wall adapter power supplies to provide voltages above the nominal ones?

When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my 1117CD-5.0 ...
37
votes
5answers
15k views

Switch between 5V power supplies?

I'm designing a board that can be powered either by USB or an ATX power supply. They can both be plugged in at the same time, independently. I'd like the ATX to provide 5V if its plugged in, but ...
31
votes
3answers
14k views

How can I detect a power outage with a microcontroller?

I have the following power supply configuration: AC MAINS -> UPS -> 24V POWER SUPPLY -> 5V VOLTAGE REGULATOR -> PCB (microcontroller). What's the best solution to detect the power outage on the mains ...
19
votes
3answers
74k views

What are the ways to make a dual power supply from a single voltage source?

I have a function generator IC XR2206 from EXAR. It's application circuits uses dual power supply +/-9 volts. How can I make such a 9-0-9 dual supply from a single voltage source like a battery or an ...
56
votes
4answers
89k views

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 ...
6
votes
1answer
12k views

switch between battery and usb power no microcontroller circuit

Following an earlier question about how to switch between battery and USB power, I would love to implement the TC2014 LDO as suggested by Russell McMahon. That way I could switch between 4AA ...
9
votes
7answers
39k views

How do I design a 2A or more power supply for my consumer USB devices?

I understand that many of my consumer devices charged by USB ports can charge at higher rates than 0.5A. However, in testing, I've found they don't consume more than this. Test Setup I have a power ...
14
votes
2answers
5k views

Calculate battery life

I would like to know how to calculate battery life when using an LED strip. The LED strip is powered by 8 AA batteries in series. LED Current Draw = 260 mA. LED power consumption: 3.1 W. LED Operating ...
2
votes
1answer
579 views

How does a cell phone charger work? [closed]

I have studied that there is a transformer which steps down the ac voltage after then bridge rectifier to convert into ac to dc and then given to filter, this is what I have learnt in books, but when ...
45
votes
3answers
37k views

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 ...
12
votes
1answer
4k views

'Voltage Fuse' or better

I have a power supply with multiple outputs (5v, 12, 24v) According to the manufacture (and after testing) there must be a minimum load on the PSU for it to supply the stated voltages. Without a ...
1
vote
1answer
626 views

Draw power from a portable mobile charger to power circuits

I usually power my beginner prototype circuits using mb102 power supply board, but it needs an external elimeter to draw power and then regulate it. I was looking for a portable solution for my 5 ...
40
votes
11answers
144k views

What would happen if I connect two different DC voltage sources in parallel?

I have a computer power supply that I'm hacking together as a bench supply. For this particular model to power on, I need a minimum load across both +5V and +12V. "Easy," I thought, "I'll just ...
17
votes
7answers
7k views

Why can sticking fingers in an electric outlet kill you?

I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing ...
14
votes
4answers
22k views

Shutdown Controller for Raspberry Pi in a car

Following on from my previous question I'm trying to create a shutdown controller for my Raspberry Pi. The Raspberry Pi needs to be powered from the battery, but should power-down after the Pi ...
25
votes
6answers
31k views

How efficient is a capacitive power supply?

Something like this Falstad sim version of it (I'm tired, I keep making mistakes, so please excuse me for the second time.) Now these are not very safe PSU's, due to the lack of isolation. But in ...
6
votes
1answer
1k views

Why my DAC works without GND and VCC?

This is the most interesting thing I have seen! I have built a DDS that sends data (D0-D7) to a DAC (ADV2175). The design worked fine and I just have a low frequency alias noise (a question here). ...
12
votes
5answers
37k views

Can electronics be damaged by undervolting it?

I was wondering if there are some particularly important mechanism by which one can break electronics, when undervolting it. Its pretty obvious that lots of electronics will not work properly if ...
4
votes
2answers
1k views

Microcontroller soft off circuit not working - why?

I was making a board with an atmega328 mcu (to be used with Arduino libraries) to do some one wire communication stuff. Since I was etching the board anyway, I decided to try and implement a simple ...
57
votes
4answers
58k views

Can I replace all electrolytic capacitors with ceramic ones?

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 ...
28
votes
6answers
23k views

How to convert AC to DC

I am designing a circuit that needs to output 5VDC @ 1A. I'm trying to use a wall transformer to step the voltage down to 12VAC. The next step is the diode bridge and ripple capacitor. The ripple ...
26
votes
1answer
21k views

What to do with third contact in DC barrel plug with only two input contacts

My AC-DC adapter gives output of 12V and GND. I tried to search for suitable DC barrel plugs and found that most of them have three terminals So, pin 1 is positive in my case. 1. Which pin should I ...
4
votes
5answers
23k views

Does an ATX PSU's PS_ON Signal Require Resistance

As the title suggests; when connecting the PS_On signal directly to ground in order to switch on an ATX PSU, is there a required amount of resistance? - To try to clarify my particular problem; I ...
3
votes
2answers
4k views

Is it safe to use a voltage divider for Arduino and DC motor controller?

I have ordered a Dual H-Bridge 12A continuous (30A peak) Polulu motor driver shield for my upcoming (first time ever, a 1.2m long tank made of wood) robot project. I was thinking about how to supply ...
0
votes
2answers
2k views

Making dual power supply from single for opamp?

For the circuit of opamp 741. we have to supply the dual power for it. How can I make a dual power supply from single. For example, make a (+9V)-GND-(-9V) from single 9V battery ?
0
votes
4answers
397 views

In any electrical equipment having single ph 230 v ac supply ,if neutral and earth wire exchanged then what will be the consequence

I am handling the supply in a locomotive coach and have noticed that the neutral and earth wires have been accidentally flipped,inside the appliance(hot case) is there a problem from the safety point ...
0
votes
3answers
2k views

Input power rating on power supplies - how does max amp draw apply to 220V

If a power supply says the input power is 100-240V, ~1.5A, I'm assuming that the "1.5A" draw would be at 100V, not at 240V, right? I.e. would the total max watts be 150W regardless of the input ...
16
votes
3answers
9k views

How to implement a soft power switch controllable by microcontroller?

I want to design a circuit such that the microcontroller can toggle a GPIO pin and shut the whole system (including microcontroller itself) down. And when the user presses a momentary button, the ...
27
votes
7answers
5k views

Why is this power adapter transformerless?

I saw a battery charger that converts 220V AC to 6V DC without a transformer. Now I am wondering why many (if not all) power adapters are using a transformer, is it about efficiency or about ...
18
votes
5answers
31k views

Is full wave rectifier better than half wave one?

I am curious if there are practical differences between a DC power supply based on a half wave rectifier or a full wave rectifier. I mean I have a few small DC power supply units which should give ...
38
votes
3answers
29k views

How is wristwatch with 10 years battery life possible?

Turns out Casio offers a handful of wristwatches with "10 year battery life". The claim is that thanks to "an advanced technology" the battery life in those watches is extended to ten years. Now if ...
14
votes
7answers
9k views

How can a faulty USB charger kill you?

This question relates to this incident here, where a women in Australia died from a faulty USB charger that allowed the full 240V mains voltage through the USB cable. Now from my understanding you ...
12
votes
3answers
7k views

How to discharge smoothing capacitors?

I have a simple 12V 10 A power supply with just a transformer and a rectifier. After doing some research and simulations, I've added 3 10 mF capacitors in parallel to smooth out the output. My ...
4
votes
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 ...
2
votes
2answers
1k views

3V power rail from 5V

I've mistakenly ordered some 3V PIC18 L F14K22 instead of the 5V 18F14K22. 3V output is fine for the designed circuit but I need to make a 3V power rail from the available 5V rail. Since only a ...
2
votes
2answers
35k views

Full wave rectifier capacitance calculation

For making 100 amperes, 50 volts full wave rectifier, how do I calculate the circuit capacitance to avoid the ripple voltage? I mean which size of capacitor should I use?
1
vote
2answers
4k views

How to force variable voltage fast charging power bank to output a certain voltage?

I am trying to power up my raspberry pi 3 with a Xiaomi 10000mAh fast charging power bank through the L298N motor controller. The motor controller can receive from 7 to 35V, and it has a 5v output, ...
0
votes
1answer
712 views

Multiple Input supply switching

I'm looking into designing a power supply for an RPi that can take both USB and battery at the same time, but only pull power from one of the sources. I'm not quite sure how to go about it, I was ...
0
votes
1answer
183 views

Switching between 2 power supplies upon dropping below cutoff voltage efficiently

I am making a circuit which is powered by a lipo battery of 11.1V(3.7V*3). I need to check for the lipo's under-voltage so that the circuit automatically switches to a second lipo when the first one ...
25
votes
4answers
31k views

Considerations in a bench/lab power supply?

I'm looking at adding a low-cost variable power supply to my electronics hobby bench. After years of cobbling together LM317's and LM7805's, it's about time... Considerations: I've found a few ...
53
votes
10answers
89k views

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 ...
17
votes
2answers
31k views

Constant current, constant power and constant impedance loads

Ive been looking for information on constant power, constant current and constant impedance/resistance loads, there's some information about the constant current loads, but very little that really ...
47
votes
3answers
7k views

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 ...
24
votes
3answers
26k views

How do the tiny AC->USB power supplies work?

The iPhone and Kindle both come with tiny power supplies that take in 120v AC and output around 5V at 0.85 to 1 amp. They seem to be too small and light to have a transformer, and generate very little ...