Questions tagged [ac-dc]

Questions regarding the safe and effecient design and implementation of AC voltage to DC voltage supplies. Typically Mains to some lower DC voltage.

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34
votes
3answers
130k views

Help me understand the relationship between positive, negative, neutral and ground in AC and DC

This question stems from notations on schematics and seemingly conflicting information I'm seeing. I suspect that I'm seeing different vernacular for the same concepts--but I'm in a place where no one'...
33
votes
3answers
6k views

Computer power supplies usually have higher efficiency on 230V than on 115V. Why?

As seen here in the example, this particular power supply (and most others too) has higher efficiency when running on 230V. Given that computer power supplies are usually required to output a ...
32
votes
2answers
1k views

If we could start our electrical grid from scratch with today's technology, which would be the most efficient choice? AC or DC?

Lately, I’ve been reading about the many advantages of HVDC transmission systems for long distance transmission, undersea links, and others. The historical reason of why AC was picked over DC was ...
27
votes
7answers
6k 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 ...
11
votes
4answers
4k views

How do phone chargers have variable input voltage with constant output voltage?

My basic understanding is that a transformer can step down a voltage by the ratio of the primary and secondary windings, since this is a ratio the output is not constant. Thus my question is, how ...
10
votes
3answers
1k views

Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?

I am designing an AC to DC converter. My power source is a single phase synchronous alternator that has a voltage range of 170~260 VAC and a frequency of 40~60 Hz. Can i use a transformer designed on ...
9
votes
8answers
7k views

Is it safe to use a DC power adapter that isn't UL Listed or CSA certified?

I picked up a 9V switching DC adapter from SparkFun a while back, but I've been hesitant to use it because it doesn't have any of the usual "safety" approvals that you normally see on power adapters (...
8
votes
3answers
7k views

Bridge rectifier: 4 diodes vs. single chip?

I notice (among the DIY audio enthusiasts at least) that when it comes time to design a power supply for an amplifier, DAC or whatever that the parts list will inevitably include something like "4 x ...
8
votes
3answers
1k views

Connecting two DC wallwarts in series - to produce dual DC supply

I have two 9 V, 300 mA wallwarts and would like to connect them in series to produce +9 V, 0 V and -9 V. This can be done with two 9 V batteries (as seen below), but can I do this with two non-...
7
votes
2answers
7k views

Is it possible to step down 240 AC to 5 DC without transformer?

Microcontroller which is controlling mains voltage circuit requires 5 volts to operate. Is it realistic to use diode bridge followed by capacitor to straighten the ac wave and then use voltage divider ...
7
votes
2answers
7k views

Purpose of capacitor across transformer in AC-DC power supply? [duplicate]

I have been looking to buy a AC-DC 5v power supply module to power a mains relay in a circuit I am making. I came across a couple of different models on eBay and am trying to understand their basic ...
7
votes
3answers
49k views

AC adapter: Input power vs Output power

When I look at, let's say an iPad AC adapter, the input/output rating on the charger states: Input: 100-240V 0.45A (AC) Output: 5.1V 2.1A (DC) I know that the ...
7
votes
2answers
20k views

Converting universal AC to 3.3v DC @ 0.1A

There's a bunch of topics around this but i haven't found something that fits my requirements. I'd imagine this is a fairly common thing though so any pointers would be appreciated Basically i want ...
6
votes
1answer
751 views

Replace x2 capacitor with polyfilm? [closed]

I have a 12 V power supply that's not working anymore, so I opened it up and checked for faulty components with a multimeter, and I found two of them so far. One was a 1000 µF 25 V electrolytic which ...
6
votes
4answers
976 views

Converting 8V AC to 8V DC - bridge rectifier gets very hot while idling

I am tinkering with an Arduino and recently had to convert 8V AC to 5V DC in order to run it. The project is a custom doorbell, which gets the power from the doorbell transformer (transformer is ...
5
votes
2answers
1k views

Why are PCB-mount AC DC converters so expensive? [closed]

In a thrown-together prototype, I used a few wall warts to get the various voltages I needed. Now, I'm trying to build a cleaner version with a single plug and put it all on a PCB to eliminate my rats ...
5
votes
3answers
711 views

Why AC supply is rectified first before stepping voltage down?

I have opened one of my phone chargers and was trying to understand how it works.. I found IC MB6F just at AC input which came out to be a bridge rectifier. My question is why AC is first rectified ...
5
votes
2answers
4k views

Is PFC compulsory for AC/DC converters 75W and above?

I’m reading the user guide for a Microchip reference design of a 300W AC/DC converter. Section 1.2 starts with these requirements: A conventional SMPS must implement PFC if it draws more than 75 ...
5
votes
2answers
1k views

Blown Capacitor and Bad Zener Diode in a Switching Power Circuit

We have got a few boards with failed power. Some boards went alive after replacing a bad capacitor (swollen can). Some boards went alive after replacing a zener diode (somehow shorted to ground I ...
5
votes
2answers
8k views

Calculating the True Power Factor in non-linear loads

In my circuit I am taking in 60 Hz 120 VAC from the power company and hooking it up to a AC/DC non-linear switching buck converter I am designing. I know that: true power factor = (displacement power ...
4
votes
3answers
3k views

BJT Pre-Regulator

I have a circuit that has an input of 35V peak and I would like to drop the voltage down to 5V 200mA. I was recommend to use a pre-regulator in the following configuration: The good thing is that it ...
4
votes
4answers
422 views

Is DC-to-DC (24 V to 12 V) buck conversion typically more efficient than AC-to-DC (110 V to 12 V) conversion? [closed]

While building an online UPS system, I'm basing the choice to eliminate as many AC inverters from the system as possible because of the assumption that DC-to-DC conversion is more efficient than AC-to-...
4
votes
3answers
137 views

Given the diagram, where do I add/replace a larger capacitor for continued power while bike is stopped?

Following the circuit diagram, included as an image in this guide, where do I replace/add a larger capacitor for continued power while the bike is stopped? My guess is that it should replace the ...
4
votes
1answer
2k views

AC-DC Adapter - Output lower than rating and what's this 'cont' output for?

I have a Canon AC adapter, Model K30321, that I'd like to use in a project. I'm attempting to test the adapter for correct voltage output. Adapter specs: ...
4
votes
1answer
1k views

Can AC/DC conversion losses from solar panels be avoided with a Tesla Powerwall?

(background: I'm just playing with numbers, trying to estimate how many solar panels would be needed to fully supply the energy for a home and 2 Tesla cars) I've been reading up on solar panels and ...
4
votes
1answer
1k views

12V 1A DC input filter

I have to design a power input filter of consumer device. It is powered with desktop AC/DC 12V power supply. Max current consumption - 1A. Device has a full metal enclosure. I am considering putting ...
3
votes
3answers
1k views

Will a fuse improve the safety of my non-isolated buck converter design?

I have a power circuit that implements an AC-to-DC rectifier and a non-isolated buck converter to convert a 120 VAC 60Hz signal to 12V and then a linear voltage regulator to step the 12V down to 5V. ...
3
votes
3answers
256 views

Why aren't non-isolated DC-DC converters made for high wattage applications?

I am new to electronics. I am presently studying DC to DC converters. One thing I noticed is that most of the people are using isolated stepdown converters like half bridge, full bridge, or resonant ...
3
votes
2answers
427 views

Can I use a 20V or 24V to power up a piano that needs 21V? [duplicate]

The power adapter of the piano should be AC/DC 21V, 1.5A. But I can't find in a short time to buy something exactly like that, but I found this options: 20V, 3A or 24V, 3A Can I use one of this to ...
3
votes
2answers
904 views

Fuse for parallel AC/DC power supply

I am designing a system which will use two 12V AC/DC 60W modules (Meanwell IRM-60-12) I would like to protect the system using a fuse. In the case of a parallel design like the one below, should I ...
3
votes
2answers
440 views

What is a simple yet efficient way of converting 12VAC to 5-12VDC?

I am trying to create an LED pool light that works off a 12VAC input. Upon disassembling a similar pool light (Intellibrite), I found that they appear to be using rectifiers and perhaps a few small ...
3
votes
2answers
6k views

BeagleBone Black - power supply sensitivity

I've bought a AC/DC adapter which per its specifications should output 5VDC and deliver 3A. I was going to use this adapter to power my BeagleBone Black (BBB) with. However, when I'm measuring the ...
3
votes
1answer
653 views

Non-isolated Off-line AC to DC Power Supply

I found two very similar designs (ignoring the LDO on the first one) of this type of supply and was curious if one is better than the other and if so why. I guess a 15V zener is slightly more ...
3
votes
4answers
11k views

Making 12V DC from 6V AC

I've got a 1980 Honda XL 185s that has a 6 volt electrical system. The headlight uses a 6V AC, 30 watt bulb powered from the generator. The other lights (tail, blinkers) operate off of the 6 volt ...
3
votes
2answers
4k views

Why have atx power supplies need selector voltage?

I am studying various ATX power supplies schematics and don't understand the need of the voltage selector as switching power supplies work at range of voltages. In most schematics i see the 110V line ...
3
votes
1answer
119 views

Different Wattage Solar Panels for Home [different Voltage/Ampere]

My current solar system for home 12V 100W polycrystalline Solar Panel. 12V 75Ah Lead Acid solar tubular Battery. PWM 12V 10A Solar Charge Controller. 12V Input and 200VA Output Inverter. Current ...
3
votes
1answer
180 views

How to get from 3 phase variable high voltage AC to 230V AC

I already asked all the electricians in my area (at least 7-8) and nobody could help me, so I am asking you. I have a Pelton generator - a type of water powered generator. My output is 3 phase ...
3
votes
1answer
1k views

AC/DC converter problem

EDITED to update diode spec and schematic... I have two failed outside security lights each with PIR circuit with relay to switch 240V AC mains voltage to another circuit which looks to be a simple ...
3
votes
3answers
1k views

Feasibility of very high temperature ac-dc switching power supply

I'm involved in a product design (on the mechanical side, to be clear that I'm not an EE) where we need a very compact ac-dc switching power supply that will take 90-300vac, 50-60hz and output 5 watts ...
2
votes
2answers
559 views

Electrical circuit / transformer in series?

I would like to pull out 5v 3A max in series from an already existing connection from the mains 240v 40A connection. Current circuit: What I would like to implement: What are the possible problems ...
2
votes
1answer
4k views

Does a bridge rectifier care that much for AC frequency?

As I understand it, a bridge rectifier is a set of diodes that play a trick of logic that keeps the polarity positive. So, within the context of a household DC transformer does it matter what the ...
2
votes
2answers
424 views

What is deciding the current of an AC to DC circuit

I'm a beginner, trying to build a power supply based on the sketch below to convert 230V AC to 5V DC. My final aim is to supply precision voltage for Arduino, which I think is 5V 700mA. Here is the ...
2
votes
2answers
3k views

Full Wave Rectifier Efficiency

I was readings this article and extracted from it that "The maximum efficiency of a Full Wave Rectifier is 81.2%". Is that true, or alternatively is there some other fundamental limit on AC/DC ...
2
votes
3answers
2k views

no-load voltage on ac-dc adapter

I recently acquired a toy that uses this transformer: but since I live in a 220V area, I cannot use it directly. I have this generic AC-DC adapter: which in theory is all I need because it has a 4....
2
votes
4answers
203 views

Converting Christmas Village from DC to AC

So this was the year we bought a AC-powered O-gauge Lionel train and a battery-operated village to add to our Christmas tree decor. The problem, the village eats batteries like a kid eats cookies. ...
2
votes
2answers
107 views

What are the safety and device risks associated with not connecting the grounding prong on a 120V AC device?

For example, imagine a device that comes with a 3-prong (grounded) AC plug. What are the risks associated with, for example, plugging this device into a 2-prong extension cord which effectively ...
2
votes
1answer
126 views

Battery charger output power higher than input?

i would like to ask about battery charger i saw at work :) the plate on charger says: Input voltage 3 phase ac Min 400v Nominal 400-415v Max 456v Input current 20A Output 110v DC 9kW 28v DC 3kW ...
2
votes
3answers
5k views

Can I use a 3-wire AC adapter in a DC circuit?

I am reading through the excellent book Make Electronics and am in a chapter that suggests getting an AC adapter, cutting off the connector at the end and stripping the rubber outer coating back to ...
2
votes
1answer
1k views

Why are some AC/DC adapters light while others are heavy?

I was browsing the thrift store and found a nice pair of JBL 2.0 computer speakers, but they lacked a power adapter. They call for a 12V 1A supply. I have a ton of "bricks" lying around, but no 12V ...
2
votes
2answers
657 views

Coil-less AC-DC line regulator

I'm trying to fix an AC-DC line regulator that I have build and doesn't work as expected. I'm trying to convert AC 220V mains to DC 5V 10mA without a transformer. To do this I'm using an 1uF 250VAC ...