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
137k 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'...
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 ...
5
votes
3answers
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 ...
7
votes
2answers
9k 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 ...
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-...
3
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 ...
1
vote
4answers
2k views

home socket with DC voltage

I'm wondering why, in a standard house, instead of using many low power AC-DC rectifier, there isn't a big (like 12V 20~50A) AC-DC rectifier which supplies some wall socket with a DC voltage? In the ...
0
votes
3answers
4k 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 ...
35
votes
4answers
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 ...
6
votes
4answers
1k 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 ...
9
votes
3answers
10k 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 ...
5
votes
2answers
5k 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 ...
9
votes
8answers
8k 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 (...
5
votes
3answers
1k 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 ...
3
votes
1answer
3k views

wiring AC switch with DC led

This is a follow up to a previous question I had answered. I'd like to show the following diagram. Here, I have laid out (crudely) a diagram that has 120v-110vAC from the wall going to a push button ...
1
vote
2answers
2k views

How to design a AC-DC circuit using only the hot/live wire has power input?

I was looking at these new IOT devices coming from CN that are designed to replace your standard wall switch with an ESP8266 smart-switch. It seems there are two types: A) the typical one where the ...
0
votes
2answers
211 views

how to transform 120V AC to 5V DC 5A load using flyback transformer circuit? Setting frequency - low cost, low footprint - change load capacity

i am using a flyback transformer circuit to keep the footprint small and cost efficient. Its been suggested to me to keep the frequency high so the transformer can remain small. how is the frequency ...
4
votes
2answers
3k 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: ...
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
2answers
135 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 ...
1
vote
2answers
750 views

What are design considerations for grounding an enclosed AC-to-DC converter?

Here I'm talking about a device that takes 100-240V AC in, and outputs 10-20V DC out. In terms of grounding, I'm referring to the grounding offered by a standard outlet (e.g., a NEMA-5-15R receptacle)....
0
votes
2answers
1k views

Why are laptops grounded to earth via 1E6 ohm resistance and desktops not?

I measured a few laptop AC-to-DC adapters. 1E6 ohm between GND pin (goes into the laptop) and earth prong (into the wall). Desktops are grounded directly to earth: 0 ohm. Why this difference?
0
votes
1answer
945 views

Understanding LED driver circuit AC to DC conversion

I am recently working on mains socket outlet type LEDs lights. They all have very similar AC to DC conversion circuit. simulate this circuit – Schematic created using CircuitLab C1 is a X-2 ...
0
votes
1answer
687 views

SMPS 5V without load, fluctuation on load TOP258PN [closed]

I am using PI Expert Online (this) to design a smps circuit for 5V, 2.5A output. I already have TOP258PN IC with me so built circuit for that. Change from schematics: I am not using choke and using ...
0
votes
2answers
1k views

Simple circuit to detect ac power loss and use dc backup? [closed]

I want to make a simple circuit like those used in commercial emergency lights. I would have a "walmart" AC to DC adapter powering say a DC light or two. I would like it so when the AC powering the ...
0
votes
3answers
302 views

Power Supply for two 50V/12.5A Solenoids

I'm in the planning stages of building a custom pinball table and one of the sticking points is powering the flipper coils. They're 50V DC coils with a resistance of only 4 ohms during the stroke. ...
-1
votes
1answer
1k views

Connecting two DC voltage sources in series

I need a 42 volt DC supply to check a motor. All I have is one 30V DC source and a few rated lower than this. Is it possible for me to connect the 30V source and a 12V source in series to get the ...
-1
votes
2answers
621 views

sensing the existance of the AC power line [duplicate]

I have more than one AC power source and I want to detect which one of them is ON which one is OFF using a Microcontroller. So my question here is what is the cheapest and smallest in size method to ...