37
votes
Accepted
Does this AC to DC + breadboard setup have the ability to kill/severely hurt me?
These can be good. They're usually good.
You don't need to guess about quality.
You only need to consider the source, and look at the markings to see if it has the mark of an NRTL (Nationally ...
29
votes
Accepted
Computer power supplies usually have higher efficiency on 230V than on 115V. Why?
As the law \$ P = U * I\$ , to acheive the same power at lower voltage, you need to increase the current.
In resistive components, like wires, pcb traces, transformer wire (green), losses increase to ...
- 8,144
26
votes
Is it possible to step down 240 AC to 5 DC without transformer?
Capacitive power supply circuits have been used for decades in things like alarm clocks, small appliances (coffee makers) and the like. They work pretty well for small constant loads without the bulk ...
- 47k
26
votes
Accepted
How do phone chargers have variable input voltage with constant output voltage?
Modern AC-DC power supplies do the voltage conversion in three steps. Roughly speaking, the process is as follows.
First, they rectify the AC into DC, so 100 V AC gets into about 140 V DC, and 240 V ...
- 42.4k
23
votes
Accepted
Which power source is good for my project?
The first circuit - capacitive dropper - is totally unsafe, it has a direct connection to the mains. I'm not going to comment on that circuit further, except to note that several important component ...
- 174k
20
votes
Accepted
Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?
Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?
Yes it probably can - the initial worry is saturation problems due to operating at the lower frequency but, with the voltage dropping to 180 V ...
- 473k
20
votes
Computer power supplies usually have higher efficiency on 230V than on 115V. Why?
As Oskar Skog proposed, the power factor corrector (PFC) is the main suspect.
The PFC is usually a precisely controlled boost converter that converts the pulsating rectified mains to something like ...
- 9,686
19
votes
Accepted
Second opinion on PCB design for relay made in Altium
In addition to what has already been said:
One neat trick (...from the 1980s) is to place through-hole resistors vertically so that they don't take up as much board space. You shouldn't have ...
- 22.3k
17
votes
Accepted
Replace x2 capacitor with polyfilm?
...can I use that (polyfilm (myler) capacitor) instead of an X2?
No.
There's a reason for that and that reason is safety. Especially in a (mains connected) power supply you want to take safety ...
- 81.4k
16
votes
Accepted
Bridge rectifier: 4 diodes vs. single chip?
Can't believe I wrote all that crap about diodes...
MUR860 will indeed sound better, but the explanation is a bit subtle:
Silicon diodes do not turn off instantly. As the voltage across the diode ...
- 82k
15
votes
Is this circuit safe to put in my ceiling? What improvements could I make?
Definitely not safe by any metric.
There is no fuse or other manufacturer suggested mains voltage protection circuits befoe the mains supplies.
The outputs of the supplies are shorted together without ...
- 172k
14
votes
Why is this power adapter transformerless?
That is a capacitive dropper supply as others have said, but I am going to take a slightly different view of the things safety.....
Iff it is built right into the torch such that no part of the torch ...
- 17.6k
14
votes
Is it possible to step down 240 AC to 5 DC without transformer?
The answer is "yes" - but it is dangerous because there is no isolation and component failure can lead to the full voltage and current from the mains appearing at the output. Here is a ...
- 14.3k
12
votes
In AC/DC adapters, why can't the DC cable be detached from the adapter?
Because it would cost more since you now need two more connectors.
The AC side is detachable because different countries use different outlets.
ADDITION BY HEARTH:
...and the DC side isn't, because ...
- 57.3k
12
votes
How to protect a power supply
It is just a component that can be used to build things.
It is not supposed to be used as-is.
It needs a case around it.
- 172k
12
votes
Predicting health of power supplies
No, you can't tell if it's about to die.
If you are measuring the "good amps" by short-circuiting the output with the meter's ammeter you may hasten the death of both the power supply and ...
- 181k
12
votes
Second opinion on PCB design for relay made in Altium
I haven't looked into every details of it,
but my two cents review comments are:
The lack of mounting holes for screws of some sorts. If you have enough space, do it. It's easier to have holes that ...
- 6,661
11
votes
Strange minimalist power supply, which IC?
"L1" is not an inductor, it's the world's cheapest looking magnetostrictive ultrasonic transducer. The construction is similar to a solenoid or other speaker, but there is a rod of ...
- 29.3k
11
votes
Accepted
Getting a small AC "reference" from a DC power supply?
I can separately find a 6V transformer but that results in an independently isolated AC. (And that's not helpful to me... right?)
Nope.
The simplest way to go is what you said, a separate transformer....
- 23.2k
10
votes
Does this AC to DC + breadboard setup have the ability to kill/severely hurt me?
No. Those wall warts are quite safe. The high voltage input is isolated form the low voltage side by a transformer that steps down the voltage right off the bat to a safe level, and pretty much all ...
- 57.3k
10
votes
Accepted
What are the advantages and disadvantages of feeding DC into an SMPS?
All SMPS that work from a connection to an AC mains supply have a fuse. The fuse prevents the SMPS from catching fire should it fail. The fuse is an important safety device. Using the image provided ...
- 473k
10
votes
Accepted
Is an AC/DC converter with no visible fuse before the transformer inherently dangerous?
It's probably fine.
There's normally no fuse as such in the old wallwarts with the big transformers like you have.
There's normally a fusible link inside the windings on the primary side. The fusible ...
- 73.6k
9
votes
Is DC-to-DC (24 V to 12 V) buck conversion typically more efficient than AC-to-DC (110 V to 12 V) conversion?
No general statements can be given.
Generally, the larger the input/output voltage ratio is, the smaller the efficiency for basically all converter topologies.
However, whether you end up with 70%, ...
- 100k
9
votes
Can I safely turn a standard computer PSU into a 220VAC to 36VDC converter?
No - it's not doable.
The computer PSUs typically have a single 12V output rail, and so all 12V outputs are in parallel.
You can't connect 12V outputs in series to make a 36V supply, you would short ...
- 172k
8
votes
How do phone chargers have variable input voltage with constant output voltage?
If you want to identify one 'component' that's responsible for the constant output voltage, then it's the 'feedback'.
The forward path which includes the flyback transformer pushes a controllable ...
- 174k
8
votes
How can low voltage, low-current power be efficiently extracted from mains?
Transformers can have very high efficiency- higher than switch mode supplies. Transformers are quite different from resistors; transformers can convert one voltage to another at high efficiency (high ...
- 7,865
8
votes
Having trouble understanding textbook explanation of "hot chassis" in full-wave voltage doubler vs half-wave
A better way to say it would be "the output is common-ground with the source".
Hot Chassis
This term was relevant back in the Bad Old Days, when electronic equipment was allowed to be mains ...
- 45.8k
7
votes
Why is this power adapter transformerless?
Most countries require that devices not conduct any significant amount of current between either of the mains supply leads and any exposed metal surface, even when a significant potential difference (...
- 47.3k
7
votes
Compact on board AC to 5VDC converter
You'll find hundreds of internal, print-mount, closed frame, open frame, ... power supplies on distributors like digikey.
So, as usual, a single property, in this case supply size, is seldom the ...
- 100k
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