Questions tagged [transformer]

A transformer couples two or more AC signals through a magnetic field. Often used as galvanic isolation and to transform one AC voltage to another.

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71
votes
4answers
105k views

How is using a transformer for isolation safer than directly connecting to the power grid?

How is using a 1:1 transformer safer than using the mains straight off? Is it because you can limit the current coming from the transformer whereas straight from the mains its not current limited? I ...
61
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8answers
35k 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?
59
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3answers
9k views

Is this video fake? I thought Tesla coils only worked on AC

This video shows a 9-volt battery is connected to a wire as a primary. The first reason I think this is fake is that he is powering a Tesla coil with 10 volts. The second reason is that Tesla coils ...
52
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6answers
16k views

Why do transformers use so many turns?

Transformers have hundreds of turns on both the secondary and primary winding, and as a result use very thin copper wires for each. But, why do they not just use fewer turns on each winding and get ...
43
votes
11answers
4k views

Is there a dual of the transformer?

Capacitors and inductors are duals of each other. A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary ...
40
votes
9answers
10k views

How can "purely" electrical circuits emit sound?

Moving membranes or piezoelectric materials obviously produce sound waves, but how can "purely" electrical circuits such as transformers or DCDC choppers (and others) often have an audible noise? Is ...
27
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4answers
5k views

How were four wires replaced with two wires in early telephones?

In this video, when A wanted to talk to B, a microphone was connected to a distant speaker using two wires (A → B). When B talked to A, a copy of above was used in the other direction (B → A) using ...
26
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6answers
4k views

Why do high-voltage transformers need oil?

Someone told me that high-voltage transformers need oil because it prevents arcing. However, in terms of dielectric breakdown, isn't air the strongest? I remember from classes in college that as the ...
22
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4answers
7k views

5 V home network

I'm planning on adding multiple IoT devices in my house, and I'm looking for an elegant solution to power them all. They'll all need 5 V, a small number of them (cameras) would draw up to 2 ...
22
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4answers
34k views

What is the difference between a transformer and a coupled inductor?

Transformers and coupled inductors seem very similar. Is there a difference in construction? Or only in use? This question asks something similar, but the answers don't address my question: Coupled ...
21
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3answers
96k views

How to transform 5 V into 12 V?

I would like to transform 5 V 500 mA (from USB power) into 12 V with a few cheap components. Is this possible with the help of some generic parts (and not with the help of some expensive transformer, ...
20
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3answers
6k views

Can roles of primary and secondary windings be reversed?

Is there a practical reason that the roles of the primary and secondary of a simple single-phase transformer cannot be swapped? Say you have a transformer (from the old vacuum tube days) that has ...
20
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2answers
2k views

Power supply - purpose of the capacitor on the side of the transformer before full bridge rectifier

I was wondering if someone can explain the purpose of the capacitor C1141 from the attached picture. I know that C1142 is a filter cap: that much is obvious to me. However, I can't seem to grasp the ...
20
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2answers
12k views

How do I use a transformer as an inductor?

Lp: Self inductance of the primary winding. Ls: Self inductance of the secondary winding. Lm: Mutual inductance between the primary and secondary windings. Assume that I need an iron core inductor ...
19
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3answers
3k views

Why do travel transformers have a setting for either 50W or 1600W?

I've noticed this "feature" on a number of travel-oriented voltage converters - they either are meant to be used for small 50W loads, OR for larger loads up to 1600W. But you can't run a ...
18
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7answers
6k views

Why don't three-phase transformers use toroidal cores?

When looking at different transformer core designs, three phased, I never see any core designed as a circle or torus. Why is that so? Will it not work as well as the common B-shaped core?
18
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4answers
11k views

Why don't AC transformers burn up

I'm marginally familiar with the way that an AC transformer works. After viewing this question: Why don't all motors burn up instantly? It got me thinking about the same thing with AC ...
18
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4answers
12k views

Cellphone charger has no transformer?

I opened up a really tiny mobile phone charger I have, to see how it is designed. The entire "charger" is integrated into a small 2-pin mains plug, 1 x 1.25 x 0.5 inch, that has an USB socket for the ...
18
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3answers
2k views

How critical is winding a solenoid/electromagnet neatly?

We've all seen the expensive toroidal winding machines on YouTube, and manufactured solenoids are always so neat in construction - as in: Each winding is neatly packed to its previous, without ...
18
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7answers
2k views

What precisely is the numerical (or any) meaning of mutual inductance and, is it useful, representative (of something) or important?

When we consider two inductors that are magnetically coupled, we sometimes talk about mutual inductance. As an example, consider two inductors (such as 9 μH and 4 μH) that are 100% coupled and produce ...
18
votes
1answer
11k views

How do these new-fangled phone chargers achieve step-down?

There appear to be two kinds of power supply adapters in market. The first/older kinds were such that they were reasonably heavy and had a small transformer inside the adapter itself. The newer ones ...
18
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2answers
38k views

How does this mosquito zapper circuit work?

For the purpose of learning, I have tear down a small mosquito zapper racket. I am now trying to understand how the circuit is working (which goal is to produce high voltage). (yellow = resistor, ...
17
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2answers
27k views

What happens if I connect a transformer in reverse?

I was thinking the other day. A transformer is just two coils, right? There is no polarisation or anything else fancy? The ratio of the number of windings on the input to the number of windings to the ...
17
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3answers
36k views

Why does LTSpice say that my "Matrix is singular" for this ideal-transformer circuit?

I'm trying to do find the voltage over R1 in the following circuit, where L1/L2 is an ideal transformer. LTSpice complains that the "Matrix is singular". Why? I've tried to play around with lots of ...
16
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2answers
2k views

How to calculate air gap in flyback transformer?

I’m designing (or at least trying to design) a flyback converter on LM3478. I chose the EFD20/10/7-3F3 core [1]. Using a PDF from Infineon [2] I calculated that I need a primary winding inductance of ...
16
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3answers
134k views

What does 40VA rating for transformer mean?

I am working on a circuit for a home make home security system. I bought the following wall transformer to power my circuit. I was going to use with a 5VDC Linear voltage regulator to get 5 volts for ...
16
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4answers
3k views

Is this a safe way to measure mains power on an oscilloscope?

I wanted to use my cheap battery powered single-channel oscilloscope or my Rigol 1054Z to see the 120V AC mains signal in my house. No particular reason, just curious. I at least knew enough to not ...
15
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3answers
2k views

What is the purpose of transformers on the output side of a DC power suppply?

I have a PSU that plugs into 220-240V AC mains (L&N, no ground) and outputs 9V DC to a single barrel plug. On the barrel plug side, just about 10cm before it, there's a little box on the cable ...
15
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4answers
6k views

What are the effective power limitations of the flyback converter topology, and why?

Looking at several different isolated converter topologies, flyback looks like it's the simplest at first glance. There's only one switch, so there's only one driver, which (all other things being ...
14
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4answers
2k views

Does the number of turns in Turns Ratio matter in transformers?

Suppose we have two transformers with same turns ratio, \$N_2/N_1\$. First transformer \$A\$ is of \$100:10\$ and the second transformer \$B\$ is \$1000:100\$. Both have same turns ratio so both can ...
14
votes
3answers
74k views

Why do thunderstorms knock out power?

It isn't like lightning strikes the wires. And surely the whole apparatus is designed to be water-proof. So what is it that causes power outages during thunderstorms?
14
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2answers
3k views

What is the purpose of putting a capacitor on the primary side of a step-down transformer?

I'm looking at this design For a split supply. I get that the thermistors are there to limit the inrush current, but I don't understand the purpose of C9 and how its value was chosen.
14
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2answers
3k views

Why does this isolation transformer have another transformer in it?

The isolation transformer I'm looking at: http://www.mouser.com/ds/2/336/HX1188NL-515471.pdf My question is why is it there? Is it not enough to have just the transformer on the left?
14
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3answers
30k views

Difference between current transformers and power transformers

In a current transformer, the primary current causes a magnetic field in the core, which in turn generates a current in the secondary. Fine. How come then that a power transformer outputs a voltage,...
14
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3answers
5k views

Why do underground cables "require a higher degree of reactive power compensation" than overhead lines?

I was reading a brag sheet for a certain company's giant transformers, and I came across this sentence: Furthermore, in some regions, the existing over head lines are being replaced by underground ...
14
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3answers
107k views

How to determine which wire is which on a transformer?

Let's say I have a transformer with 3 coils. When primary coil is connected to 230V, two secondaries output 12V. Wires are color coded, but I don't know what colors stand for and there is no ...
14
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1answer
1k views

What does a black bar across transformer symbol designate?

What does a black bar across a transformer symbol designate? This appears in a power electronics context, and in particular in this case with substituting a DC transformer as an equivalent circuit ...
13
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5answers
4k views

Can a transformer work if the core is not circular?

I am trying to build a transformer to convert 12V AC power to 5V AC. Here is what I have right now: I haven't adjusted the coil ratio yet but I tried it just to see if there would be any output and ...
13
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4answers
64k views

Why does a delta/wye transformer make 30 degrees phase shift ?

I'v heard that a delta/delta or Wye/Wye transformers do not make any phase shift. In delta/wye or wye/delta transformers, There is a 30 degrees phase shift between the primary and secondary coils. So, ...
13
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2answers
2k views

If I used the primary coil as an inductor, does the secondary coil affect it?

I've read this question. It's about how to obtain the maximum inductance from a transformer: How do I use a transformer as an inductor? Now, I would like to use the primary coil only as an inductor ...
13
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3answers
32k views

What is a Class 2 Transformer

I need to replace a damaged 120V-12V transformer that is a European sourced Comelit Model 542012/A, also marked as "Class 2 Transformer" supplying power to a halogen table lamp. My question is what is ...
12
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2answers
1k views

Why are the transformer windings in series with line and load in this circuit?

I came across this switching power supply circuit and I noticed the transformer is connected in a way I had never seen before. What is the benefit of connecting it like that? And why does the circuit ...
12
votes
3answers
17k views

How are neon sign transformers built?

I'm aware that neon sign transformers (NSTs?) produce high voltage - up to 15kv. But I cannot picture what's inside of one. Wikipedia seems to indicate that they may be a form of resonant ...
11
votes
3answers
9k views

Why do laptops need larger transformers than mobile phones?

I was wondering why a laptop power adapter is so huge. Most laptops that I have seen use a ~19V power supply. Using transformer equation, and considering 100 turns in the primary(just an assumption), ...
11
votes
4answers
5k 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 ...
11
votes
9answers
7k views

how can I make a large transformer less loud?

I have a large 2600W 230V -> 28V transformer, and it makes a constant quite loud bzzzzzz sound while it works. Is there any way to make it more silent (other then buying an equivalent SMPS which I don'...
11
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2answers
3k views

What is the use of transformers with 3 pairs of wires?

I found a device which has a ferrite core and 3 coils on it. It looks like some type of transformer. What would be its use? I found it in a compact fluorescent lamp.
11
votes
5answers
22k views

Minimum number of turns on a transformer

I am trying to wind my own transformer for a power supply. How many turns do I need on my primary winding? I know that the turn ratio determines the voltage ratio, but how do I determine the actual ...
11
votes
3answers
3k views

What to do about very hot planar inductor?

What I'm doing: I am designing a DCDC converter to generate ±24v from an incoming supply of 18v - 36v. For this I am using the TI TPS54160, and following the document Create a Split Rail Power Supply ...
10
votes
4answers
39k views

Using a transformer to step down 230V to 12V

My circuit uses main electricity in parts of the circuit. However my AVR and other components only need 5V. So I'm using a step down transformer to generate 12V. It's then regulated to 5V. The ...

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