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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61
votes
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?
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 ...
13
votes
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, ...
52
votes
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 ...
7
votes
1answer
2k views

Power LED bed lamp from mains

I'm attempting to build an LED bed lamp that will be powered by 240V mains. The LEDs are these ones which if I use with a 12V supply and have calculated correctly will draw 0.24W each. I plan to use 5 ...
11
votes
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.
8
votes
3answers
32k views

Dots in a transformer symbol

I came across this schematic: What do the dots in the transformer indicate?
0
votes
3answers
372 views

Transformer, how the primary current is adjusted to be equal to the secondary load (without considering magnetizing current)?

I am happy to always not understand how does a transformer works ... One answer give me 10 questions ... (So I suggest you to not answer to this question, if you do not want to have more questions :D) ...
18
votes
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 ...
22
votes
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 ...
3
votes
4answers
1k views

Magnetic field strength and flux density from hysteresis curve

I am trying to measure the magnetic hysteresis curve of a toroidal nanocrystalline ferromagnetic transformer core made of Nanoperm (datasheet linked) using the following circuit. Each of the windings ...
2
votes
3answers
877 views

Transformer for Flyback power supply

I am designing an isolated DC-DC converter with an input of 12V and an output of 5V@12A, at the moment, a flyback seems like the best option. I have read several books regarding the subject and I am ...
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 ...
21
votes
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, ...
6
votes
4answers
3k views

How does a transformer transmit power from the primary to the secondary?

I'm trying to get my head wrapped around transformer operation and in the process regretting the times I snoozed in my Electromagnetics class as a EE student back when I was a lad :) I'm looking for ...
9
votes
3answers
4k views

Practical way to generate 1500V?

Designing the power supply for an radiation detector, need to supply up to 1500V at 2 mA from mains (170 Vdc). I've largely considered a flyback converter, but cannot find a flyback transformer with ...
8
votes
3answers
22k views

Question regarding use of low voltage high current outputs

I see every day high voltage, high current; high voltage, low current. I rarely see low voltage, high current; why? I know that I can take a high voltage, high current signal, send it through a step-...
8
votes
2answers
21k views

Why is neutral wire connected to ground at the transformer?

I understand the use of ground wire at the home appliances but why is the neutral wire connected to ground at the transformer? Why doesn't the neutral wire go back to the power generation plants. I ...
0
votes
2answers
5k views

How does the secondary coil of a transformer affect the primary coil? How is it in case of Step-up and step-down transformer? Does it obey Lenz's law?

What changes will (of voltage, current, energy, power, etc) happen to the Primary coil, if an AC supply given to the primary coil, but; Secondary coil circuit is turned OFF (Open), Secondary coil ...
8
votes
6answers
46k views

What causes old power supplies to start humming?

I have a number of mains-powered devices that have begun humming (I assume at 50Hz, though I haven't measured it). These include clock radios, a speaker system, a lamp (20W halogen with a transformer ...
8
votes
2answers
4k views

Isolation transformer and scope when troubleshooting SMPS

I have a simple question, when troubleshooting a SMPS is highly adviced to use an Isolation transformer. But my question is this, if im using a scope to troubleshoot the "hot" side of my SMPS, both ...
7
votes
4answers
51k views

Transformer primary and secondary voltage phase shift

If we apply a voltage at the primary terminals of a transformer then for this we can get a voltage at the secondary. But they have 180 degree phase difference. What is the reason behind this?? I ...
4
votes
2answers
4k views

How do I design a current transformer?

I want to make a Current transformer using toroidal ferrites to measure 220/50-60Hz AC current(40A max). Is it possible? And how can I calculate secondary turns count? Ferrite properties: H = 2000, ...
5
votes
4answers
1k views

Why Does DC Load Draw Twice As Much AC Current Through Transformer?

I have designed the following circuit, comprised of 4 loads, 1 of 4.2ohms and 3 of 21ohms, drawing a total of 2.4Arms (1.5A, 300mA, 300mA and 300mA respectively) of AC current through the secondary of ...
5
votes
1answer
5k views

What is the percent impedance of a typical residential power line transformer?

Power transformers are rated by percent impedance. A 5% transformer, when loaded to full spec secondary current, will show a ~5% deviation from nominal output voltage. What is the percent impedance ...
7
votes
3answers
6k views

What are the bare minimum parts needed to operate a magnetron?

I recently took apart a microwave, and I managed to get a magnetron out of it, as well as a transformer that appears to be the power source for the magnetron, but looks a little small for the ...
3
votes
2answers
7k views

Connecting center-tapped transformer to earth ground; or, why am I being electrocuted?

Silly question here. I've wired up a full-wave rectifier using this dual-secondary transformer. If you want to check my wiring, I connected red-to-orange to "create" the center tap (I assume this is ...
1
vote
1answer
122 views

Buffering the input to a passive RC integrator used to measure magnetic flux density

Note: this is part of a larger question which I was asked to separate into subquestions. Other subquestions: 1 and 2 I'm using the method outlined here to measure the induced magnetic flux density in ...
1
vote
0answers
79 views

Scaling of magnetic field strength and flux density measurements and shape of hysteresis loop

Note: this is part of a larger question which I was asked to separate into subquestions. Other subquestions: 1 and 2 I'm using the method outlined here to measure the induced magnetic flux density in ...
0
votes
3answers
12k views

Toroidal Core Calculation

Few days ago I got sample of toroidal core from my friend. I don't know any technical details of core just know OD-10cm, ID-6cm, height- 5cm and wet about 1.845 kg(M4 grade CRGO). I want to make ...
0
votes
0answers
148 views

Cutoff frequency of passive RC integrator used to measure magnetic flux density

Note: this is part of a larger question which I was asked to separate into subquestions. Other subquestions: 1 and 2 I am using a passive RC integrator to measure the induced magnetic flux density in ...
0
votes
1answer
383 views

How to correctly use the formula for calculating the air-gap in a pulse transformer?

To achieve a certain value of the magnetizing inductance (Lm), we can adjust the transformer air gap. Air gap calculation formula: There is no particular information on this, but I assumed that: <...
7
votes
5answers
44k views

If a step-up transformer increases voltage, then how current can be decreased ? is really the current in output is smaller?

If a step-up transformer increases voltage, then how current can be decreased ? If a step-up transformer increases voltage, then how current can be decreased ? (I'm trying to ask that, in case-of ...
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 ...
10
votes
3answers
14k views

How is transition from three-phase distribution without neutral to three-phase consumption with neutral achieved?

A typical distribution grid supplies 6 or 10 kilovolts AC to a substation near the consumers. This is typically done with a three-phase line without neutral - just three wires going in parallel. Then ...
10
votes
4answers
14k views

Square Wave input into Transformer

Can a square wave generated using an astable NE555 be used as input of a transformer instead of AC? Say, I generate a square wave of 60Hz using NE555 and a 24V at 6A supply and feed it into a ...
10
votes
7answers
119k views

Why does the USA use 110V and UK use 230-240V?

Why does the USA use 110V and UK use 230-240V? What are the advantages? Explain me with calculation. Why do they use different frequencies like 50Hz, 60Hz? What is the reason?
2
votes
5answers
5k views

How can the infinite reactance of either primary or secondary in an ideal transformer draw current?

Assumption 1: An "ideal" transformer is said to have very large primary, secondary, and mutual reactance.. (self-inductance/mutual-inductance tending toward infinity), has a unity coupling coefficient ...
9
votes
3answers
5k views

How to dimension a power supply transformer?

I always hesitate when dimensioning a transformer for a DC power supply, and I guess I sometimes overdimension them. My confusion stems from the difference in transformer and DC voltage. If I need 10V ...
6
votes
7answers
62k views

How can I calculate the inductance of the primary of a transformer given a specific load on the secondary?

Inductance in the primary of a transformer decreases as the load on the secondary increases. How can I calculate the inductance of the primary coil? What if it was step up or one to one ratio?
3
votes
2answers
818 views

smps transformer capacitance effects

What are effects of interwinding capacitance in smps power transformer? What is the influence? For example, i have 83khz smps transformer with windings made of litz wire. The capacitance between ...
12
votes
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 ...
8
votes
3answers
5k views

Is it okay to connect a European 240V transformer to a US 240V outlet?

I've an old Bosch German made automotive charger transformer with ratings 14V/9V, 220-250V @ 50/60Hz 132VA. Can I use it on the 220 to 240V outlet here in the US which uses a split - phase system as ...
7
votes
4answers
3k views

How does a wireless charger work without a magnetic core passing through both "coils"?

Every time I hear the description of a wireless charging system it goes like this: "remember a transformer? It's the same here - one coil is in the base and another is in the device and when you put ...
6
votes
4answers
3k views

How can we have high voltage and low current (in transformers), if V = I * Impedance?

I have researched a lot on this topic (including this site) and found this link somewhat helpful : How is it possible to have high voltage and low current? ...     But still it seems ...
4
votes
3answers
2k views

Small-signal model of flyback converter

I am trying to derive the equation of small signal vout/d for a CCM flyback converter. In order to do this, I need the small-signal average model. I am having difficulty seeing how the small signal ...
3
votes
3answers
15k views

In a single-phase transformer output, which-wire would be phase, and which-one would be neutral?

In a single-phase transformer input, one wire getting entry as live, another as neutral. But what would be in case of its output? In output, which-wire would be phase, and which-one would be neutral? ...
1
vote
2answers
18k views

Why is HV kept open in OC test of transformer?

Why is HV kept open in OC test of transformer? Also, why is LV shorted in SC test of the transformer? (Generally this is preferred - why?)
20
votes
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 ...
8
votes
1answer
730 views

Why does short distance wireless energy transfer have such low efficiency?

Wikipedia and numerous other sources cite the following statement about Magne Charge high-power inductive charging system: For example, the Magne Charge system employed high-frequency induction to ...

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