# 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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### 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 ...
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 ...
467 views

### How large would be the transformer for converting a lightning into useful electricity?

My dad asked me the oh-so-famous question yesterday: Why can't we harness the electricity from lighting? After explaining to him the impracticalities of this as far as the amount of energy in ...
3k views

### Current transformer and bridge rectifier -- why the diode drop?

I'm building a circuit to measure AC current using a current transformer, which feeds into a microcontroller's ADC for the actual measurement. As the measurement needs to be fairly accurate, the ...
5k views

### How to properly wind a high frequency / high voltage transformer?

Please, is there any practical tip / caveat I should be aware, when winding a high-frequency transformer? I'm used to wind 50/60Hz transformers and they do work ok, but now I'm trying to make a high ...
7k views

### What happens to a transformer if the supply side is shorted?

Suppose I have an industrial plant, where a switchboard is fed through a transformer. The switchboard have only "passive" loads, i.e. they don't contribute with short circuit currents. If ...
1k views

### Transfer power effectively from one coil to another through air

I want to build my own wooden alarm clock. I want the surface to be smooth without any connectors anywhere. My idea is to place one coil beneath the alarm clock, and another pickup coil inside. I ...
22k views

### Is it possible to have a device with metal case and wireless charging?

Recently I encountered the following idea: that a mobile device manufacturer is not interested in including wireless charging in his devices because that prohibits him from using metal cases in the ...
1k views

### Simulate isolation transformer in LTspice

Hi, I am new to simulating transformers with LTspice, and I struggle getting the circuit to function as expected. The source is a three phase TN-S (wye) connected. Then I wanted to add a 1:1 ...
220 views

### How do European to American outlet change frequency?

So for the transforming of voltage, a transformer could get a european outlet from 240 to 120 volts. How do these switch the frequency though, do they have to convert it into DC and then generate a ...
3k views

### How is a transformer working at 10's of MHz designed?

In this answer a switching power supply using a transformer operating at 10's of MHz range to reduce size is mentioned. How would such transformer be designed? Would it still have a plain old design ...
828 views

### Does Tesla coil use near field or far field?

According to Wikipedia a Tesla coil transfers energy (via loose coupling) from one oscillating resonant circuit (the primary) to the other (the secondary) over a number of RF cycles. which I don't ...
9k views

### Dc isolation (transformer?)

I need to isolate the dc input from the dc current inside the circuit (both 9v), in the same way as a 1:1 transformer isolates the AC current inside the circuit from the input AC. I already found out ...
3k views

### Isolation Transformers (Capacitive Coupling)

In my application I have an issue with ground loops and to solve this I require to have devices isolated from their drivers. The system operates with a 13.56MHz signal and a wide bandwidth is not of ...
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### What is going wrong in this circuit which supposedly should step down AC to arduino friendly voltage?

So I'm using this circuit but when adapter output is disconnected and only midpoint terminal of the transformer is connected the Arduino input pin reads some mV. mid point reads perfect 2.5V. What am ...
637 views

### How does this isolation transformer protect user from transients/mains?

I'm looking at a pretty simple overvoltage/transient protection circuit designed to protect users but I don't understand what the transformer is doing. The circuit is designed to protect the output ...
17k views

### Transformer and IC heating in Viper22a SMPS design

I have designed an SMPS using viper22a IC. This gives an output of 9.8V and on adding a 10 ohm load resistor, voltage drops to 9.6V, thus giving an output of almost 10 watts. Here is the circuit that ...
2k views

### Power line voltage out of phase with ambient 60Hz electrical noise - why?

I just bought my first oscilloscope and have been tinkering with the measurement of different signals just to learn the ropes and familiarize myself with the scope. One of the first things I noticed ...
340 views

### Why can't I get any proper arcs out of this flyback transformer?

I salvaged a flyback transformer from an old TV and used it in a single MOSFET driver like this: I used 6 turns of insulated copper wire to make the primary coil with the centre tap and again 6 ...
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### Adding Two Balun Transformers to SA612 Mixer Has No Effect on LO Suppression

I'm experimenting with a SE612 mixer to learn the basis of RF. I read that the mixer can either be single-ended or balanced, and a double-balanced mixer has the best performance in terms of LO-RF ...
94 views

### How to properly select a transformer in terms of thermal rise

I'm trying to reach a decision selecting a small transformer for a task, from an overseas company (which only significant because of the language barrier). I thought the selection would be easy ...
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### Can broken ferrite core be glued and used again?

While trying to disassemble some SMPS transformers for rewinding I have managed to break the ferrite core. I broke the 'arms' of the 'E' half. Also, I found broken core transformers in apparently ...
2k views

### Half bridge voltage waveform not following PWM

I am making a 12 V battery charger getting power from 220V AC. The topology is half bridge with capacitor voltage divider, as shown in the SG3525 datasheet. While initial testing on vero-board, the ...
327 views

### High Power Supply over a distance

I'm working on a project and have been stopped in my tracks part way through. I am designing a system that will power an RC over a distance. So I have a generator, and around 300 meters of cable to a ...
1k views

### Can I detect zero crossing on the transformer's secondary?

In this answer poster uses the rectified secondary's half sines to detect the zero crossings of the mains voltage. Can you do that? I thought there was a phase difference between primary and secondary,...
145 views

### Measuring soil resistivity and estimating soil equivalent resistance in a long distance

I'm trying to size the Neutral to Ground resistor (NGR) in the Wye of a 138 KV to 4160 V Delta-Wye Transformer. In order to find the proper value I have estimated the charging current of the system by ...
2k views

Never though transformers would be so confusing to many - I found about a dozen similar questions here. Adding mine to the pile. Here are the datasheets for 3 Transformers: 750313975, 750313445 and ...
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### Can this example be used for explaining the effect of lamination on power loss in a power transformer?

I'm trying to demonstrate to a group of people how a lamination of the transformer core reduces the power loss due to Eddy currents by not using any complex math. I start with a non-laminated core as ...
354 views

### What's the meaning of this marking on this old transformer?

I'm studying this old power supply, and it has an odd marking on it (probably not, but it is for me). I'm guessing it is: output in the range [-17v, 17v] with the possility of having different input ...
7k views

### Driving high voltage to ultrasonic transducer with Arduino

I'm trying to drive an ultrasonic transducer with an Arduino. I have the arduino putting 40kHz out of pin 10 and I would like to step that up from a 5V square wave to 100Vp-p or anything near there. ...
25k views

### Working of miniature Tesla coil?

Can anyone explain the given circuit. I seem to have done it and its perfectly working. But can someone explain the principle/theory and working behind this circuit from when the switch is turned on.. ...
1k views

### How should I properlly draw on a schematic a shunt going through the center of a toroid coil?

So I'm trying to reverse engineer the schematic for an Avair AV-200CN SWR bridge. Two toroid coils, used for sensing, are mounted on a shunt, so that the shunt goes through the center of the coils. ...
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### How to reduce voltage without using Transformer?

Is there any way to reduce voltage without using transformer? I have a supply of 24 volts AC @ 1500mA (1.5A) and I want to convert it into 6 volts @ 500mA. Because I have to supply the 6 volts to the ...
3k views

### Relevance of Galvanic Isolation of Boost Converters

Flyback Boost converters use a transformer and this setup is still referred to as galvanic isolation. In most use cases, the output voltage is usually orders of magnitude greater than the input, and ...
1k views

### Unknown DC-DC converter topology in ST datasheet

I have found this weird DC-DC converter topology in datasheet of MC34063 from ST. The primary charging is single ended, so at first it seems like flyback, but it has four diodes on the output instead ...
387 views

### Transformer Inductance not taken into account?

When modelling an ideal transformer, why do we not consider the inductance of the primary and secondary windings of the transformer. Wouldn't this inductance affect the current pulled from the source? ...
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### Why don't we have wireless charger in every portable device yet?

Today I found Texas Instruments announced a circuit for wireless charging - Ti BQ51013 Qi receiver controller - all the materials emphasis how tiny, lightweight, portable, efficient and otherwise cool ...
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### Which has less energy loss - AC step up/step down transformers or DC to DC step up/down converters?

In the EE field, AC transformers are constantly talked about. However, I don't hear much of DC to DC converter modules, even though DC is widely used today, mostly in smaller electronics. Both of ...
2k views

### Voltage Balun 1:1

somewhere I have seen that it is possible to build a Balun by using a transformer in the following way: The explanation I have found is that the fact that the ground is only at the primary coil will ...
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### Are there 2D-Transformers?

I need to create a PCB with a transformer on it, and in this case, I unfortunately can't solder on a regular one. I was wondering if there was anything akin to a 2d transformer, or just generally a ...
1k views

### What are these obscure components?

I'm having difficulty identifying these components. I salvaged them from a diy power supply enclosure from a garage sale. Each of the black leads in the image attached to female connectors on the face ...
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### What is this component and where can I find more details?

I would say it is some kind of transformer but it has the same wire girth on both primary and secondary windings and the same loops count. It had the following label: ...
1k views

### Understanding the Apple 1 power supply

I'm trying to understand the schematic of the Apple 1 computer power supply. Nothing surprising at first sight. Two power transformers (117 VAC -> 10 VAC / 117 VAC -> 28 VAC), two diode bridges, and ...
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### Converting 24VAC to 5VDC - Need transformer demystification

I've got an automatic litterbox that 'needs' to be hacked for better control. As it ships, it comes with a 120VAC to 24VAC (300 mA) wall wart that drives the two motors in it. I'm trying not to change ...
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### Understanding the characteristics of a LED driver

I would like to understand the characteristics of a LED driver I have at home. Here is a photo of the label: I never studied LED drivers before. This post, this article, and this document helped a ...
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### High voltage transmission, transformers and Ohm's law

I have difficulties with understanding high voltage transmission and transformers working process. Particularly with this expression: "the higher the transmission line voltage, the smaller the current"...
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### Why are tapped transformers needed in RF amplifier circuits?

I'm not really sure why, but I have seen many different RF circuits in which the input to a transistor is taken from a center tap instead of across the entire secondary, such as this example: Why is ...
664 views

I have a fairly large (several pounds) old wire-wound transformer, which steps down 220V to 110V (or, I suppose any other suitable voltages, but that's the intended use). I don't know the rating of ...