Idle question: Square or Sine wave for transformer? - Page 1
Forum section: electronics / beginners

author: apelly
author_rank: Unknown
timestamp: February 08, 2016, 12:13:24 am
content: I was just reading another thread, and I was wondering. Are transformers more efficient driven with a square wave or a sine wave?You want maximum flux as soon as possible, changing as fast as possible. The core size and composition effects how fast and how much the flux can change.It seems like you should jam all your electrons it at once on a sharp edge.Am I thinking (and talking) out of my arse?

author: Dave
author_rank: Super Contributor
timestamp: February 08, 2016, 12:57:19 am
content: Well, a square wave is really just a bunch of sines on top of each other.Here's the thing, a transformer is going to be most efficient at one particular frequency. If you only feed it a single tone at that frequency, it is surely going to more efficient than putting in higher harmonics, which aren't going to be transferred to the other side as efficiently.Bear in mind that this is just the fruit of my thought process, putting 1 and 1 together, I haven't actually researched this.

author: Vgkid
author_rank: Super Contributor
timestamp: February 08, 2016, 01:00:43 am
content: Wouldn't putting a square wave into a transformer give you a lc time constant pulse as the output. I have never actually messed with this.

author: rx8pilot
author_rank: Super Contributor
timestamp: February 08, 2016, 01:13:24 am
content: I would think the transformer would turn it into a more of a sine wave and the 'destroyed' harmonics would be turned into heat.Never tried it.

author: apelly
author_rank: Unknown
timestamp: February 08, 2016, 01:23:12 am
content: Quote from: Dave on February 08, 2016, 12:57:19 amThat is true.Quote from: Dave on February 08, 2016, 12:57:19 amAlso true. And determined by the core.Quote from: Dave on February 08, 2016, 12:57:19 amNot sure. The tone doesn't transfer. The field does.The core doesn't saturate immediately. More energy should cause faster saturation, no? Sure, we have no influence over how quickly it collapses. Or does the load effect this?Anyway, there's surely no benefit in providing power as the field collapses? That's half of a cycle wasted.

author: apelly
author_rank: Unknown
timestamp: February 08, 2016, 01:28:36 am
content: Quote from: rx8pilot on February 08, 2016, 01:13:24 amI agree the output is going to look sinusoidal.Now I'm thinking that the efficiency is coming from the magnetic field resisting current flow. Therefore it makes no sense to to drive it faster than the core magnetises.I think I agree with you.

author: VK5RC
author_rank: Unknown
timestamp: February 08, 2016, 04:13:13 am
content: I tend to think of a transformer as two close coupled inductors, the higher frequency harmonics of the square wave just won't 'get in' ie too high an impedance presented by transformer.

author: apelly
author_rank: Unknown
timestamp: February 08, 2016, 04:22:28 am
content: Quote from: VK5RC on February 08, 2016, 04:13:13 amThat's how I was thinking too.Quote from: VK5RC on February 08, 2016, 04:13:13 amOnly after the magnetic field is established. Prior to that it's just a piece of wire.Of course, as I said earlier, I'm only guessing. I'll google it later I suppose. I could just do some experiments, but unfortunately all my kit is unavailable temporarily.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 08, 2016, 06:23:36 am
content: Losses generally increase with frequency, so yes, sine is more efficient.The difference is small for most designs.Switching converters don't have much choice, of course!Tim

author: Seekonk
author_rank: Super Contributor
timestamp: February 08, 2016, 08:11:16 am
content: I have a 60z transformer that is operating at300Hz square waves, it was expedient to do so. The core clearly heats up and the windings stay cool. Transformer was designed for a MSW converter.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 08, 2016, 02:32:00 pm
content: Quote from: Dave on February 08, 2016, 12:57:19 amAlmost correct. A square wave is actually a sine wave of the same frequency but with all of the ODD-harmonics of that frequency added in. The magnitude of each odd harmonic decreases as the frequency rises. Adding the odd-harmonics "files In" the corners of the sine wave to make it a square wave.Long story short, a 60 Hz square wave will contain a 60 Hz sine wave, a 180 Hz sine wave, a 300Hz sine wave, etc, etc etc. Transformers tend to work only a specific frequency so the they won't react well the 180Hz and the other high frequencies. The harmonics will be mostly filtered out and generate heating in the transformer. The transformer output will be 60 Hz with few if any of the harmonics so it will be a nearly pure sine wave.Note: transformers can be built to have wide frequency range, for example for audio use, but power transformers are usually designed for a specific frequency and will sharply attenuate other frequencies.

author: bobcat
author_rank: Regular Contributor
timestamp: February 08, 2016, 04:07:44 pm
content: Actually, the secondary will give spikes generated during the rise/fall of the square wave of current through the primary.See Jeri Ellsworth's video demonstrating this:https://youtu.be/1tAyvafIv04

author: fubar.gr
author_rank: Unknown
timestamp: February 08, 2016, 04:55:14 pm
content: Another way to look at it, is that passing a square pulse through a traffo is essentially similar to passing DC. The core will saturate and the primary winding will become a short circuit.But if the pulse duration is short enough (frequency is high enough), so that the core has no time to saturate, the traffo will work ok, as long as the core has no significant iron losses at that frequency.This is essentially how SMPS transformers and signal transformers (eg. Ethernet) work.

author: Dave
author_rank: Super Contributor
timestamp: February 08, 2016, 05:31:42 pm
content: Quote from: Stray Electron on February 08, 2016, 02:32:00 pmSoooo... which part of your explanation invalidates my statement?