# Where to find SMALL POWER TRANSFORMERS?

#### Dan Aronin

Joined Dec 14, 2018
37
Hi all, I'm interested in assembling a circuit that will be capable of CONVERTING 220V TO 5V@2A 10W (Edit: AC TO DC)

The issue is that I manage to find only PRICEY, HUGE TRANSFORMERS like this.

I know there are small circuit (example) available for purchase, so my question is -

Where can I find the small power transformers like they use?
Or maybe they step up current in circuit?

THANK YOU FOR ALL SUGGESTIONS!

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#### kubeek

Joined Sep 20, 2005
5,736
The second link is a switch mode power supply, so it works on a much higher frequency of about 100kHz instead of 50Hz for your normal transformer, so the transformer can be much smaller and still transfer 10W.
Such a power supply is definitely not a project for beginer, so I suggest you either buy something already available or bite the bullet and use the standard 50Hz big heavy transformer.

#### Dan Aronin

Joined Dec 14, 2018
37
The second link is a switch mode power supply, so it works on a much higher frequency of about 100kHz instead of 50Hz
Thank you so much for replying, I will ask 1 more minute of your time to kindly explain wehther I can use a 100kHz transformer with my outlet power of 220v@50Hz?

#### kubeek

Joined Sep 20, 2005
5,736
Not directly, you need all the circuitry around that is on the module to be able to do it. Also note that there will be a bunch of components on the other side of that pcb too.

#### Dan Aronin

Joined Dec 14, 2018
37
Not directly, you need all the circuitry around that is on the module to be able to do it. Also note that there will be a bunch of components on the other side of that pcb too.
Thanks! Do you have any sources I can read and learn from?

#### bertus

Joined Apr 5, 2008
21,041
Hello,

A SMPS powersupply has a fast switching circuit in it.
I have attached a PDF with some basics from microchip.

Bertus

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#### Dan Aronin

Joined Dec 14, 2018
37

#### Audioguru again

Joined Oct 21, 2019
2,389
You posted the link to a cheap Chinese no-name-brand transformer. Do you trust the 10W spec's and hope that it will not burn down your home? I always buy genuine high quality transformers from Digikey, or from high quality products.

Many electronic products come with a small 5V/2A SMPS like you want. People give them to thrift stores who sell them cheaply.
I found a few that people leave on the curb for recycling pickup day.
I bought a few from an electronics surplus store. Name Brand (Philips) and made for an obsolete router. They had thousands of them for $1.75 each. They also had Name Brand clock radios also for$1.75 each.

#### Dan Aronin

Joined Dec 14, 2018
37
Not directly, you need all the circuitry around that is on the module to be able to do it. Also note that there will be a bunch of components on the other side of that pcb too.
What about transformless power supply? I know it is far more dangerous to mess with...but, will it do the job?

#### Papabravo

Joined Feb 24, 2006
14,864
What about transformless power supply? I know it is far more dangerous to mess with...but, will it do the job?
Maybe..but since they can also kill you, they are a forbidden topic of discussion here.

#### Dan Aronin

Joined Dec 14, 2018
37
So to sum up my home work about power supplies... Switching mode is the cheapest and smallest option available, right?

#### Papabravo

Joined Feb 24, 2006
14,864
So to sum up my home work about power supplies... Switching mode is the cheapest and smallest option available, right?
It is not quite that simple. If you are limited to OTS (Off The Shelf) components, you need to realize that those parts are not optimized for space and weight. they are just producible in large quantities. If you were to order a custom transformer in sufficient quantity, I'll bet you could get significant improvement in size and weight if cost was no object. In fact, if you were to select a core material and make your own you could probably make one that would be an improvement.

#### Tonyr1084

Joined Sep 24, 2015
5,535
HMMMmmmmm. I have 220 VAC and need 5 VDC @ 2A. Well, I suspect you can get a transformer at a hardware store for your doorbell. I happen to have one in the cupboard that runs 110 input to secondary 8VAC (one side of a center tap), 16VAC the other side of the center tap) or 24VAC (ignoring the center tap). I suppose in your area you can probably find a doorbell transformer that will do the job (similar to the secondary voltages), then use a buck converter to drop the voltage down to a regulated 5 VDC. Not the cheapest but not expensive either. And you're getting away from those dangerous voltages. Just be sure to ground the body of the transformer, and maybe put it in a protective projects box. But make sure it's vented so you don't overheat it.

Joined Jul 18, 2013
22,010

#### Dan Aronin

Joined Dec 14, 2018
37
Don't think I've seen a 5V 2A wall wart. The best I've seen is 700 mA (0.7A). Not saying they're not available, just I've not seen one. Actually, come to think of it - I have an ATC power supply on my bench out of an old computer. It has a substantial 5V output as well as 3.3 and 12 V (+ & -). Bulky though for what may be the application in this thread.
Thanks for the effort but a pc power supply is somewhere 10 times bigger than what I look for.

#### dl324

Joined Mar 30, 2015
12,241
Thanks for the effort but a pc power supply is somewhere 10 times bigger than what I look for.
Why not just use a commercially available adapter. I bought a 5V, 4A adapter for $5-6 at a second hand store. I have some 5V 2A adapters that came with Linksys ethernet switches, but I wouldn't trust them to provide 2A. Thread Starter #### Dan Aronin Joined Dec 14, 2018 37 Why not just use a commercially available adapter. I bought a 5V, 4A adapter for$5-6 at a second hand store. I have some 5V 2A adapters that came with Linksys ethernet switches, but I wouldn't trust them to provide 2A.
Thanks for answering! This is just for home work and theory. I'm not looking for ready to use models..

#### dl324

Joined Mar 30, 2015
12,241
This is just for home work and theory. I'm not looking for ready to use models..
Is an AC to AC wall wart adapter acceptable?