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There is a transformer in this 127V AC to 5V DC Converter. I am trying to get one of them. But I don't know what kind of transformer is and I am unable to find it in my city. enter image description here

Also, it is so small. When I ask in the local electronics shops about a transformer capable of converting 127 V to 5 V. They give me a very big transformer. So I don't know how it is possible that this little transformer do the same. The circuit specifications are these:

enter image description here

Thanks

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  • \$\begingroup\$ That's the only component I am unable to find. And I think it is very interesting that you can use transformers that small for applications like these. So I want to know exactly what it is. Because if I know what it is, then I would be able to use smaller transformers and make PCBs that I designed smaller and lighter \$\endgroup\$ – Delfin Feb 7 at 3:36
  • \$\begingroup\$ I am not going to buy it yet. For the moment, I just want to know how that circuit works. And what component is that. \$\endgroup\$ – Delfin Feb 7 at 3:41
  • \$\begingroup\$ Maybe I need to change the question for: How this converter works? \$\endgroup\$ – Delfin Feb 7 at 3:44
  • \$\begingroup\$ This is isolated flyback converter. \$\endgroup\$ – Eugene K Feb 11 at 20:16
  • \$\begingroup\$ Is not a buck converter? \$\endgroup\$ – Delfin Feb 11 at 23:25
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Check the two black electrolytic caps on the left in your first picture. Are they rated for about 400 - 450 volts?

If so, what you have is an input rectifier which will produce a high DC voltage at the caps. The transformer is then part of a switch-mode power supply which is effectively a DC-DC converter which converts high voltage to low. Also known as a buck converter.

Something you'll need to learn about transformers is that the higher the operating frequency the smaller the transformer needs to be for a given power level. So, as Michael Karas answered, the transformer will operate at about 200 kHz rather than 50-60 Hz,and can be much smaller than a transformer which operates at line frequency.

And why 200 kHz, you ask? It's part of a compromise. While increasing the switching frequency reduces the size of the magnetics, it also increases the power dissipated in the switching device, usually a MOSFET. So, depending on the exact circuit and construction, switching power supplies usually run at about 100 kHz (more or less), where the value of the continued shrinkage will be outweighed by the increased power dissipation of the switch. The exact frequency will depend on exactly what circuit is used, what components are selected, what voltage/current combination is specified, the temperature limits on the circuit, emitted RFI issues, and a bunch of other considerations.

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  • \$\begingroup\$ Yes, they are labeled as: 400V 10uF. So, the capacitors rectify the signal? \$\endgroup\$ – Delfin Feb 7 at 4:12
  • \$\begingroup\$ Probably it is important to mention that there are more components on the back of the PCB. There is one called ABS10 .. It is very small too, But I think that is the one that rectifies the signal \$\endgroup\$ – Delfin Feb 7 at 4:14
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    \$\begingroup\$ @Delfin The capacitors don't rectify it, the diodes do. The capacitors just give you a hint at what's going on, because if it wasn't some kind of switching converter you wouldn't need those capacitors. \$\endgroup\$ – Hearth Feb 7 at 4:24
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    \$\begingroup\$ @Delfin - No, the caps store energy after the input has been rectified by something else. I can't see enough of the board to identify the rectifier. \$\endgroup\$ – WhatRoughBeast Feb 7 at 4:25
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    \$\begingroup\$ @Delfin - "The rectifier is at the back of the PBC." Maybe it is, maybe it isn't. I'm not sure you know what to look for. And since you did not realize that capacitors are not rectifiers, I'm not going to take your word for it. And neither should you. \$\endgroup\$ – WhatRoughBeast Feb 7 at 4:28
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Instead of looking for a transformer you should be searching for a PCB mount switching power supply module.

5V at 2A is a ten watt unit and can be found. If you are looking for repair replacement then your challenge will be to find one with same form and fit.

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  • \$\begingroup\$ But what kind of transformer is it?. Normal transformers are not that small. I am just looking to understand how these little converters work \$\endgroup\$ – Delfin Feb 7 at 2:57
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    \$\begingroup\$ Your first photo is a DC-DC converter, or switch-mode power supply. As marked on the transformer, the supply operates at 200 KHz - a transformer operating at that frequency requires much less iron (or a much smaller core) that one operating at 50 or 60 Hz. You are very unlikely to find a replacement transformer, as that one was almost certainly custom designed for that power supply. \$\endgroup\$ – Peter Bennett Feb 7 at 3:00
  • \$\begingroup\$ Is not a DC-DC Converter. It is an AC-DC Converter. The second photo shows the case where the circuit was inside. And it says: Input: 100-240V ~ 50-60 Hz, Output: 5V 2A max. In Mexico, we use 127 V AC at 60 Hz \$\endgroup\$ – Delfin Feb 7 at 3:32

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