How do they miniaturize a transformer (220V/5V) to fit in a small smartphone charger?

How do they miniaturize this big transformers to fit inside a really small power supply?

I mean, which electronics techniquies allows them to use such small transformer?

In the picture bellow is a heavy and big 220V/12V transformer. When I go shopping for a transformer, those are the smallers I can find to buy. I cannot find those small smartphone power-supply transformers available to buy.

Where I can get them? What's special about them?

If it's not about the transformer, HOW CAN THEY make a 5VDC from a 220VAC in such small chargers?

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That's a 220V/12V transformer (easily find to buy)

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11 Answers

  • Steven
    Lv 7
    8 months ago

    The transformer in your picture is a simple 50/60Hz transformer so it has to have huge inductance to limit the idle current to a few milliamps, which is very difficult on a small transformer even with the smallest magnet wire. By rectifying the 50/60Hz power into DC that powers an 100KHZ to 1MHz oscillator, the voltage and isolation can be done with a pill sized ferrite core transformer with a few turns of wire. A second rectifier then converts the ~100KHz secondary voltage into DC. Capacitor filters are required on both rectifiers. The oscillator chip, rectifiers, tiny transformer and capacitors cost pennies so the whole thing can be sold for a couple dollars. I won't bother to describe more details here.

  • John
    Lv 6
    8 months ago

    There's formula for transformer ,base on core diameter ,turns of the wires and thickness of the wire .If you open a charger you will see diode and resistors ,which the lower the voltage and break it down to less voltages .This will allow to instal small step down transformer to get 3-5-9-12 volts .  

  • LG
    Lv 7
    8 months ago

    This is a 50Hz transformer, so it is NOT for a switchmode power supply. The short answer is that it has so much less power(this one can only deliver 5 watts) to deliver than those big transformers, so it can be smaller.

    The size of a transformer is mainly determined by how much heat it can safely dissapate. Since the windings are typically made with a material that has some resitance(i.e. copper at above superconducting temperatures), more current means larger wires(to reduce resistance) must be used in the windings to reduce the amount of heat produced by the wires, given the same core size, and keep the transformer from overheating. But putting larger wires around the same size core means more of the windings will be far away from the core, having mostly air for a core, and will contribute less and less to the overall inductance of the primary. So larger cores are used to make the windings more effective. A larger core also means less turns of wire can be used to make the same inductance. When the primary excitation/drive voltage goes up, a larger core is needed to keep it out of saturation.  So the whole transformer becomes bigger and heavier when the power levels go up.

    Contrary to what some believe, the flux in a transformer core does NOT go up with increasing load. So this is not why larger cores are typically used in high-power transformers. The transformers in switch-mode power supplies don't require as much inductance in their primaries, so less turns of wire are typically needed. A few tens of turns of fat wire around a comparatively small core are all that is needed to achieve the required inductance. Less turns of wire, combined with the shorter time between cycles, means a smaller core won't saturate at a given excitation voltage.

    If we could use superconductors for the windings, we could probably make a 1KW, 50Hz transformer the size of the one in the picture.  We couldn't go infinite power, however, due to things like electromigration at high current densities.

    Super high power transformers, like the ones used in power substations, typically have oil cooling to facilitate heat dissipation and keep the physical size of the transformer down.

  • 8 months ago

    They use microchips as switchmode power supplies for Voltage conversion.

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  • 8 months ago

    You can get one - as you pointed out, it is inside of the charger for the phone.

  • Vaman
    Lv 7
    8 months ago

    I am not electrical engineer. The size of tranformer depend on the current also. If one needs very high current then the number of turn on the main should be large. You know that a step down transformer has two sets of wire coils. There is one outside and there is one inside. The inside one is called secondary and out side one is the main. One can supply main 220 volts outside. Now the current requirements. Use VI n= vNI. You need v=3 volts, and current mA, then adjust the N ratio. N/n= 220* I/3*mA. Say I=0.5mA.Then we have 220*0.5/3=220*5/30=110/3=34.

    Adjust N/n terms. May be you take I in micro amp. Transformer rating is the maximum current one can draw from the primary terminal.

  • 8 months ago

    Modern power supplies use a switched mode power supply design.

    The transformer can be much smaller because they run at high frequencies (100KHz) instead of 50/60Hz

  • 8 months ago

    The power that can be transmitted by a transformer of a given size depends (in a first approximation - there are a lot of effects coming in once you get to higher frequencies) on the frequency you are pushing through it. The transformer (core) you pictured above is designed to transfer 5 Watts at 50 Hz (the actual voltages will depend on the winding ratio).

    So, instead of running the mains directly through the primary, those converters first run the mains through a rectifier (four small diodes) and a high frequency chopper. That newly created AC is then run through a transformer (for safety) before it's again rectified and regulated. I'm glossing over a lot of stuff here - for example, the transformer is usually part of the regulator. In any case, those converters nowadays run at frequnecies in the MHz range (one cheap example for a 1 MHz DC-DC converter: - and the largest and most expensive part here is the potentiometer to adjust the voltage... . Be aware that this is a low voltage converter - a mains converter would look slightly different, but not really that much larger).

  • 8 months ago

    It uses new circuit that convert 50c/s power into 100KHz power, this way, the transformer can be made into very small in size but still able to provide high ampere 5v.

  • 8 months ago

    Small power, small transformer!

    A transformer works with two coils, primary and secondary.  (You probably know all this stuff.)  The ratio of turns in these coils determines the ratio of AC in the secondary coil.  So if there are 1000 winds in the primary coil but only 100 winds in the secondary coil, you put 220v on the primary and you'll find 2.2v on the secondary.

    These transformers use TINY amounts of power, though.  And that means tiny current, and that means very thin wire will do.  A smartphone charger, I'm guessing, puts out maybe 1a at 5v, or 5 watts.  There are some losses in there, so perhaps it.s 5.5 or 6 watts in.  Let's say 6 watts.  6 watts/220 volts means the current in the primary is 0.027 amps.  Or 27ma (miliamps).

    My wire chart here only goes down to 40 gage wire, which is like 0.010" in diameter, about 3x the diameter of a human hair.  40 gage wire can carry 0.091 amps, three times as much as would be needed, so you could use even narrower wire.  Wire you could hardly see!  That's what phone charger transformers are made of.  So they don't have to be huge.

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