Mobile Phone Chargers.

AN original Nokia charger is rated for 700mA. And the transformer inside it is minuscule. Even my large transformers (iron core) heat up. How are such high capacities achieved.

I understand that ferrite cores reduce eddy loss and thus reduce heating. But small ferrite cores are used only for high frequency transformers. And I am certain that there is no SMPS in the mobile chargers.

To achieve 700mA, a thick copper wire winding in the secondary is required. How are all these features fixed into such a small transformer?

Most newer power adapters actually do have tiny switch mode power supplies in them. They're easy to tell as they're a whole heck of a lot lighter and more efficient (they stay cool) than traditional line frequency power adaptors.

However I sometimes wonder about their reliability...

lord loh. said:

And I am certain that there is no SMPS in the mobile chargers.

Click to expand...

You may be 'certain', but you are completely 100% wrong! - they use SMPS, this makes then small and light.

Here's a little tiny SMPS - 120VAC (USA spec) -> 5V@2A for a USB2 hub. That's a standard T-1 LED and the foreground schottky diode is in a standard TO220 for size comparisons. (#*@#% hub died on me... Grr.)

In the foreground you can see the secondary rectifier diode and low ESR filter caps, the black cap that's on its side is the input filter. I didn't spend too much time figuring out what everything is, but the LP-0520T04 is the flyback transformer, and the switch mode transistor is right behind it on the other heatsink. A filter/PPFC choke is towards the back.

I'm quite surprised they make stuff like this now, but it's about time. There's no way to get 5V @ 2A from a linear this small and weigh so little...

(Oh, as for the reliability aside, I've never had a low frequency transformer+rectifier+linear wall wart die on me, but I've had these small SMPS die on me before... hence questions about reliability.)

Are there any other small, light, high power topology that's not a SMPS? AFAIK I don't think there is, but, I'm curious... Pictures would be nice!