Saturday, January 30, 2016

Modifying a dual USB charger socket

I bought a cheap pass-through socket with 2 USB ports from Pollin. The blue LED is too strong at night so I modified it, see below for the "before" and "after" pictures. Obviously, the unit is photographed with the mains socket missing, that's not how it actually ships.

The charger is rated at 1A and in my experience is able to provide more than that. It's actually one of the few non-dedicated chargers in the house that is able charge the iPad without triggering a warning on the screen.

Since it doesn't come [directly] from China it's likely built to a decent standard.

By the way, the part number was "94-351077", but it's not on stock anymore.

 The output is based on a THX202H SMPS regulator with decent specifications. The datasheet for that IC shows a reference circuit for a 5V/1A supply, which is what I guess they used here.

The underside shows quite a bit of rework happening: it looks like most of the SMD parts were manually soldered and the right-side USB socket as well. Judging by the quality of the soldering job I'm worried there might be a few cold joints and solder blobs waiting to fall and short-circuit the board.

Other than that, the separation between mains voltage (240V) and the low voltage side (5V) seems adequate.

The resistor that seems responsible for setting the LED current is R6 with a marking of 102, thus a value of 1 kilo-ohm.

I just desoldered that and put into its place a 10k resistor instead from my parts box. Probably any value between 4.7k and 47k will achieve similar results.

As you can see from the second picture, even with a 10 times less current the LED is still plenty bright.

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