ALDI AUTO XS CPL 2054 6/12V charger repair - part burnt IC identification

[synoptica]

Hey all,

I'm trying to resurrect an old Aldi battery charger so I can keep one of my cars on a maintenance charge.

This charger died a while ago, and I finally got around to opening it up, and much of the magic smoke has escaped, mostly in the form of a UC384x PWM controller.

Fortunately, the chip blew its cap off somewhat cleanly and I was able to read UC384 - but not the last number.  I've found an image online of the guts of the unit which have enabled me to ID the blackened resistor, which is one step closer: https://cdn.milwaukee-vtwin.de/attachments/178/178260.jpg (sadly I can't ID the chip here, shown as U3 in the lower left of the image.)

The datasheet for the IC can be found here: https://www.ti.com/lit/gpn/uc2845

On page 3, we can see that the UC3842 and UC3843 offer 100% max duty cycle, so one of these would appear to be my logical choice, however both feature different UVLOs. 

UC3842 features "TURNON AT 16 V, TURNOFF AT 10 V, SUITABLE FOR OFF-LINE APPLICATIONS"
UC3843 features "TURNON AT 8.4 V, TURNOFF AT 7.6 V, SUITABLE FOR DC-DC APPLICATIONS"

Does anyone have any suggestions about how I might go about determining which of these is the unit I need?

Many thanks in advance!

[fzabkar]

What is the rating of the capacitor on the supply pin of the IC?

[synoptica]

What is the rating of the capacitor on the supply pin of the IC?

I just pulled the board out of the unit to check the traces, and I've discovered that it's a bit further gone than I realised - there's not many components on the rear of the board, but looks like a couple of SMD components have been cooked off the board too.

I think  this one is officially beyond repair at this point

[ingalopez]

Hi.
If the topology is that of a Flyback converter, you should use the 50% Duty cycle versions, the 43 or 45. Flybacks are simpler and are almost always used under 150W. There is not a bulky inductor on the rectifier output filter (maybe a small one , for EMI)
About the UVLO, it depends on the type of power supply it uses to start. Typically, if the power is derived from the rectified line (via a hi value resistor), then the wide UVLO version is the choice. The more restricted supply voltage histeresis is used when the chip is fed from a separte (standby) power supply, that may not be the case on a small charger.
Good luck