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I was at the dollar store (dollar tree) today and this "dual USB car charger for dc 12v-24v" cigarette lighter adapter deallie caught my eye. Naturally I was weary about plugging something like my phone or tom tom into something from the dollar store, so I bought one to investigate. I was guessing "they" would be using a linear regulator, or perhaps something really messed up like some diodes, but to my surprise the thing contains a legit buck SMPS. Also surprisingly "they" did not scratch off the part number. Output with a light load, a boarduino since it is next to my computer and has power I can easily probe, was 5.2 volts. So for a dollar you get a convenient 5 volt 1 amp smps you can throw at things you would typically stick a 7805 on. Or I donno, charge your ipod or whatever. Curiosities include no screws, a plus for me since you can open it very easily, and the "port a" being for an ipod which I'm guessing has something to do with the extra resistors on the data pins. I would call it a great deal for tinkering, costing way less than something like a regulator breakout board
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
That chip is very easy to use, it might struggle a bit with 1 A output since the internal transistor is not very high current. It is possible to use it to drive an external transistor. There is a nice calculator for it here:
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
That is a great find. What held the case half-shells together? It could replace a 78/9 xx regulator but the switching noise might be a hassle for radio experiments. One use for stuff like this is to kit out experiments for continuing ed. or high school. Schools have no money these days. The itenerant instructor can land a contract by building lesson plans around courses in which all hands-on materials are furnished in the price. Using the AN for that chip and that gadget, a short course in sm regulators could be built. boost,buck and inverting.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
yeah, i get a lot of these from car boot sales because the phone they were purchased for broke or was lost; another source is defunct flatbed scanners.
interestingly the mc34063 can be paralleled if the output voltages are balanced to within 0.2%, easily done with resistors. outputs then combined using low drop diodes, so 5 in parallel gives whatever voltage at 5A.
it worked when I built one...
advantage is that instead of one chip running red hot at 1.4A, two chips can be run at 0.7A and reliability can be improved.
as for the noise, this can to some extent be reduced by lowering the switching frequency and locking the oscillators together, this technique is used on some stepper drivers.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
Let me add that the MC34063 can easily be upgraded by using external switching components such as a PNP bipolar transistor or even a MOSFET device. TIP135 may be a bit slow but just the right guy for the job. Swap it for a TIP42 to improve switching characteristics and the 5A region should be no problem. Evaluation circuits are shown in the datasheet.
the complementary types to the two transistors mentioned above are nice performers for these applications, too. The inclined circuit designer may want to go for the mosfet circuits.
Registered Member #2648
Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291
I wonder what the quiescent/standby current is like. Apprently some USB chargers have a bad quiescent current and can flatten your batteries if left plugged in.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
I could not find a "dollar USB" charger but at the Thrift Shop among their collection of wall warts there were two coiled cord cigar lighter chargers/adapters. 50 cents each.
One used the 34063 and the other used the 7500B (16 pin) with the 2SA1020 transistor and all had app notes on the net. The 16 pin regulator had smt caps and Rs on the back. The curly cord is 2 wire with various end connectors. For pocket change they are a good source of prime parts,
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dollar store USB car charger
