Design Article
Cell-phone charger: nice idea, bad implementation
Patrick Mannion
11/26/2012 10:38 AM EST
Now and again you come across a device that’s so simple, useful, and functional that you’re glad to add it to your already-overladen workbag; that is, until it breaks, for the dumbest of design reasons. In this case, I am talking about a cheap USB power connector.
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I got one of these devices a while back. It’s a simple cell-phone backup battery from a no-name Chinese company that was a show giveaway from a well-known IC manufacturer. While the idea was good, from a marketing standpoint, it’s ironic that no parts from that company can be found inside. Instead, the main part comes from Texas Instruments, in the form of the LM324 operational amplifier, along with a USB power detector and battery-charging circuitry.
I may need your help ID’ing some of the other components, but a hulking—relative to the size of the board—inductor, as well as a 220-μF, 16V electrolytic capacitor tell me that U1 (labeled DK J8) may be the output transistor for a low-frequency switching power circuit.
In any case, it’s a classic case of a useful device gone bad: A poorly designed mini-USB input power port came detached right when I needed it most. Now the device is useless, unless I can get it soldered on again. Given the size of the solder positions and their location under the connector, a fix does not seem likely. Suggestions for how to do that are welcome. For now, it’s an interesting lesson for anyone who thinks the MCU or processor is the most important part of an advanced system. All reverts to naught when the connector breaks!
How often have you seen good devices or designs fail because of silly corner-cutting? Send your photos and story to patrick.mannion@ubm.com; we have to do a collection of these!
Also see:
- Teardown: Inside the Apple iPhone 5
- High-res pressure sensor brings stair-track capability to Fitbit Ultra
- Welcoming the son of iPad–introducing the iPad Mini
- Teardown: Inside Given Technology's Pillcam Colon 2
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duanebenson
11/27/2012 7:37 PM EST
Maybe cut open a short mini-USB cable and solder it in as a dongle with a lot of hot glue for strain relief.
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patrick.mannion
11/27/2012 10:00 PM EST
Hey Duane, that might do the trick! Just need to steady my hand and I'm all set :)
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DugW
12/5/2012 12:20 PM EST
Give yourself some room, solder extension conductors to the board (there appears to be a lot of realestate there), flip then connector on it's back attach your extensions and anchor the connecter with a strong RTV (Dirko). Rigid mounting will cause stress elsewhere on the board.
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grantb3
11/28/2012 1:48 PM EST
Hopefully one of the ICs is a regulator ... otherwise the output is probably not the expected 5v.
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Mike Capoccia
11/29/2012 6:17 PM EST
I am suprised. It has been a while since I opened up an item like this. I used to run a hybrind circuit board line for a major manufacuterer in Southern California. (28 years ago). One question? Is it now standard operationg procedure to NOT conformal coat these things? A good conformal coating provides a load path that may have well prevented this. Pretty darn cheap too.
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WKetel
11/30/2012 4:08 PM EST
If you are able to solder the connector back in place, adding a bit of good epoxy to anchor the connector body to the circuit board could keep it working for a while. I have always wondered why some folks seem to believe that a very small patch of PCB trace is that strong of an anchor.
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Moviela
12/9/2012 9:36 PM EST
I am thinking it is better to have a couple of spare OEM battries in my dity bag. It is false economy to not have enough battery with you in the field.
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Radio Randy
1/7/2013 3:02 PM EST
I'm thinking that 220uf capacitor could use a little solder, as well. Looking at both sides of the board, I can't see solder on either side...must have globbed a little into the plated through holes.
I once tore a pair of computer speakers apart to fix an intermittent issue. The assembler used his/her soldering iron as a paintbrush to apply the solder...what a nightmare.
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Steve Se
1/10/2013 12:14 PM EST
In my opinion, cell phones are another example where incremental designs have moved backwards in terms of utility and functionality. How can I say that with the introduction of smart phones? I am not referring to the relative intelligence in the phone, but rather the charger connector.
My first two cell phones, acquired and retired well over a decade ago, included a charging “cradle”. At the end of the day, I simply dropped the phone in the cradle and simple gravity acting on the mass of the phone made reliable connections between the charging circuit and the battery in the phone.
With each successive generation of phone I have owned since, the charger connector seems to be getting smaller and more difficult to properly align.
Oh I am sure there is a driver for abandoning the charging cradle – it is probably driven by cost. That same connector now serves as an I/O connector for data or a head set to allow hands free conversation. Eliminating a dedicated connector for the charger probably reduced the cost by 30 cents or so, and when you make 10+ million phone a year, that is a lot of cost savings.
But there is no question that the utility of cell phones has suffered as a result. I often finding it necessary to turn on a table lamp to increase the room illumination enough to see which side of the connector is up to allow mating.
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prestone
3/20/2013 6:50 PM EDT
I love seeing super cheap 2-layer PCBs in teardowns, rather than high-end fine-pitch multilayer substrates. It's like the difference between wild-caught seafood and farm-raised seafood.
Anyway, I believe that you're looking at a boost converter on the backside of the PCB. The FET (SOT-223 pkg) has a slightly mysterious connection to the output rail, (perhaps for a built-in freewheel diode) but otherwise it's a textbook implementation. It looks like the battery gets charged directly from the input USB port, presumably up to 5 V. But as it depletes down to, say, 3 V, you still need to keep 5 V on your output port. Enter the boost converter!
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