Charger circuitry

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Charles Hawtrey - 03 Jan 2004 22:12 GMT

I'm getting fed up with having to carry separate adapters for my cell
phones and MP3 player and battery charger and radio and everything
else. So I have this idea to build the Mother of All Power Supplies
that could supply whatever voltage and current any particular gizmo
might need. My question here is, how much of a cell phone's charger
circuitry is internal to the phone itself as opposed to being in the
charger (wall wart)? Ideally the intelligent part of the charging
circuitry would be internal to the phone and I could simply furnish a
clean 5V (or whatever other voltage) to the phone.

Thinking specifically of a Motorola P280 and/or a SE T300 but more
general answers would be appreciated as well.

TIA
C.

--
A lie gets halfway around the world before the truth has a chance to
get its pants on, but what was the truth doing with no pants on in the
first place? --Winston Churchill

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Todd Allcock - 04 Jan 2004 07:04 GMT

> I'm getting fed up with having to carry separate adapters for my cell
> phones and MP3 player and battery charger and radio and everything
[quoted text clipped - 11 lines]
> TIA
> C.

In my experience the intelligence is always in the phone. Since those
cheapy non-OEM car chargers that sell on eBay for $1 don't melt phones, how
much intelligence can Hong Kong put in a 12V charger that sells for 50-cents
wholesale? ;-)

I've used those Radioshack "universal AC adapters" with selectable voltages
and plugs in a pinch and haven't melted anything yet (except for one old
Casio PDA that I fried when I accidentally had the output switched to 12VDC
instead of the desired 4.5V. Only took about 3 seconds- I noticed the usual
green charging LED flared an angry orange then went dark, never to light
again!) :-(

The Nokia phones are the weirdest- they'll take any voltage from 3V to 9V
and the phone seems to deal with it. Different models of Nokia charger for
the same phone will output wildly differing voltages. (My "real" Nokia 3650
charger puts out 7.7VDC, the Nokia OEM car charger outputs 9+, and my old
Nokia 8290 AC charger outputs 3.7V and all charge the 3650 and 8290 equally
well!)

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gopi - 04 Jan 2004 08:39 GMT

> Thinking specifically of a Motorola P280 and/or a SE T300 but more
> general answers would be appreciated as well.

I'm fairly confident that with any modern lithium-ion based charger,
it's all in the phone. The charging circuitry needs to know the
capacity of the battery - most phones can take a few types - the
temperature of the battery, and measure its current voltage.

The Motorola P280 and similar can charge from your USB port with
regulated 5v (abusing the USB spec of course); the modern Ericsson
connector just has 5v on it as well. Ericsson headsets are also
straight 5v.

Safety issues and practicality pretty much require an advanced link
between the charging circuitry and the battery, guaranteeing that the
charging circuitry is in the phone.

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Karen - 04 Jan 2004 13:59 GMT

The battery/power management intelligence is in the phone, however, the
charger has a current limiting device (probably a simple diode). The power
management circuitry has more to do with current than voltage, that is why
some phones (Nokia, et. al.) can accept a wide range of input voltages.

> > Thinking specifically of a Motorola P280 and/or a SE T300 but more
> > general answers would be appreciated as well.
[quoted text clipped - 12 lines]
> between the charging circuitry and the battery, guaranteeing that the
> charging circuitry is in the phone.

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Fashion sense - 09 Jan 2004 00:32 GMT

This is simple. Go to Best Buy, or similar, and buy a variable wall-wart AC
to DC adapter, with variable adapters. I carry one of these around. It's got
a switch on the side that varies the DC output and a set of varied connector
plugs.

> I'm getting fed up with having to carry separate adapters for my cell
> phones and MP3 player and battery charger and radio and everything
[quoted text clipped - 16 lines]
> get its pants on, but what was the truth doing with no pants on in the
> first place? --Winston Churchill

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dan SCHEIN - 09 Jan 2004 12:11 GMT

> This is simple. Go to Best Buy, or similar, and buy a variable
> wall-wart AC to DC adapter, with variable adapters. I carry one of
> these around. It's got a switch on the side that varies the DC output
> and a set of varied connector plugs.

They work well and you can even buy mobile (12 volt) models. The problem
seems to be finding adapters for cell phones. Thats a roll your own
project.

Signature

dan SCHEIN
http://www.dschein.com

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