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Subject: Re: Archos Car Adapter

Re: Archos Car Adapter

From: Manuel Dejonghe <>
Date: Sat, 12 Feb 2005 00:26:32 +0100

you're always welcome.
I dunno why, but I felt somehow that I was explaining more than needed :-)

Well, if you are techie by profession, you've had much more education
in that area that I have.

Nevertheless I think you must have been measuring something wrong. I
don't think ANY electronic circuit is able to get too hot to touch it
with bare hands by draining 70 mA at 12 V (assumed), 0,84 Watts if I'm
not barking up the completely wrong tree here. That would be something
like the invention of a new power source.
If the regulator circuit is REALLY draining solely 70mA to your power
supply/car, maybe then your circuit is draining somehow power by the
archos ?
This will certainly show up as soon as you measure the current flow
between l4940 and your archos.

There is another thing I just think of, that I could think of could
apply if you connected by mistake a RecorderV2 to the circuit.
For the RecorderV1 (charging control done in software) the charging
current to the batteries (thus power drain) rises WITH the voltage.
The v2 (charging control done in hardware, so maybe completely
different, and maybe I'm on the woodway again) has a far lower power
rating (6V instead of 10-12V). So the circuit would deliver far too
high voltage (which should in second be limited by a second regulator
inside the archos) and the charging control MAY even drain more power
than expected.

Regards, Manuel

On Fri, 11 Feb 2005 17:02:08 -0600, Tom Clemmer <> wrote:
> Thanks for the response. I measured the input current to the regulator at
> 70mA but I might have not done that right. I am an electronic Tech by
> schooling but have not done that type of work for some years. I have lots
> of soldering experience,so I don't think I fried the regulator. I did by
> two when I bought it.
> Thanks again and I will look at joining the list.
> Tom
> ----- Original Message -----
> From: "Manuel Dejonghe" <>
> To: "Tom Clemmer" <>; "Rockbox development"
> <>
> Sent: Friday, February 11, 2005 4:35 PM
> Subject: Re: Archos Car Adapter
> Hi Tom,
> I didn't expect feedback from that article so soon :-)
> There are three reasons why I post this on the rockbox-mailinglist as well:
> - documentation. I would not like to write the same info a second time
> if somebody else asks next month :-)
> - knowledge: maybe somebody else has another idea.
> - correction: maybe somebody else on this list reveals I got no clue
> about electronics.
> I strongly recommend you to get subscribed on the list. You will be
> able to reply to everybody, and you will get anybodies answer,
> independently of the fact wheter they forgot to add you to the list of
> recipients or not.
> Well, in the meantime, I read the papers (specs of the 4940) more
> throughfully, and thought I should've taken the V12 one, as the low
> voltage behaviour is better than I expected, but thats another story.
> I first wanted to wait to see how mine behaves before adding info to
> the article. My fear was that 10V could be a small bit to weak to
> charge properly, but it does just very well.
> So, now to your problem:
> No, mine is not getting very hot at all. I tested a few times by
> holding the small package in my hand after having an half an
> hour-travel (that the most I am doing at the moment) and it was so
> cold I could not determine if it comes from ambient temperature or
> not. The black brick I mounted on it is merely a buffer than a
> heatsink as well. Else I wouldn't have it packaged (and thus
> preventing from cooling) with the thermo-shrink tube. I just mounted
> it (the black block) for security as IF the unit drains more power
> than expected, it would only be for a short while like hard disk power
> up/spin up.
> I know from experience that such voltage regulators are allowed to get
> hot. I've once been told to check the temperature by touching it with
> a wet finger. If it fizzes, it would be too hot. So that shows you
> what temperature regulators are allowed to get, and up to which
> temperature regulators are supposed to work without getting damaged.
> There is two things that may heat up the regulator in regular
> operation: to much power drain or input voltage different from what we
> expected (I assume below 8 volts, or even less, and above 17 volts, as
> the data sheet says)
> Now there are two things that is disturbing me:
> - The first is that yours is getting hot, and not mine. Temperature is
> usually rised if your device drains a lot of power/current (ampere) or
> if the input voltage is higher.
> - The second is, that the voltage regulator is known (or at least
> advertised) to have a very decent temperature controlling. It would
> rather stop delivering that current than burning itself to death. I'm
> just checking the spec sheet to see what may be the cause. I assume
> "too hot to touch it" is above 75 C
> Unfortunately, the data sheet does not have a figure showing the
> result temperature of output current or something like that.
> Now I can think of two things:
> - Either you did not pay attention (I admit, I did not warn in the
> article about that, should add that) to not grill the regulator by
> assembling it. I absolutely don't know how long it should be exposed
> to which temperatures during soldering. The data sheet says the max is
> 150 C, but this is certainly for a longer time, as I know I soldered
> it with 300-350C. I've been teached to always pay attention with
> diodes, transistors, triacs and so on (in general, all
> semi-conductors) to not over-heat them, but I've seen people handling
> them I would've bet they broke it, and it worked, so maybe it's not
> that sensible my vater taught me. I actually never killed any
> component during soldering by accident.
> - There is more power drain as expected. If there would be a
> short-circuit between regulator and archos-device, you would not tell
> me it would be working very well, as there would be no current
> arriving at the archos anymore. So the only one thing I can imagine
> of, is that something in the archos broke so in trains more power
> somewhere, most probably a loose contact then.
> So I definitely recommend you to measure the load/draining current of
> the archos as well. Most probably, it will not drain more than 600 mA
> in ANY case.
> Unfortunately, I got not enough practical experience, to be able to
> predict anything.
> I hope that helps, Manuel (lImbus on irc)
> On Fri, 11 Feb 2005 14:02:11 -0600, Tom Clemmer <>
> wrote:
> > Manual,
> >
> > Thanks for the write up in the car adapter using an l4940V10. I finished
> > mine and everything measures good. When I power the Archos, the L4940
> gets
> > very very hot, too hot to touch. Now I do not have a heatsink on it but
> was
> > wondering if your was getting very hot as well?
> >
> > Tom

Received on 2005-02-12

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