----- Original Message -----
From: James S. Lee <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, 4 August 2000 11:16
Subject: Re: MD: External MD Power Supply for 722
>
> Since I asked this question about the Radio Shack "Portable CD Player
Power
> Pack" (23-505) rechargeable lead battery, I have gone ahead and used it
> with the 722. The unit functions quite well except that the "battery
> charging" indicator never goes out. So it would seem that the internal
> battery is not being charged, at least not effectively. So, does that
mean
> that it is possibly being discharged while the external battery (3 - 4.5
> nominal voltage) is attached?
No I don't think so. The connection between the external batteries and the
internal one would at least have a diode in between to stop inter-action
and I suspect it would be far more complex than that, using the voltage
regulator chip to switch between battery supplies.
The Sharp 701/702 voltage regulator chip is quite smart - it recognises
different voltages from different sources (incl car jack) and controls it
accordingly.
I had the same problem with a RS 4.5v power pack - it would drive the
player but not charge the battery.
In the end I built a 5v regulated supply, using an ic and capacitor and
fed this with 7.5v from the RS power pack. The 5v is rock solid and
charges the battery perfectly.
I have a circuit somewhere if you are interested, thanks to another (can't
remember who) MD-L contributor.
>
> How does the Sharp prioritize battery drain anyway? If, for example, I
have
> the Sharp battery pack installed and a freshly charged internal battery,
> which is the primary current supplier to the unit?
If you have a charged internal cell and the external battery pack fitted
the (701) recorder uses the internal supply first and then changes to the
external supply, without stopping record or playback.
GB
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