Can you arrange to have a series FET instead of the diode, turn on the
FET only when the external supply is low.

Sherpa doug

> -----Original Message-----
> From: Graham North [mailto:grahamnorth@CASTLEGROUP.CO.UK]
> Sent: Friday, November 09, 2001 3:38 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [ee]: Low volt drop diode?
>
>
> Hi all,
>
> I have a problem.  On a battery powered instrument I have got
> a diode in
> the line from the
> batteries to the switching regulators. This diode is there so
> that when
> an external power
> supply is connected to the unit, it does not charge the batteries (The
> external power supply
> is connected straight to the switching regulators when plugged in).
>
> Sorry, tried to draw this in asci art.
>
> The problem is this:
>
> There is a drop of approx 0.8 Volts accross the (schottky) diode. This
> limits the life of the
> batteries, as the regulators 'drop out'  0.8 V earlier than they could
> do.
>
> Is there a better way to do this??????
>
> Thanks
>
> Graham North
>
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