Re: TI-H: Power supply fot TI

To: ti-hardware@lists.ticalc.org
Subject: Re: TI-H: Power supply fot TI
From: tsaimelv@pilot.msu.edu (Mel Tsai)
Date: Thu, 07 Aug 1997 00:53:04 GMT
In-Reply-To: <33E91272.96E9B408@tir.com>
References: <19970806224753.21735.qmail@hotmail.com> <33E91272.96E9B408@tir.com>
Reply-To: ti-hardware@lists.ticalc.org

>> Hello, I'm Richard Piotter an I am working on a TI power pack that
>> would
>> let you run a TI calculator off of a wall outlet so you don't waste
>> your
>> batteries. I found that using a 4.5 volt adapter is best, since it has
>> a
>> bit more power than batteries and the voltage is closer since
>> batteries
>> drain anyway, but I have had problems with the memory getting erased
>> if
>> the power pack is either connected or removed while the calc is on
>> (someone trips on your cord). I found a chip from MAXIM (I forgot the
>> number but I might get it later) that automaticly switches between a
>> power pack and batteries with little or no voltage dropping or
>> surging,
>> but I can only find a 3.3 or a 2.8 volt version. If anyone can find a
>> 4.8 or 5 volt version, I would be very happy. I want to make a test
>> circuit, and I can get almost any MAXIM chip free by requesting a
>> sample
>> of it, but I don't know if they have a 5 volt version, and if they do,
>> I
>> would need the number (MAX####).


Remember, 4 AAA batteries x 1.5 volts = 6 volts, so 4.5 volts may give
you unreliable operation.  If it has a standard low-dropout regulator
inside, I'm surprised if it would work at all on 4.5 volts.

Second, you don't need a chip to perform the brownout protection.  A
diode, some batteries, and a capacitor (you may not need a capacitor)
are all that's needed to protect the memory when the wall adaptor
supply is interrupted.

-Mel

References:

TI-H: Power supply fot TI

From: "Richard Piotter" <richfiles@hotmail.com>

Re: TI-H: Power supply fot TI

From: Damien <reaper@tir.com>