----- Original Message -----
From: Dan Michaels <oricom@USWEST.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, October 30, 2000 11:47 PM
Subject: Re: [OT]:MAX232 line driver


> At 10:36 PM 10/30/00 EST, you wrote:
> >Hi Group,
> >
> >I am using one of the RS-232 drivers on the Maxim MAX232 to generate
 a -9V
> >source voltage.  The -9V out is tied into a 79L05 to get -5V out.
> >
> >There are 4 caps that are used along with the chip.  These can range in
value
> >from 0.1uF to several uF.
> >
> >How does the value of the caps come into play in regards to driver
current?
> >Is the more the better?
> >
>
> Probably, but even so, you really cannot draw very much current
> off of the MAX232 pins. Looking at the curves, you will see that
> the effective output resistance of the -V line is on the order of
> 300-400 ohms. It only takes a few mA to drag it down to where
> the 79L05 will no longer regulate.
>

And the 79L05's quiescent current will gobble up quite a few of those
precious milliamps.

You might want to look for a low-drop-out, low-quiescent-current regulator,
you'll get a lot more usable milliamps.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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