> Hi,
>
> I need to add simple amplifier to my digital system which is powered
> from a single 5V battery.
> To achieve proper operation of the operational amplifier I need at least
> +8V and -8V voltages.
> I can build a simple voltage multiplier and inverter like shown here:
> http://upload.wikimedia.org/wikipedia/en/thumb/b/ba/Stacked_Villard_cascade.svg/400px-Stacked_Villard_cascade.svg.png
> using the 6-CMOS inverter chip as an oscillator and a source of alternating
> voltage.
>
> However antoher idea is to use something cheap and standard like MAX232.
> Has anybody tried to use this chip just as a voltage converter?
> Unfortunately I can't find the output characteristics for V+ and V- pins.
> Maybe I'll need also additional voltage regulator to improve the quality of
> this power supply voltage (or maybe simple RC filter will be sufficient...).
>
> Has anybody tried to do it?
I've done way worse.
These days I prefer a TI TPS60403. Cheap
and less noise.
Reply by Andrew Smallshaw●November 8, 20092009-11-08
On 2009-11-07, boB <bob@bob.bob> wrote:
>
> I like the ST232A because its rails are
> a bit higher than other RS232 chips.
I like it because it is dirt cheap. Last time I needed fairly
small quantities of an RS232 driver the ST232 was 70-odd pence a
peice. The MAX232 was around four or five times that as I remember.
That's a big premium simply for the brand name genuine part.
--
Andrew Smallshaw
andrews@sdf.lonestar.org
Reply by boB●November 7, 20092009-11-07
David Brown wrote:
> wzab wrote:
>> Hi,
>>
>> I need to add simple amplifier to my digital system which is powered
>> from a single 5V battery.
>> To achieve proper operation of the operational amplifier I need at least
>> +8V and -8V voltages.
>> I can build a simple voltage multiplier and inverter like shown here:
>> http://upload.wikimedia.org/wikipedia/en/thumb/b/ba/Stacked_Villard_cascade.svg/400px-Stacked_Villard_cascade.svg.png
>>
>> using the 6-CMOS inverter chip as an oscillator and a source of
>> alternating
>> voltage.
>>
>> However antoher idea is to use something cheap and standard like MAX232.
>> Has anybody tried to use this chip just as a voltage converter?
>> Unfortunately I can't find the output characteristics for V+ and V- pins.
>> Maybe I'll need also additional voltage regulator to improve the
>> quality of
>> this power supply voltage (or maybe simple RC filter will be
>> sufficient...).
>>
>> Has anybody tried to do it?
>
> Be careful you don't overload these supplies. Be especially careful if
> you are using one of the many "equivalent" parts - they vary somewhat in
> how much current they can supply, and what happens if you overload them.
> In some cases, the charge pump switches off on overload and stays off
> until you power off the device.
I do this. ST232A powers an LM393 dual comparator that helps the
receiver do some things it normally won't do, like, add hysteresis, etc.
So far it seems to work great. I like the ST232A because its rails are
a bit higher than other RS232 chips.
boB
Reply by David Brown●October 12, 20092009-10-12
wzab wrote:
> Hi,
>
> I need to add simple amplifier to my digital system which is powered
> from a single 5V battery.
> To achieve proper operation of the operational amplifier I need at least
> +8V and -8V voltages.
> I can build a simple voltage multiplier and inverter like shown here:
> http://upload.wikimedia.org/wikipedia/en/thumb/b/ba/Stacked_Villard_cascade.svg/400px-Stacked_Villard_cascade.svg.png
> using the 6-CMOS inverter chip as an oscillator and a source of alternating
> voltage.
>
> However antoher idea is to use something cheap and standard like MAX232.
> Has anybody tried to use this chip just as a voltage converter?
> Unfortunately I can't find the output characteristics for V+ and V- pins.
> Maybe I'll need also additional voltage regulator to improve the quality of
> this power supply voltage (or maybe simple RC filter will be sufficient...).
>
> Has anybody tried to do it?
Be careful you don't overload these supplies. Be especially careful if
you are using one of the many "equivalent" parts - they vary somewhat in
how much current they can supply, and what happens if you overload them.
In some cases, the charge pump switches off on overload and stays off
until you power off the device.
Reply by Vladimir Vassilevsky●October 11, 20092009-10-11
wzab wrote:
> Hi,
>
> I need to add simple amplifier to my digital system which is powered
> from a single 5V battery.
> To achieve proper operation of the operational amplifier I need at least
> +8V and -8V voltages.
> However antoher idea is to use something cheap and standard like MAX232.
> Has anybody tried to use this chip just as a voltage converter?
Yes, this works. However, it delivers only few milliamps and the output
is very noisy.
> Unfortunately I can't find the output characteristics for V+ and V- pins.
> Maybe I'll need also additional voltage regulator to improve the quality of
> this power supply voltage (or maybe simple RC filter will be sufficient...).
That depends on your application.
> Has anybody tried to do it?
This is a pretty standard trick.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Reply by wzab●October 11, 20092009-10-11
On Oct 11, 4:50=A0pm, "TTman" <someone...@ntlworld.com> wrote:
>
> The max 232 will give you 10 mA max..
Thank you very much.
Now I have also found it in the "OUTPUT VOLTAGE vs. LOAD CURRENT"
chart on the 4th page
of the http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf
datasheet.
And in fact such use of MAX232 is accepted by the manufacturer.
However yet another question is the voltage quality.
I suppose, that the clock signal driving the charge pump will be also
present in the output voltage.
What is a typical frequency of this clock?
--
TIA & Regards,
WZab
Reply by TTman●October 11, 20092009-10-11
"wzab" <wzab@ise.pw.edu.pl> wrote in message
news:slrnhd3rfr.tmi.wzab@wzab.nasz.dom...
> Hi,
>
> I need to add simple amplifier to my digital system which is powered
> from a single 5V battery.
> To achieve proper operation of the operational amplifier I need at least
> +8V and -8V voltages.
> I can build a simple voltage multiplier and inverter like shown here:
> http://upload.wikimedia.org/wikipedia/en/thumb/b/ba/Stacked_Villard_cascade.svg/400px-Stacked_Villard_cascade.svg.png
> using the 6-CMOS inverter chip as an oscillator and a source of
> alternating
> voltage.
>
> However antoher idea is to use something cheap and standard like MAX232.
> Has anybody tried to use this chip just as a voltage converter?
> Unfortunately I can't find the output characteristics for V+ and V- pins.
> Maybe I'll need also additional voltage regulator to improve the quality
> of
> this power supply voltage (or maybe simple RC filter will be
> sufficient...).
>
> Has anybody tried to do it?
> --
The max 232 will give you 10 mA max..
Reply by wzab●October 11, 20092009-10-11
Hi,
I need to add simple amplifier to my digital system which is powered
from a single 5V battery.
To achieve proper operation of the operational amplifier I need at least
+8V and -8V voltages.
I can build a simple voltage multiplier and inverter like shown here:
http://upload.wikimedia.org/wikipedia/en/thumb/b/ba/Stacked_Villard_cascade.svg/400px-Stacked_Villard_cascade.svg.png
using the 6-CMOS inverter chip as an oscillator and a source of alternating
voltage.
However antoher idea is to use something cheap and standard like MAX232.
Has anybody tried to use this chip just as a voltage converter?
Unfortunately I can't find the output characteristics for V+ and V- pins.
Maybe I'll need also additional voltage regulator to improve the quality of
this power supply voltage (or maybe simple RC filter will be sufficient...).
Has anybody tried to do it?
--
TIA & Regards,
WZab
http://www.ise.pw.edu.pl/~wzab/gps_logger - Open Sourse GPS logger with voice recording