Use of MAX232 as power supply for operational amplifier in 5V powered system?

Question

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: the 6-CMOS inverter chip as an oscillator and a source of alternatingvoltage.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 ofthis power supply voltage (or maybe simple RC filter will be sufficient...).Has anybody tried to do it?-- TIA & Regards,WZab - Open Sourse GPS logger with voicerecording

TTman · Accepted Answer

The max 232 will give you 10 mA max..

wzab · Answer

Thank you very much.Now I have also found it in the "OUTPUT VOLTAGE vs. LOAD CURRENT"chart on the 4th pageof the 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 alsopresent in the output voltage.What is a typical frequency of this clock?--TIA & Regards,WZab

Vladimir Vassilevsky · Answer

Yes, this works. However, it delivers only few milliamps and the output is very noisy.

Look into ADM202 datasheet.

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That depends on your application.

This is a pretty standard trick.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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David Brown · Answer

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.

boB · Answer

I do this.  ST232A powers an LM393 dual comparator that helps thereceiver 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 area bit higher than other RS232 chips.boB

Andrew Smallshaw · Answer

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.

Jim Stewart · Answer

I've done way worse.These days I prefer a TI TPS60403.  Cheapand less noise.

Use of MAX232 as power supply for operational amplifier in 5V powered system?

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