How do I generate a -5V source from these two sources for the use of an OP AMP (needs a + and -)?

Question

If an input into a circuit board is +5 V and GND, how do I generate a -5V source from these two sources for the use of an OP AMP (needs both a + and - Vdd and Vee)?

Generally I would simply switch the ground and +5 terminals to generate a negative voltage, but I don't know how to do this such that the +5 will still be intact. In the end i need a +5, GND, and -5 supply from what I have available.

Is this even possible?

NOTE: Adding a -5V terminal throughout the board is out of the question.

Answer 1

This is easily done with a switching power supply circuit.  For low power, you would only need a couple of components.

In fact, there are modules that do everything for you.

Texas Instruments has a nice little SIP package that is on 0.1" centers which will fit on most breadboards.

Look at the datasheet:

http://www.ti.com/lit/gpn/dch010505d

or product page (which tells you who has them in stock and where to buy them):

http://focus.ti.com/docs/prod/folders/pr...

The DCH010505 would be ideal for you.  It has an isolated output (meaning  you could switch the ground and +5V output to generate the negative supply).

It can source 200mA of current.

Answer 2

you can use a small switching regulator to generate the -5v.

I'll see what I can find.

Simple low current solution is a 555 oscillator running at 50 kHz from +5, and generating a 5 volt square wave and a few diodes and caps.

A cap in series with the signal, a diode to shunt the positive signals to ground (now you have a 0 to -5v square wave) then a diode and cap to peak detect the square wave to -5v.

Actually you will get -4v at best. If you need something better, you can use a voltage doubler and a -5v regulator.

another solution is a LM2682

http://cache.national.com/ds/LM/LM2682.p...

in a small IC package it takes +5v and generates -10v at 10mA, with a few caps and resistors.

There are other similar parts for higher current.

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