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Author Topic: Split rail power supply using two plug pack power supplies in series?  (Read 833 times)
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Does this work for powering things like split rail op amps?
On paper it looks OK, but I have a nagging doubt in my mind - something to do with being able to source and sink current.

A Google search didn't find anything.
I'm aware of the NE555 charge pump circuit for generating a negative rail when you only have a positive rail, but I'm concerned about noise and stability for use with an instrumentation op-amp.
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That, that is one method of providing +/- rail voltages with a common ground reference.

The charge pump method is also popular.  Popular enough that there are chips designed to do this without resorting to the LM555 method.  (research the ICL7660)

With proper filtration, you should not see an impact in you instrumentation amp.

I'm curious about your design.  You may not need full +/- voltage swing...
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The circuit is a follow on from this topic "Monitoring it's own current draw"
http://arduino.cc/forum/index.php/topic,64870.0.html

I'm measuring the voltage drop across a 0.2 Ohm resistor in series with the positive wire before it goes into the Arduino.
I'm using two 10:1 matched resistive dividers, one on either side of the sense resistor to drop the voltage to about 0.8v.
The differential voltage is about 3mv.
Currently I'm using 3 LM324 op-amps in an instrumentation config to amplify the signal which works very well except for the monster offset which is of the same magnitude as the measured signal. This is of course can be subtracted in software, but I'm using this as a learning experience so I started looking at low offset op-amps then realized that an real instrumentation op-amp works out cheaper, but the cheapest of these require a split rail.

What I'm doing is probably over the top for this particular application, but as I said it's a learning experience.
 

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I assume you have selected something like the INA128 Instrumentation amp.

I have used these with sensors that output 0-5V using a single supply versus split supply.  The limitation is that you may not get results down close to 0V potential is using a single supply... but it sure can be used with a single supply by just tying V- and Ref together on GND.
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