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Old 30th January 2004, 05:20 PM   #1
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Default Question on a Voltage Inverter

I found this simple schematic for deriving +V/-V from a V source. The design uses a LM380 audio chip to do the work, it doesn't say how much current the circuit is capable of however. Does anyone know how much current this can supply? If I need more than it is capable of, could I use something like the OPA549 instead to handle more current?
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Old 30th January 2004, 07:07 PM   #2
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Apart from the fact that you have drawn the circuit incorrectly (got the inputs and feedback wrong), that is not a voltage inverter, it is a voltage splitter. Essentially it's just an active potential divider. What you show as a pot should actually just be 2 identical resistors. You will only be able to use these kinds of circuit for line level stuff really. Also, unless you are careful, you can end up with 2 grounds with a few volts between them = bad.

edit: you may not need identical resistors with a LM380.
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Old 30th January 2004, 07:43 PM   #3
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Actually I didn't draw it, I just got if off a website. I will draw one up myself with your corrections in it.

I would be using this to power some Op Amps, I was just wondering how many I could power with it at one time. I will be using quite a few OPA2134's and thought if the LM380 wasn't up to the task maybe the OPA549 would pass enough current. I wasn't planing on making an amp with one.
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Old 30th January 2004, 08:31 PM   #4
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Here is my drawing of it using LM380-8 8 pin dip Op Amp. I think the original was drawn with the 14 pin version. I left in the pot since the author explained it was adjusted so the split voltages were made equal. Once I know the value I could replace it with some resistors. These would be used in a car and would actually get ~13.8V normally resulting in ~6.7V after voltage drop from the Op Amp. Would a different design be better?
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Old 31st January 2004, 05:40 PM   #5
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Your schematic looks the same as that other one to me and is still wrong.

The inverting i/p of the op-amp should be connected to the o/p of the op-amp.

The non-inverting i/p should be connected to the pot wiper.

You could power maybe 2-4 chips with this circuit. You may find in a car you get engine whine problems as you have 0V made by this circuit, which is about 6V above the 0V that the headunit and all other 'commercial' components use. Build it and see is my advice.

In my car I made a -ve rail generator using a 555 timer. See Rod Elliott's website for the details of how you can do it.
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