Negative Voltage

I have seen quite a few questions on websites with people asking how to get a negative voltage to power opamps and such. Well I’m going to toss up a couple of ways on how to do this.

Batteries
Say you’re building a device that requires a LM741 opamp and want it battery powered. The LM741 needs a negative voltage on pin 4 of the IC. Now you need a minimum voltage for the circuit of say 3 volts or two AA batteries. In this case you would need four AA batteries to get a total of 6 volts. Now you wouldn’t be using the whole 6 volts but only 3 volts. The positive and negative for the positive rail would be two batteries and the negative would be the other two however the polarity would be reversed. This is a type of “Voltage Divider”.
batterydivider
The picture above are four AA batteries. The red lines represent the positive rails while the black and blue represent the ground/negative.

Power Supply – Wallwart type
Same issue but instead battery powered and want to use a wallwart style AC adapter. Lets say you need a total of 6 volts to power the circuit. You can use a 12 volt power supply and use a voltage divider circuit. Basically it consists of two resistors that form a virtual ground so the true ground turns into the negative rail.

Example

There are Voltage Divider calculators all over the net. Just google it and you will find them. Just enter the voltage and resistors and it will calculate the output voltages. You can even use this with batteries as well but you might get terrible battery life.

Dual bench power supply
Before you try this double check and make sure your power supply unit/s have “Floating Output”.
Floating Output is non-earth ground reference, meaning the DC ground does not share the AC ground.
To use this all you do is plug in one power supply into the other power supply. Not positive to positive and negative to negative but a single cable you plug into supply A negative and plug the other end into supply B positive.

Example

I hope this helps.

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