# Low Power Consumption Negative Power Supply

#### ajm113

Joined Feb 19, 2011
174
Hello I'm experimenting with op amps at the moment, and for this project I plan on using no more then 5v for this project. What I'm trying to accomplish is creating a negative -3 to -5v power supply off of AA or AAA batteries for a op amp. The battery I'm going to use hasn't been decided yet, but I want to go with a popular easy to find battery that can support enough juice for a op amp and a negative power supply.

Since the goal of this project is to make something very power saving, I need to use have a supply of power that won't be eaten up mostly because of the op amp and a 555 timer IC (555 would be the negative power supply) or a circuit.

Could someone recommend me a link and maybe some tips on improving battery life span on a circuit?

What I'm basically making if your wondering is a tiny portable cheap to manufacture audio mixer.

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#### Wendy

Joined Mar 24, 2008
22,138
There fundamentally is no difference between a positive and negative power supply. If a power supply is isolated, as most are, then it is only a matter which lead you connect to ground. This applies for batteries too.

Creating a Virtual Power Supply Ground

Usually a simple resistor divider will suffice.

If you can get by with large resistors your current draw will be very low.

#### SgtWookie

Joined Jul 17, 2007
22,210
The ICL7660 is a standard switched-capacitor voltage doubler/inverter that can be used for creating a negative supply from a positive supply, up to ~10mA current. It approaches 99% efficiency which is pretty difficult to beat, and it requires only a few external components. These ICs are available for under $2 from many authorized distributors. Thread Starter #### ajm113 Joined Feb 19, 2011 174 Thank you bill for the information! Very helpful! Okay well I found this and it looks promising: The thing I'm noticing is that there is a 1.5v drop, which means if I suspect the op amp would just almost have enough power to run properly. The thing I changed is the supply voltage and resistance. 3v supply and 1.5K resistors instead of 4.7K. This method which is cheaper mind you if lets say I wanted to produce ten prototypes it would cost 5 - 6 dollars for the power supply. Plus I would have spare resistors for future production. Now with the Maxim IC now the draw is very low (which is perfect), I would have to spend$40-\$50 dollars just for the power supply to make ten prototypes. Ouch...

Now that IC would be perfect if I wasn't trying to put myself in a corporate engineer's shoes when designing a product from scratch.

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#### SgtWookie

Joined Jul 17, 2007
22,210
If you are going to use the virtual ground, then increase the size of the resistors, and use an opamp as a voltage follower to keep the virtual ground centered.

If you try to just use resistors, your virtual ground will be all over the place, and you will use up your batteries much more quickly.

#### ajm113

Joined Feb 19, 2011
174
Actually... What if I just got a low power cheap duel op amp? One to give me my negative voltage and the other for my mixer? Would a op amp be a little more promising? Cause if I'm going to need a op amp for that SgtWookie, I may as well just use a op amp for my virtual ground if all I would have to spend is .29c each for a op amp.

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#### SgtWookie

Joined Jul 17, 2007
22,210
Try looking for a micropower RRIO opamp. You can use such an opamp in a single supply configuration.

However, you have not explained what your inputs and expected output will be, so you might not be able to use a single supply configuration. If you are dealing with DC levels, then you will need a dual supply.