Regulating coin cell batteries?

[jp1390]

Hello, I have a circuit that consists of three op-amps (TLC2272CN) and one instrumentation amplifier (INA116). For my purposes, I need to use +/- 6 Volt dual supplies to power these devices.

I was considering using two of these batteries, http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P143-ND, back-to-back to give me my supply range, but it occurred to me that I need to regulate these batteries.

I am now not sure what to do. I like the fact that these coin cells are small, but they only have a 165 mAh capacity and I need a regulated +/- 6 V.

I heard about boost converters, but I think they will take up too much room on my board.

I posed the idea of getting two 9 V batteries and two 6 V regulators, but I am not sure if that will be sufficient.

It says that the both amplifiers require 1.5 mA per channel (max) so I figure that gives 165/6 = 27.5 hours of lifetime for the 6 V coin cell batteries. My device will not be on for longer than a couple minutes at a time, so I don't think power consumption is an issue.

So to sum up, should I just go with the 9 V batteries and regulate down to 6 V, or should I go for the coin cells and somehow regulate them?

Thanks again!

 

[KeepItSimpleStupid]

Lithium batteries have a relatively flat discharge curve. That's not true for 9V batteries.

What's the real reason for regulated supplies? Can you use a rail-splitter IC. Some of the reasons for a regulated supply are the output voltage needed. For really tough designs, the rails may be tracking

 

[jp1390]

Oh well, two of my op-amps create an oscillator circuit. The first op-amp is a bistable multivibrator and operates as a square wave going rail-to-rail. The other op-amp is an integrator that makes a triangular wave. The triangular wave's peak voltages need to be +/- 2 V and are dependent on the supply rails. I just thought that they needed to be regulated for this purpose.

 

[KeepItSimpleStupid]

The regulation of the rails has a lot to do with CMRR. The magnitude of the rails has to to with where the OP amp will saturate.
Off the top of my head, i think you can dispense with the regulation. If you have a regulated supply, you should be able to try different power supply rails and even ones that are asymetric.

Gain, for instance, would be 2, no mater what the power supply rails are. Clipping would occur depending on the magnitude of the rail and the internal drop in the OP amp.

 

[jp1390]

The op-amp that I am using saturates at both supply rails when it oscillates. So I take it that I could probably go without regulating these supplies? Makes my life easier, I guess lol.

 

[audioguru]

If you don't regulate the supplies then the output waveform peak voltage will change lower as the battery voltage runs down.

 

[jp1390]

Yeah, I understand that. I was just hopeful that these Lithium coin cells would be able to hold their voltage for low currents (10 - 200 uA). My device will only be on for minutes at a time.

 

[popsik]

i think you can use a resistor to make 9V to 6V

 

[audioguru]

i think you can use a resistor to make 9V to 6V

No, a simple resistor is not a voltage regulator. The output voltage will change when the current changes and when the input voltage changes.