Introduction to Op-Amps - Part 3
Op-Amp circuits can be designed using low power chips that greatly improve the life of batteries. Choosing larger resistor values when you work out ratios for gains can also reduce current flow. Its hard to know which is the best choice without building it first, and sometimes you find that the power requirements are higher than you want. You can always use rechargable batteries (NiCad and NiMh cost a lot more, but they can be recharged hundreds of times).
You really need at least 6 volts (+ 3 Volts and - 3 volts) to use an Op-Amp at all. If using 1 1/2 volt Alkaline batteries, this would equate to 2 batteries for the + supply and 2 batteries for the - supply. You could also use a single 9 volt battery, with a simple voltage divider to simulate + 4.5 volts and - 4.5 volts. For battery only power supplies, I prefer two 9 volt batteries, because it gives the circuit more potential life as the batteries start going dead.
The multi-battery solutions require a DPST (Double Pole, Single Throw) switch to disable the batteries when not in use. This is more expensive and in general more trouble than many people want. Later, if you decide to use a battery eliminator (AC Power), you'll need 2 battery eliminators.
In general, you'll usually find something like 1 Battery Power Supply the most commonly used method with battery powered equipment. With it, you can easily build in a battery eliminator jack.
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