HomeThe Bluewater BlogAA battery power

Many devices are battery powered, and there is a wide range of battery technologies to choose from: Nicad, NiMH, Lithium, Alkali, etc. They all behave differently and have different caviets. We have designed many products to run off battery power. Often the battery is fixed for the product, however sometimes it is desirable to use a standard battery - such as an AA for example. The problem is there is no guaranteeing which AA a user will use. Nominally an AA battery is 1.5v and the current capacity can vary from 600mAh to 3000mAh. Furthermore rechargeable AA batteries are often 1.2v. A fresh Alkali AA battery can read as high as 1.7v. 3.3v is a common voltage for digital electronics, and it is quite tempting to connect up two AA batteries in series to produce 3.0v and assume that is the power supply sorted. Unfortunately, given the range of AA 'voltages' indicated above, and combined with the fact that battery voltage decreases based on load and capacity, this approach is not acceptable. What needs to be done instead in such a system is to have a boost converter to generate the system 3.3v. On a recent design we used a Linear Tech LTC3539. This works over an input range of 700mV to 5v and can provide up to 2A. If the input is above the system rail - as can happen with some fresh AA cells, the converter still regulates the output voltage (albeit not as efficiently). If the system rail is 3.3v, then the batteries will quickly fall beneath this threshold, so the power loss due to this is not great. If such a chip is used to generate a lower voltage rail, then system operating life will suffer more. Using such a chip to generate a 3v3 rail provides maximum battery life for the system and ensures the majority of energy is drawn from any AA cell before the batteries are 'flat'.

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