Developing and testing battery-powered equipment

摘要

How long your cell phone operates depends entirely on how you use it and the battery's state of charge (SOC). Talk a lot, and it will run for much less time than if you just receive a few text messages, regardless of the SOC. Nevertheless, if you have had an important call dropped because the battery's charge became depleted, you know how critical SOC can be. Designers of phones and other portable electronic equipment go to extreme lengths to save power. But to evaluate a new circuit's performance, they don't use batteries. They need a power source that is much better controlled and that allows them to explore corner cases such as a call being received with a nearly depleted battery. They use special power supplies that simulate an actual battery. For many test applications, this means being able to vary the supply's output resistance as well as voltage. Real batteries have internal resistance that changes as the battery discharges and as it ages. Nickel-based battery chemistry shows a relatively large variation in resistance vs. SOC, but lithium polymer cells have virtually constant resistance. The internal resistance of both types of batteries increases with age.