Some design considerations associated with portable power design have been discussed, such as light load efficiency, voltage regulation accuracy, the battery impedance impact on the end of discharge voltage, battery discharge efficiency and system stability. A portable device needs a battery as its power source when an AC adapter is not available.
BATTERY OPERATED SYSTEM DESIGN CONSIDERATIONS The topology selection is the first step of a portable power circuit design. It is mainly based on the input and output voltage rating, as shown in Fig. 18. If the input voltage is higher than the output at any time, a Buck converter or LDO is normally the only solution.
A portable device needs a battery as its power source when an AC adapter is not available. The battery plays a very important role in the system performance such as system run-time and system stability. Fig. 1 shows the Li-Ion battery discharge characteristics under different discharge rates.
The typical portable power system includes the mini-micro processor, display, memories, I/O interface, and hard disk, each of which requires a different operating voltage rail. Fig. 3 shows the typical range of battery voltages and system voltages.
These loads require different operating voltages and load currents, and are powered by the rechargeable batteries such as Lithium-ion (Li-Ion) batteries, Nickel Metal Hydride (NiMH) batteries and Silver-Zinc batteries through DC-DC converters.
The prominent battery types that are widely used include lead acid, Ni-MH, Li-ion, and Na-NiCl batteries. The emergence of energy storage devices, such as supercapacitors and ultracapacitors, has further boosted the EV system as they charge quickly and release large amounts of power.