Longer battery life is important for mobile
phones and other mobile devices. Short of a breakthrough in new battery technology,
the easiest way to make improvements in operating life is to accurately characterize the dynamic
battery current drain of the device and reduce the drain where possible. Batteries
are very non-ideal energy sources. A battery’s internal impedance and other
characteristics interact with the circuit behavior of a mobile device, influencing
its resultant current drain. Accurate current drain measurements are essential
in order to optimize your mobile device’s battery run-time. This screen
shot shows the pulsed current drain and voltage response on a GSM
mobile phone powered by its battery. As can be seen, a battery has substantial
series output impedance, causing its output voltage to drop in direct proportion
to the mobile device’s current drain. Many mobile wireless devices adapt and
adjust accordingly to compensate for the battery’s characteristics.
A general purpose DC power supply strives to be an ideal voltage source with zero output
impedance by using feedback to regulate its output to a fixed voltage setting.
Unlike a battery, its voltage does not drop proportionally with load current. Also,
feedback regulation has finite response time. This leads to transient voltage drops and overshoots during loading and unloading transitions.
This screen shot shows the same measurements made as before using a general purpose DC
power supply in place of the battery. The voltage response is very different and
the resultant current drain ended up being 10% higher than when using the battery.
As you can see, a general purpose DC power supply is not a good emulator of a
battery used in a mobile device. If a transient voltage drop is large enough,
it can even trigger a mobile device’s low battery voltage shutdown mode. In
contrast, programmable DC sources tailored for powering mobile devices have capabilities
for emulating batteries, including: • Extremely fast load transient response
to minimize voltage drops and overshoots, and accurate emulation of a battery’s
dynamic voltage response • Programmable series output resistance
to emulate a battery’s impedance • Current sinking in addition to sourcing, to
emulate a battery’s charging-current characteristics Agilent Technologies has superior tools designed specifically to emulate the battery of a mobile
device. The N6781A Source Measure Unit is tuned for battery drain analysis. When
combined with an Agilent N6705B mainframe and 14585A software, it is a superior solution
for measuring and analyzing battery current drain in devices such as mobile phones.
This screen shot shows the same measurements as before, but this time using the Agilent
N6781A SMU with battery emulation capabilities, in place of the battery. The N6781A’s
series output resistance was set to match the battery’s 150 milli-ohm value. Both the voltage response and resultant current
drain is comparable to that of the actual battery. To summarize, a general purpose DC power supply does not behave like a battery, often providing
very different current drain results. Using a DC source with battery emulation capabilities
helps assure that you achieve more accurate results, comparable to that of a real battery.
For more info, visit the Agilent website at www.agilent.com/find/N6781.