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122 PRODIGIT
5-6. Constant Power mode application
5.6.1
Battery Evaluation
Primary or secondary batteries are the power source for a wide range of portable
electronics products, such as notebook computers, video cameras and mobile
phones. To ensure long usage times and customer satisfaction the battery pack
should be able to provide a constant power for the longest time possible.
It can be measured that the output voltage of a battery will drop over time (Fig 5-6a).
The rate of voltage decay depends on a number of factors including duty cycle,
chemistry type, battery age and ambient temperature.
So to keep the device powered for the longest possible time the battery must be
able to provide a stable power output regardless of output voltage (Fig 5-6c). In
order to maintain a constant power the output current will need to increase over time
to compensate for the reducing voltage (Fig 5-6b).
Operating the 3270 series electronic load in CP mode is ideal for testing the
characteristics of a battery. This is because as the battery voltage drops the load
current will automatically increase in order to keep the CP setting. By logging sink
values against time the test engineer can also measure the battery's energy
capacity at various discharge rates.
The 3270 series also features an adjustable Load OFF setting. This allows a voltage
level to be set so that the electronic load automatically stops sinking power upon
reaching this preset voltage. This can be used to ensure the battery is not subjected
to a damaging deep discharge.
Along with static operation the load can also be operated dynamically in CP mode.
The dynamic functions allow the ramp, fall and plateau times to be adjusted
between 2 levels of power. This capability means that 'real world' loads can be more
accurately simulated. For example the dynamic mode could be used to test the
performance of a battery that is required to provide power pulses to transmit data
from a radio frequency terminal.
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