Page 97 - Lindens Handbook of Batteries

3.16 PRINCIPLES OF OPERATION

FIGURE 3.17 Comparison of flat  and sloping  discharge
curves.

In applications where only a narrow voltage range can be tolerated, the selection of the battery
may be limited to those having a flat discharge profile. An alternative is to use a voltage regulator to
convert the varying output voltage of the battery into a constant output voltage consistent with the
equipment requirements. In this way, the full capacity of the battery can be used, with inefficiency
of the voltage regulator the only energy penalty. Figure 3.18 illustrates the voltage and current pro-
files of the battery and regulator outputs. The input from the battery to the regulator is at a constant
power of 1 W, with the current increasing as the battery voltage drops. With an 84% conversion
efficiency, the output from the regulator is constant at a predetermined 6 V and 140 mA (constant
power = 840 mW).

FIGURE 3.18 Characteristics of a voltage regulator. Battery output—1 W; regular output—840 mW.