UTCUT2306/UT2306-3.3V/UT2306-5.0V

LINEAR INTEGRATED CIRCUIT

12

QW-R103-029,A

6

LOAD CURRENT(mA)

10

100

5

4

0

1

200

Figure 11. Output Wall Hours vs Load Current.

Note Rapid Fall-Off at Higher Discharge Rates

3

2

1

Figure 11’s graph varies significantly from electrical efficiency plot pictured on the first page of this data sheet.

Why? As more current is drawn from the battery, voltage drop across the cells’ internal impedance increases. This

causes internal power loss (heating), reducing cell terminal voltage. Since the regulator input acts as a negative

resistance, more current is drawn from the battery as the terminal voltage decreases. This positive feedback action

compounds the problem.

Figure 12 shows overall energy conversion efficiency, assuming availability of 6.5WH of battery energy. This

efficiency approximates the electrical efficiency at load current levels from 1mA to 10mA, but drops severely at

load currents above 10mA (load power above 50mW). The moral of the story is this: if your system needs 5V at

more than 40mA to 50mA, consider using a NiCd battery (1/10 the internal impedance) instead of a AA cell alkaline

battery.