Combined Doubler and Inverter

In Figure 5, the LM828 is used to provide a positive voltage

doubler and a negative voltage converter. Note that the total

current drawn from the two outputs should not exceed 40

mA.

Regulating V

OUT

It is possible to regulate the negative output of the LM828 by

use of a low dropout regulator (such as the LP2980). The

whole converter is depicted in Figure 6. This converter can

give a regulated output from −1.8V to −5.5V by choosing the

proper resistor ratio:

V

where, V

Note that the following conditions must be satisfied simulta-

neously for worst case design:

V

+I

V

+I

DS100137-11

FIGURE 5. Combined Voltage Doubler and Inverter

DS100137-12

FIGURE 6. Combining LM828 with LP2980 to Make a Negative Adjustable Regulator

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