Datasheet

LM828
www.ti.com SNOS035D –MARCH 2010–REVISED MAY 2013
CASCADING DEVICES
Cascading the LM828s is an easy way to produce a greater negative voltage (e.g. A two-stage cascade circuit is
shown in Figure 14).
If n is the integer representing the number of devices cascaded, the unloaded output voltage V
out
is (-nV
in
). The
effective output resistance is equal to the weighted sum of each individual device:
R
out
= nR
out_1
+ n/2 R
out_2
+ ... + R
out_n
(5)
This can be seen by first assuming that each device is 100 percent efficient. Since the output voltage is different
on each device the output current is as well. Each cascaded device sees less current at the output than the
previous so the R
OUT
voltage drop is lower in each device added. Note that, the number of n is practically limited
since the increasing of n significantly reduces the efficiency, and increases the output resistance and output
voltage ripple.
Figure 14. Increasing Output Voltage by Cascading Devices
COMBINED DOUBLER AND INVERTER
In Figure 15, 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.
Figure 15. Combined Voltage Doubler and Inverter
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