LM828 datasheet(7/15 Pages) TI

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LM828

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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 Vout is (-nVin). The

effective output resistance is equal to the weighted sum of each individual device:

Rout = nRout_1 + n/2 Rout_2 + ... + Rout_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 ROUT 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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