LM3411 Datasheet, PDF (9/13 Pages) National Semiconductor (TI) – Precision Secondary Regulator/Driver

Applications Information (Continued)
FIGURE 5. Precision 1A Buck Regulator
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FIGURE 6. Negative Input, Negative or Positive Output Flyback Regulator
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Improved output voltage tolerance and regulation specifica-
tions are possible by combining the LM3411A with one of the
SIMPLE SWITCHER buck regulator IC’s, such as the
LM2574, LM2575, or LM2576. The circuit shown in Figure 5
can provide a 5V, ±0.5% Output (1% over the operating tem-
perature range) without using any trim-pots or precision re-
sistors. Typical line regulation numbers are a 1 mV change
on the output for a 8V–18V change on the input, and load
regulation of 1 mV with a load change from 100 mA–1A.
A DC-DC flyback converter that accepts a negative input
voltage, and delivers either a positive or negative output is
shown in Figure 6. The circuit utilizes a buck regulator (such
as the LM2574, LM2575, or LM2576, depending on how
much output current is needed) operating in a flyback con-
figuration. The LM3411 provides the reference and the re-
quired level shifting circuitry needed to make the circuit work
correctly.
A unique feature of this circuit is the ability to ground either
the high or low side of the output, thus generating either a
negative or a positive output voltage. Although no isolation is
provided, with the addition of an opto-isolator and related
components, this circuit could provide input/output isolation.
Combining a LM3411A-5.0 with a 1A low dropout linear regu-
lator results in a 5V ±0.5% (1% over the operating tempera-
ture range) regulator with excellent regulation specifications,
with no trimming or 1% resistors needed.
An added benefit of this circuit (and also true of many of the
other circuits shown here) is the high-side and low-side re-
mote output voltage sensing feature. Sensing the output
voltage at the load eliminates the voltage drops associated
with wire resistance, thus providing near perfect load regula-
tion.
A 5V, 1A regulator circuit featuring low dropout, very good
regulation specifications, self protection features and allows
output voltage sensing is shown in Figure 7. The regulator
used is a LM2941 adjustable low dropout positive regulator,
which also features an ON/OFF pin to provide a shutdown
feature.
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