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

perature range) without using any trim-pots or precision re-

sistors. Typical line regulation numbers area1mV 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-

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.

DS011987-17

FIGURE 5. Precision 1A Buck Regulator

DS011987-18

FIGURE 6. Negative Input, Negative or Positive Output Flyback Regulator

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