LM1575/LM2575/LM2575HV
PROCEDURE (Adjustable Output Voltage Versions)
4. Catch Diode Selection (D1)
A.
The catch-diode current rating must be at least 1.2 times greater
than the maximum load current. Also, if the power supply design
must withstand a continuous output short, the diode should have a
current rating equal to the maximum current limit of the LM2575.
The most stressful condition for this diode is an overload or shorted
output. See diode selection guide in
B.
The reverse voltage rating of the diode should be at least 1.25
times the maximum input voltage.
5. Input Capacitor (C
IN
)
An aluminum or tantalum electrolytic bypass capacitor located
close to the regulator is needed for stable operation.
EXAMPLE (Adjustable Output Voltage Versions)
4. Catch Diode Selection (D1)
A.
For this example, a 3A current rating is adequate.
B.
Use a 40V MBR340 or 31DQ04 Schottky diode, or any of the
suggested fast-recovery diodes in
5. Input Capacitor (C
IN
)
A 100
μF
aluminum electrolytic capacitor located near the input and
ground pins provides sufficient bypassing.
To further simplify the buck regulator design procedure, National Semiconductor is making available computer design software to
be used with the Simple Switcher line of switching regulators.
Switchers Made Simple
(version 3.3) is available on a (3�½″) diskette
for IBM compatible computers from a National Semiconductor sales office in your area.
www.national.com
16
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