LM3578AM datasheet(22/30 Pages) TI

22 / 30 page

LM2578A, LM3578A

SNVS767E – AUGUST 2000 – REVISED APRIL 2013

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A minimum value for an ideal output capacitor C3, could be calculated as C = Io × t/ΔV where Io is the load

current, t is the transistor on time (typically 0.4/fosc), and ΔV is the peak-to-peak output voltage ripple. A larger

output capacitor than this theoretical value should be used since electrolytics have poor high frequency

performance. Experience has shown that a value from 5 to 10 times the calculated value should be used.

For good efficiency, the diodes must have a low forward voltage drop and be fast switching. 1N5819 Schottky

diodes work well.

Transformer selection should be picked for an output transistor “on” time of 0.4/fosc, and a primary inductance

high enough to prevent the output transistor switch from ramping higher than the transistor's rating of 750 mA.

Pulse Engineering (San Diego, Calif.) and Renco Electronics, Inc. (Deer Park, N.Y.) can provide further

assistance in selecting the proper transformer for a specific application need. The transformer used in Figure 36

was a Pulse Engineering PE-64287.

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LM3578AM Datasheet(PDF) 22 Page - Texas Instruments