參數(shù)資料
型號(hào)： LM2578MWC
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： 0.75 A SWITCHING REGULATOR, 100 kHz SWITCHING FREQ-MAX, UUC
封裝： WAFER
文件頁(yè)數(shù)： 7/24頁(yè)
文件大?。?/td> 1127K
代理商： LM2578MWC
Typical Applications (Continued)
Capacitor C1 sets the oscillator frequency and is selected
from
Figure 1.
Capacitor C2 serves as a compensation capacitor for syn-
chronous operation and a value of 10 to 50 pF should be suf-
ficient for most applications.
A minimum value for an ideal output capacitor C3, could be
calculated as C = I
o xt/V where Io is the load current, t is
the transistor on time (typically 0.4/f
osc),
and
Visthe
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 volt-
age drop and be fast switching. 1N5819 Schottky diodes
work well.
Transformer selection should be picked for an output transis-
tor “on” time of 0.4/f
osc, and a primary inductance high
enough to prevent the output transistor switch from ramping
higher than the transistor’s rating of 750 mA. Pulse Engi-
neering (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 23 was a Pulse Engineering
PE-64287.
DS008711-13
9V
≤ V
in ≤ 15V
R5 = 270
Vo = 12V
C1 = 1820 pF
Io = 100 mA
C2 = 220 F
Vripple = 50 mV
C3 = 20 pF
fosc = 50 kHz
C4 = 0.0022 F
R1 = 110k
L1 = 220 H
R2 = 10k
D1, D2 = 1N5819
R3 = 0.15
Q1 = D44
R4 = 220k
FIGURE 22. Buck-Boost Regulator
DS008711-14
Vin = 5V
R4 = 0.15
Vo ±12V
C1 = 820 pF
Io = ±40 mA
C2 = 10 pF
fosc = 80 kHz
C3 = 220 F
R1 = 10 k
D1, D2, D3 = 1N5819
R2 = 240 k
T1 = PE-64287
R3 = 240 k
FIGURE 23. RS-232 Line Driver Power Supply
15
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