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LM3524D Datasheet - Page 10

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Typical Applications
(Continued)
FIGURE 11 Boosted Current Polarity Inverter
BASIC SWITCHING REGULATOR THEORY
AND APPLICATIONS
The basic circuit of a step-down switching regulator circuit is
shown in Figure 12 along with a practical circuit design us-
ing the LM3524D in Figure 15
FIGURE 12 Basic Step-Down Switching Regulator
The circuit works as follows Q1 is used as a switch which
has ON and OFF times controlled by the pulse width modu-
lator When Q1 is ON power is drawn from V
to the load through L1 V
reverse biased and C
is charging When Q1 turns OFF the
o
inductor L1 will force V
A
ing in it D1 will start conducting and the load current will
flow through D1 and L1 The voltage at V
the L1 C
filter giving a clean DC output The current flow-
o
ing through L1 is equal to the nominal DC load current plus
some
I
which is due to the changing voltage across it A
L
good rule of thumb is to set I
TL H 8650–16
FIGURE 13
10
Design Equations
V
o
R
5k
1
e
b
F
2 5
1
f
j
OSC
R
C
T
T
2 5V
V
IN
o
L1
e
f
(V
V
) I
a
OSC
o
IN
o
I
V
o
o
C
e
o
V
f
(V
V
)
a
o
OSC
o
IN
TL H 8650 – 15
and supplied
IN
is at approximately V
D1 is
A
IN
negative to keep the current flow-
is smoothed by
A
j 40%
I
c
LP-P
o
TL H 8650– 17

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