LM3524 National Semiconductor, LM3524 Datasheet - Page 10

• Manufacturer Part Number: LM3524
• Description: Regulating Pulse Width Modulator
• Manufacturer: National Semiconductor

www.national.com
Typical Applications
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
(Continued)
FIGURE 11. Boosted Current Polarity Inverter
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10
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
verse biased, and C
ductor L1 will force V
it, D1 will start conducting and the load current will flow
through D1 and L1. The voltage at V
C
through L1 is equal to the nominal DC load current plus
some I
good rule of thumb is to set I
o
filter giving a clean DC output. The current flowing
L
which is due to the changing voltage across it. A
o
A
is charging. When Q1 turns OFF the in-
negative to keep the current flowing in
A
DS008650-15
is at approximately V
LP-P
A
is smoothed by the L1,
40% x I
IN
o
.
and supplied
IN
, D1 is re-