Datasheet

LM2524D, LM3524D
SNVS766E –JUNE 2009–REVISED MAY 2013 www.ti.com
Figure 21. Boosted Current Polarity Inverter
(3)
Basic Switching Regulator Theory and Applications
The basic circuit of a step-down switching regulator circuit is shown in Figure 22, along with a practical circuit
design using the LM3524D in Figure 25.
Figure 22. 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
modulator. When Q1 is ON, power is drawn from V
IN
and supplied to the load through L1; V
A
is at approximately
V
IN
, D1 is reverse biased, and C
o
is charging. When Q1 turns OFF the inductor L1 will force V
A
negative to keep
the current flowing in it, D1 will start conducting and the load current will flow through D1 and L1. The voltage at
V
A
is smoothed by the L1, C
o
filter giving a clean DC output. The current flowing through L1 is equal to the
nominal DC load current plus some ΔI
L
which is due to the changing voltage across it. A good rule of thumb is to
set ΔI
LP-P
≃ 40% × I
o
.
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