LM3524DM datasheet(14/29 Pages) TI

14 / 29 page

LM2524D, LM3524D

SNVS766E – JUNE 2009 – REVISED MAY 2013

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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 VIN and supplied to the load through L1; VA is at approximately

VIN, D1 is reverse biased, and Co is charging. When Q1 turns OFF the inductor L1 will force VA 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

VAis smoothed by the L1, Co filter giving a clean DC output. The current flowing through L1 is equal to the

nominal DC load current plus some

ΔIL which is due to the changing voltage across it. A good rule of thumb is to

set ΔILP-P ≃ 40% × Io.

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