BASIC CIRCUITRY METHOD AND FEATURES

WHITE LED DRIVERS

Designed for driving LEDs in series configuration

High output voltage, high efficiency (over 80%)

This will be explained by using W-52 as an example.

It is composed of a PWM modulator for activating switch

transistor SW and a oscillator which are inside the IC, as

well as current sensor circuitry Current Control and error

amplifier for detecting the current flowing through the LED

and diode Over Voltage Protection for guarding against

excessive voltage.

It operates by setting the LED current (5mA to 40mA) to

signal travels to the PWM modulator so that the current

flowing through the LED connected to the output equalizes

with the set value, and the switching circuitry, comprised of

an external inductor and switch transistor, varies within an

ON/OFF range and regulates the (PWM) output current in

order to provide a constant amount of current. In irregular

circumstances, such as when the output ter minal is open,

a diode guarding against excessive voltage will prevent the

voltage from rising and protect the circuitry.

Vin

C1

L1

1

6

Vin

5

SHDN

SW

D1

C2

3

LED

SOT23 Pin Numbres

Figure 1: W-52 Block Diagram

ILED

ILED=

225xIs

Over Voltage

Protection

(22V)

W-52

1.2MHz

Oscillator

PWM

& Logic

Current

Control

100 mV

225x

GND

2

Current

Sense

Amp

+

+

–

–