BASIC CIRCUITRY METHOD AND FEATURES
WHITE LED DRIVERS
1. Boost regulator Type [using coil]
L1
D1
Vin
C1
1
C2
SW
Over Voltage
Protection
(22V)
1.2MHz
Oscillator
LED
–
+
PWM
& Logic
3
I
LED
W-52
Current
Sense
+
–
Amp
100 mV
6
5
Vin
Current
Control
I
LED=
225xIs
SHDN
225x
I
S
GND
2
RSET
SOT23 Pin Numbres
RSET
Figure 1: W-52 Block Diagram
■
FEATURES
■ Circuitry structure and operation
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.
OꢀDesigned for driving LEDs in series configuration
OꢀHigh output voltage, high efficiency (over 80%)
It operates by setting the LED current (5mA to 40mA) to
225 times the current flowing through the RSET pin. An error
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.
