UM0670 datasheet(7/43 Pages) STMICROELECTRONICS

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Design concept

UM0670

7/43

Doc ID 15327 Rev 2

Figure 3 illustrates a high PF boost converter design concept. Two additional features are

implemented in the application and these improvements are shown in the blue segments.

The first improves circuit behavior during startup (see Section 10.1 for a description) and the

second allows the dimming of the LED down to 0%, or no LED brightness (description

provided in Section 10.2).

Figure 4 shows the design concept of a modified buck converter with a dimming function.

The output LED current is adjusted by setting the proper sense resistor size via the jumpers

(to adjust maximum LED current), together with the proper setting of the capacitor used in

the FOT network (adjust minimum LED current). The external PWM generator provides

a PWM signal between 0 and 100% for brightness regulation. This signal is connected

through a diode to the current sense pin and allows control of LED brightness.

Figure 3.

High PF boost converter design concept

AM00413

VOUT = 400 V

Vc = 16 V

Supplying PWM generator with ST7LITEU05

Supplying L6562A in modified BUCK converter

GND

L6562A

Input EMI filter

Proper startup

Allowing

0% dimming

STTH1L06

STP8NM50FP

D104

C110

COMP INV

C107

ZCD

VCC

MULT

VIN = 88 V

to 265 V AC

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