ECQ-E2224JF(2012) Ver la hoja de datos (PDF) - Infineon Technologies

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Fabricante

ECQ-E2224JF
(Rev.:2012)

Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6

Infineon Technologies 

AN-EVALLED-ICL8002G-B2

Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6

threshold of the TRIAC. When the input voltage is low, ZD1 as well as Q2 will not conduct. Q1’s gate is charged

by Vcc through R6. When Q1 turns on, the current through R5 helps the TRIAC maintain conduction. As input

voltage rises, ZD1 will pass current to trigger Q2. Once Q2 is on, Q1’s gate will discharge, turning off Q1.

Meanwhile TRIAC’s current is high enough for it to remain in conduction due to the increased current drawing

by the buck converter.

7

Single Stage Power Factor Correction

Single stage power factor correction (PFC) allows for a highly efficient, cost effective and compact LED driver.

In this demo board design, PFC is achieved by sensing the input mains voltage (via R8 and R10) and regulating

the peak current of the coupled inductor T1’s main winding (Pin 4 to Pin2) during each switching cycle to be

proportional to the input voltage.

The formula describing the relationship between the peak current and VR pin’s voltage is given by:

I

p pk (t)

VVR (t) VPWM

GR

V1(t) Vbe VPWM

GR

V1(t)

G

(1)

PWM CS

PWM CS

PWM RCS

where Ip-pk(t) is the peak current of the transformer’s primary winding; VVR(t) is the VR pin’s voltage; V1(t) is the

input voltage sensing signal at the base of Q3; Vbe is the transistor Q3’s base to emitter voltage; VPWM is the

IC’s internal offset voltage with typical value of 0.7V, which is compensated by Q3’s Vbe; GPWM is the IC’s

PWM gain; and RCS is the current sense resistor.

The ICL8002G operates the buck converter in quasi-resonant PWM mode, that means, the current of the

inductor’s main winding is in critical conduction mode. The high frequency sawtooth current in the main winding

is filtered by the output capacitor before flowing to the LED load. Meanwhile the high frequency component of

the input current is filtered by LC filters formed by L1, L2, C2, and C5. Input voltage and current waveforms in

half an AC cycle are illustrated in Figure 3.

Rectified input

Voltage

Primary peakcurrent

envelope

Inductor current Average input

current

Figure 3 Voltage and current waveforms in half an AC cycle

As can be noted from Figure 3, the averaged input current is shaped to be approximately sinusoidal and thus

high power factor is achieved, with input current harmonics fulfilling the requirements of EN 61000-3-2 and ANSI

C82.77-2002 standard.

Application Note

7

Version 1.1, 2012-08-03

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