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

Número de pieza

componentes Descripción

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

The average output current mainly depends on the peak current of the main winding. As a rule of thumb, the

average output current can be calculated as

Io 0.29Ip pk

(2)

It can be also noted that the switching frequency varies with the instantaneous line voltage and reaches minimum

value when minimum line voltage reaches its peak value. Ignoring the zero crossing detection delay and voltage drop

on the MOSFET, shunt resistor, and the freeweeling diode, the minimum frequency is given by:

f T 1T

1

VLo(IVin_MVIN 2 V2o)

(3)

L I MIN

on off

(

1

1)

p p pk in_MIN

p p pk V

2V V

in_MIN

o

o

where Ton and Toff are the ON and OFF time of the MOSFET respectively; Lp is the inductance value of the inductor

main winding; Vin-min is the minimum line voltage as specified in the design specification; and Vo is the output

voltage.

Considering the system’s form factor, efficiency, and EMI performance, it is recommended to set minimum

switching frequency to between 80kHz and 100kHz by choosing proper primary inductance value.

8

Line Regulation

The power factor correction scheme described above also indicates that with higher input voltage, the output

current tends to increase due to higher VR pin voltage. Therefore to produce a stable output current (and lumen

output) versus mains voltage variations it is necessary to implement some compensation scheme to achieve

good line regulation.

In this design, the line regulation is achieved by the IC’s integrated foldback correction function as well as the

circuitry formed by R9, C10, D4, and R13. IC’s ZCV pin is able to detect the input voltage level through R12 and

the Vcc winding (T1’s Pin 7 to Pin8), allowing the IC to vary primary current sense voltage limit according to the

input voltage level. This means the primary current will be decreased when the input voltage increases. The

extent of the compensation can be adjusted with varying the value of R12.

Meanwhile C10, together with D4 and the transformer’s auxiliary winding (Pin1 to Pin8) will produce a negative

voltage which is proportional to the rectified input voltage. With a proper value of R9, the peak voltage level at

the base of Q3, and thus VR pin’s voltage, will be regulated against line voltage variation. The circuit formed by

R14, R15 and ZD3 will add a DC offset to the base of Q2 to prevent it from going to a negative voltage. This

offset alters the peak level of VR’s voltage and as a result determines the output current.

Fine tuning of resistance value of R9 is necessary to provide optimum compensation to the line voltage

variation. As a rule of thumb, R9 can be calculated with the following formula:

N

R9 R8 aux

(4)

Np

where Naux and Np are the number of turns of the coupled inductor T1’s auxiliary winding (Pin1 to Pin8) and

main inductor winding (Pin2 to Pin4) respectively.

Application Note

8

Version 1.1, 2012-08-03

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