AN4027 datasheet(6/41 Pages) STMICROELECTRONICS

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Main characteristics and circuit description

AN4027

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DocID022604 Rev 3

Main characteristics and circuit description

The SMPS main features are listed below:

The circuit is made up of two stages: a front-end PFC using the L6563H, an LLC resonant

converter based on the L6699, and the SRK2000A, controlling the SR MOSFETs on the

secondary side. The SR driver and the rectifier MOSFETs are mounted on a daughterboard.

The L6563H is a current mode PFC controller operating in transition mode and implements

a high-voltage startup to power on the converter.

The L6699 integrates all the functions necessary to properly control the resonant converter

with a 50 % fixed duty cycle and working with variable frequency.

The output rectification is managed by the SRK2000A, an SR driver dedicated to LLC

resonant topology.

The PFC stage works as pre-regulator and powers the resonant stage with a constant

voltage of 400 V. The downstream converter operates only if the PFC is on and regulating.

In this way, the resonant stage can be optimized for a narrow input voltage range.

The L6699 LINE pin (pin 7) is dedicated to this function. It is used to prevent the resonant

converter from working with too low input voltage that can cause incorrect Capacitive mode

operation. If the bulk voltage (PFC output) is below 380 V, the resonant startup is not

allowed. The L6699 LINE pin internal comparator has a current hysteresis allowing the turn-

on and turn-off voltage to be independently set. The turn-off threshold has been set to 300 V

to let the resonant stage operate in the case of mains sag and consequent PFC output dip.

The transformer uses the integrated magnetic approach, incorporating the resonant series

inductance. Therefore, no external, additional coil is needed for the resonance. The

transformer configuration chosen for the secondary winding is center tap.

Table 1. Main characteristics and circuit description

Parameter

Value

Input mains range

90 - 264 Vac - frequency 45 to 65 Hz

Output voltage

12 V at 12.5 A continuous operation

Mains harmonics

Meets EN61000-3-2 Class-D and JEITA-MITI Class-D

No load mains consumption

< 0.15 W according to European CoC Tier 2 for external

power supplies

Minimum four points average efficiency in

active mode

> 89% according to European CoC Tier 2 for external

power supplies

Minimum efficiency in active mode at 10 %

load of full rated output current

> 79% according to European CoC Tier 2 for external

power supplies

EMI

Within EN55022 Class-B limits

Safety

Meets EN60950

Dimensions

65 x 154 mm, 28 mm component maximum height

PCB

Double side, 70 µm, FR-4, mixed PTH/SMT

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