AN3203 datasheet(5/49 Pages) STMICROELECTRONICS

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AN3203

Main characteristics and circuit description

Doc ID 17402 Rev 2

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Main characteristics and circuit description

Here are the main characteristics of the power supply:

●

Input mains range:

–

Vin: 88 ~ 264 Vrms

–

f: 45 ~ 66 Hz

●

Outputs:

–

+12 Vdc ± 2 % - 13.5 A

–

+5 Vdc ± 2 % - 12 A

–

+3.3 Vdc ± 2 % - 8 A

–

+5 V_SB ± 2 % - 2 A

●

Standby consumption: < 0.2 W

●

Protection:

–

Short-circuit

–Overload

–

Output overvoltage

–

Brownout

●

PCB type and size:

–FR4

–

Double side CU 70 µm

–

148 x 120 mm

●

Safety: according to EN60950

●

EMI: according to EN55022 - class B

The EVL250W-ATX80PL demonstration board is made up of four main blocks, the

schematics are shown in Figure 2, 3, 4, and 5.

The front-end PFC stage is realized using a boost topology working in line modulated fixed

off time (LM-FOT) mode, described in STMicroelectronics’ application notes, AN1792;

Design of Fixed-Off-Time controlled PFC pre-regulators with the L6562 and AN3142;

Solution for designing a 400 W Fixed-Off-Time controlled PFC preregulator with the L6563S

and L6563H. The LM-FOT operation offers the advantage of having CCM operation (with

lower rms current with respect to TM mode) without the need to use a complex and

expensive controller. Therefore, it is possible to use the simple L6563S, enhanced TM PFC

controller, which integrates all the functions and protection, needed to control the stage, and

an interface with the downstream DC-DC converter.

The power stage of the PFC is realized with inductor L4, MOSFET Q1 and Q2, diode D3,

and capacitor C1. The LM-FOT operation is obtained with components D6, R15, C10, R14,

C9, R13, and Q3.

The PFC delivers a stable high voltage bus (+400 V nominal) to the downstream converters

(AHB and flyback) and provides for the reduction of the current harmonics drawn from the

mains, in order to meet the requirements of the European EN61000-3-2 norm and the

Japanese JEITA-MITI norm.

The second stage is an asymmetrical half bridge converter, driven by the L6591, a

STMicroelectronics controller dedicated to this topology. This IC integrates all the functions

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