AN2359 datasheet(6/18 Pages) STMICROELECTRONICS

6 / 18 page

Application example nº 1

AN2359

6/18

Instead, the -12V/-5V solution can be used all those times where it is not possible to change

the auxiliary supply voltage.

Application example nº 1

The first application example is a 3.3W double output Buck-Boost converter. The

specifications are listed in Table 2.

The schematic of the circuit is shown in Figure 1. and the component list is shown in Table 3.

The input voltage can range from 88VAC to 265VAC. The input section consists in a resistor

as a fuse, a single input rectifier diode and an input C-L-C filter. Such a filter provides both

DC voltage stabilization and EMI filtering. The CSN-RSN leg across D1 helps the further

reducing of the conducted emissions.

The regulation feedback is connected to VOUT2 by means of the PNP transistor Q1 and

zener diode DZ2, in order to provide an output voltage with tight regulation range (the output

precision depends on DZ2 tolerance). VOUT1 is obtained thanks to the turns ratio of the

transformer.

The output inductor is wound in a TDK drum ferrite core (SRW0913 type), with an

intermediate tap for VOUT2. The specifications are the following:

●

L1-3 = 420µH;

●

N1-2 = 70 turns;

●

N2-3 = 62 turns.

Optional bleeder resistors, Rb1 and Rb2, can be connected to the outputs in order to improve

the regulation.

In particular, Rb1 has to be chosen in order to avoid the overvoltage on VOUT1 when VOUT2

is full loaded and VOUT1 is in no load condition.

Table 2.

SMPS specifications

Specification

Value

Input voltage range, VIN

88 - 265VAC

Output voltage VOUT1

-12V

Output voltage VOUT2

-5V

Maximum output current IOUT1

150mA

Maximum output current IOUT2

300mA

Maximum output power

3.3W

AN2359 Datasheet(PDF) 6 Page - STMicroelectronics

AN2359 Datasheet(HTML) 6 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL