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Design Note

Introduction

The operation of the UC3584Secondary Side Post Regulator can quickly be evaluated in a given sys-tem by using this separate board containing a fully functional auxiliary converter.This controller pro-vides a semiconductor solution for regulating auxil-iary outputs in transformer isolated power supplies where magnetic amplifiers (magamps)where previ-ously used.Circuit operation is synchronized to the main power converter and is based on leading edge modulation.This technique is compatible with both primary side current-mode and voltage-mode controls employed by the main converter.

Circuit Description

As shown in Fig.1,a buck power stage produces the regulated auxiliary output at the AUX OUT con-nector.The input power is provided at V IN and can be connected to a variety of single and double ended buck-derived converters.One such case is shown in Fig.2for a push-pull converter.This power connection is made at the common cathode of the main output node just before the main filter inductor.Connection at this node affords both syn-chronization to the primary controller and power transfer.Note that the oscillator is set at approxi-mately 150kHz to make synchronization to a 170kHz converter possible.To guarantee synchro-nization,the free running oscillator frequency should be set to less than the main frequency by adjusting R11 and C10.

03/99

UDG-98041

1FB BST113

14CT

RT 1112PGND

VREG

BST2VCC 216SYNC COMP 43

CDL Y 65GND SRC 8

OUT VFL T

C10

R11

C11

C14

C15

C16

MAIN IN (TO MAIN OUTPUT 5V)

C17

C13

C12

R10

R13

C1,C2,C3,C4

R12M1

–

VIN

(TO TRANSFORMER

SECONDARY)

AUX OUT (3.3V AUXILIARY

OUTPUT)

–

Figure 1.Evaluation board schematic.UC3584DW Secondary Side Post Regulator Evaluation Board Schematic,and List of Materials By Phil Cooke

Figure 2.Connections between push-pull power stage and UC3584DW evaluation board.

The auxiliary circuit is designed to interface to a 5.0V main output and its output is set to 3.3V at 10W.Other configurations are possible with minor changes to R7,C7,R8,R9,C8,C9and R10.The surface mount design permits the use of the lowest thermal impedance package (UC3584DW)and minimizes required circuit board https://www.wendangku.net/doc/072781620.html,pensa-tion of the auxiliary circuit uses a lead-lag network providing the most flexibility for other designs.Power to the IC (U1)is generated by the boost cir-cuit consisting primarily of L2,D3,C14and an in-ternal boost switch.The boost circuit can be re-placed if desired,by a simple voltage doubler attached to the main transformer secondary wind-ing.

For more complete information, pin descriptions and specifications for the UC3584DW Secondary Side Post Regulator, please refer to the UC3584, UCC3583 and the UCC3808 data sheet or contact your Unitrode Field Applications Engineer.

Reference Designator

Description

Manufacturer

Part Number

C1, C2, C3, C4390μF, 6.3V, R Case Code, Solid Tantalum Sprague, Newark 595D397X06R3R2T C5,C11, C12,C150.1μF, 50V, 1206, X7R, ±10%Xicon, Mouser 140-CC502B104K C6100 pF, 50V, 1206, NPO, ±5%Xicon, Mouser 140-CC502N101J C74700 pF, 50V, 1206, X7R, ±10%Xicon, Mouser 140-CC502B472K C8120 pF, 50V, 1206, NPO, ±5%Xicon, Mouser 140-CC502N121J C90.01μF, 50V, 1206, X7R, ±10%Xicon, Mouser 140-CC502B103K C10220 pF, 50V, 1206, NPO, ±5%Xicon, Mouser 140-CC502N221J C131000 pF, 50V, 1206, X7R, ±10%Xicon, Mouser 140-CC502B102K C14

10μF, 25V, 7343, Tantalum, ±20%

Kemet, Newark

T491D106M025AS

Table 1.Evaluation board list of materials.

UNITRODE CORPORA TION

7 CONTINENTAL BLVD.? MERRIMACK, NH 03054TEL.(603) 424-2410 ? FAX (603) 424-3460

Reference Designator

Description

Manufacturer

Part Number

C16470μF, 6V, 7343H, Tantalum, ±20%Kemet

T510X477M006AS C17 1.5μF, 25V, Tantalum, ±20%Panasonic,Digikey ECS-H1EX155R D1Schottky, 10A, 45V Central Semiconductor CSHD10-45L D2, D41N4148

Diodes Inc.1N4148D3Schottky, 1.0A, 40V IR

10BQ040L133μH, 3.7A rms, 52m ?Coiltronics UP4-330L233μH, 2.4A rms, 98.9m ?Coiltronics UP2-330M1MOSFET, 60V, 0.10?, 14A IR

IRFR024

4.75k ?, 1206, 1/8W Panasonic,Digikey P4.75KFCT-ND R2, R122k ?, 1206, 1/8W Panasonic,Digikey P2.0KFCT-ND R3, R13243?, 1206, 1/8W Panasonic,Digikey P243FCT-ND R4 3.3?, 1206, 1/8W Panasonic,Digikey P3.3RCT-ND R5 3.57k ?, 1206, 1/8W Panasonic,Digikey P3.57KFCT-ND R61k ?, 1206, 1/8W Panasonic,Digikey P1.0KFCT-ND R713.3k ?, 1206, 1/8W Panasonic,Digikey P13.3KFCT-ND R868.1k ?, 1206, 1/8W Panasonic,Digikey P68.1KFCT-ND R957.6k ?, 1206, 1/8W Panasonic,Digikey P57.6KFCT-ND R1017.8k ?, 1206, 1/8W Panasonic,Digikey P17.8KFCT-ND R11

15k ?, 1206, 1/8W

Panasonic,Digikey P15.0KFCT-ND V IN , AUX OUT,MAIN IN Terminal Board Connectors

RDI/Mouser 506-2SV-02COMP, CT Test Points,SMT

Components Corp.TP-108-02U1

Secondary Side Synchronous Post Regulator

Unitrode

UC3584DW

Table 1.Evaluation board list of materials (continued).

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