Rev C, November 1999

November 2,1999

1

AN4003

PC POWER SUPPLY DESIGN WITH KA3511

Sang-Tae Im

1. GENERAL DESCRIPTION

The KA3511 is a fixed-frequency improved-performance pulse-width modulation control circuit with

complete housekeeping circuitry for use in the secondary side of SMPS (Switched mode power

supply). It contains various functions, which are precision voltage reference, over voltage protec-

tion, under voltage protection, remote on/off control, power good signal generator and etc.

OVP (Over voltage protection) section

It has OVP functions for +3.3V,+5V,+12V and PT outputs. The circuit is made up of a comparator

with four detecting inputs and without hysteresis voltage. Especially, PT (Pin16) is prepared for an

extra OVP input or another protection signal.

UVP (Under voltage protection) section

It also has UVP functions for +3.3V, +5V, +12V outputs. The block is made up of a comparator with

three detecting inputs and without hysteresis voltage.

Remote on/off section

Remote on/off section is used to control SMPS externally. If a high signal is supplied to the remote

on/off input, PWM signal becomes a high state and all secondary outputs are grounded. The

remote on/off signal is transferred with some on-delay and off-delay time of 8ms, 24ms respec-

tively.

Precision reference section

The reference voltage trimmed to ±2% (4.9V<Vref<5.1V)

PG (Power good signal generator) section

Power good signal generator is to monitor the voltage level of power supply for safe operation of a

microprocessor.

KA3511 requires few external components to accomplish a complete housekeeping circuits for

SMPS. The KA3511 is available in a 22-pin dual in-line package.