KA3511DS

November 2,1999 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 protection, 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 respectively. Precision reference section The reference voltage trimmed to ±2% (4.9V