This application note illustrates ways in which QFET power MOSFETs may be used in switched mode power supplies. It describes a 100KHz, 180W simple off-line power supply with three regulated DC voltages.
This document is an application note titled 'A180W, 100KHz Forward Converter Using QFET' published by Fairchild Semiconductor in July 2000. It illustrates the use of QFET power MOSFETs in switched mode power supplies (SMPS) to improve reliability and efficiency. The note details a specific design for a single-ended forward topology power supply.
| Input voltage | 220V AC |
|---|---|
| Output Voltage and current | +5V/20A, +12V/6A, -12V/0.8A |
| Full load efficiency | 75% |
| Switching frequency | 100KHz |
| Output Regulation | 5% |
| MOSFET rating | 800V/7A |
| Core type | EER3542D |
The stated purpose is not to offer an optimum design but to provide some guidelines on using QFETs for switched mode power supplies.
The control circuit is implemented by the use of the current-mode controller IC, KA3842.
An RCD type clamp circuit is used to reset the main transformer and prevent potential saturation problems.