This is an application note that describes the design of a 90W monitor power supply, including input/output parameters, switching frequency, target efficiency and maximum input power.
This document details an application board implementing a 90W multioutput Switched Mode Power Supply (SMPS) designed for monitors. The design utilizes the ST L5991 current mode PWM controller to achieve high efficiency and compliance with energy saving standards. The topology selected is flyback, operating in Continuous Conduction Mode (CCM) at low mains voltage and Discontinuous Conduction Mode (DCM) at high mains voltage.
| Input Voltage Range | 88 to 264 Vac |
|---|---|
| Mains Frequency | 50/60 Hz |
| Maximum Output Power | 90W |
| Switching Frequency Normal Mode | 40kHz |
| Switching Frequency Suspend/OFF mode | 18kHz |
| Target Efficiency | > 80% |
| Maximum Input Power Standby | <2W |
The switching frequency changes to 18 kHz when the monitor enters low-consumption mode.
The L5991 controller automatically recognizes low load conditions and reduces the switching frequency to minimize power drawn from the mains.
The board includes overvoltage (OVP) and overcurrent protection (OCP) functions.