Design Specifications

Table 1 summarises the electrical specification of the application. The complete electrical schematic is

shown in fig. 1 and the bill of material is listed in Table 2.

Table 1. Design Specification

88 to 264 Vac

50/60 Hz

90W

Outputs

Horizontal Deflection

Full load ripple = 1%

Video Amplifier

Full load ripple = 1%

Vertical Deflection

±15V

Full load ripple = 1%

Heater

Full load ripple = 2%

40kHz

18kHz

Target Efficiency (@ Pout =90W, Vin =88

÷264 Vac) (η)

> 80%

Maximum Input Power (@ Pout = 0.5 W, Vin =88

÷ 264 Vac)

≤ 2W

The selected topology is flyback. The operation mode (@ Pout = 90W ) is CCM (Continuous Conduction

Mode) at low mains voltage, DCM (Discontinuous Conduction Mode) at high mains voltage. This design

choice relieves the stress on the power components at low mains voltage, compared with a full DCM so-

lution.

The application will benefit from the features of the L5991 PWM controller in order to minimise the power

drawn from the mains under light load conditions: low start-up and quiescent currents, and Standby

function.

September 2000

®

AN1132

APPLICATION NOTE

90W SMPS FOR MONITORS WITH STANDBY FUNCTION

by Claudio Adragna

Purpose of this note is to provide a brief summary of the specifications and the functionality of the ap-

plication board implementing a 90W multioutput SMPS for monitors, based on the L5991, current

mode PWM controller.

Evaluation results are also presented so as to underline the benefits offered by the L5991 in such a

new generation of SMPS that requires a superior efficiency in standby conditions, aiming at compli-

ance with energy saving standards.

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