AN1132 Datasheet, PDF (1/12 Pages) STMicroelectronics – 90W SMPS FOR MONITORS WITH STANDBY FUNCTION

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.
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
Input Voltage Range (V_in)
Mains Frequency (f_L)
Maximum Output Power (P_out)
Horizontal Deflection
Outputs
Video Amplifier
Vertical Deflection
Heater
Switching Frequency in Normal Mode (f_osc)
Switching Frequency in Suspend / OFF mode (fSB)
Target Efficiency (@ Pout =90W, Vin =88 ÷264 Vac) (η)
Maximum Input Power (@ Pout = 0.5 W, Vin =88 ÷ 264 Vac)
88 to 264 Vac
50/60 Hz
90W
V_out = 200V
I_out = 0.325A
Full load ripple = 1%
V_out = 80V
Iout = 0.125A
Full load ripple = 1%
Vout = ±15V
I_out = 0.33A
Full load ripple = 1%
Vout = 6.3V
Iout = 0.8A
Full load ripple = 2%
40kHz
18kHz
> 80%
≤ 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
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