AN3011 datasheet(18/37 Pages) STMICROELECTRONICS

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Efficiency

AN3011

18/37

Doc ID 16043 Rev 1

3.1

Light load performance

3.1.1

No-load condition

The input power of the converter was measured in no-load condition, with brown-out

protection disabled (see relevant section) and brown-out protection enabled for different

applied input voltages (see Table 10). The converter in no-load condition always works in

burst mode so that the average switching frequency is strongly reduced. The average

switching frequency values were also measured. The presence of the resistor dividers (R16,

R17 and R18, see schematic of Figure 2) to sense the flyback input voltage, when brown-

out protection is enabled, does not affect the average switching frequency, but obviously

affects the input power due to the power dissipated in the resistor divider itself.

In the ENERGY STAR program version, the power consumption of the power supply when it

is no-loaded is also considered. The compliance criteria is shown in Table 11:

The performance of the demonstration board is far better then required, but it is worth noting

that often the AC/DC adapter or battery charger manufacturer have stricter requirements

regarding no-load consumption, compared to ENERGY STAR requirements, due also to

other standards or recommendations which they want to be compliant with. In cases where

the converter is used as the standby power supply for LCD TVs, PDPs or other applications,

the line filter is often the big line filter of the main power supply which heavily contributes to

the standby consumption, even though the power needed to the auxiliary power supply is

very low.

The ENERGY STAR program does not have other requirements regarding light-load

performance, however the input power and efficiency of the demonstration board, also in

other low load cases, is given in order to supply more complete information.

Table 10.

No-load input power

Vin AC (VRMS)

Pin (mW)

(BR enabled)

Pin (mW)

(No BR)

fSW_AVG (kHz)

19.20

16.80

1.0816

115

22.90

17.50

0.9706

132

25.00

18.60

0.9139

175

33.00

23.00

0.7552

230

48.00

29.00

0.6923

265

62.00

37.00

0.6561

Table 11.

Energy consumption criteria for no-load

Nameplate output power (Pno)

Maximum power in no-load for AC/DC

EPS

0 to = 50 W

< 0.3 W

> 50 watts < 250 W

< 0.5 W

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