AN2941 datasheet(13/37 Pages) STMICROELECTRONICS

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AN2941

Efficiency measurement

Doc ID 15447 Rev 4

13/37

Efficiency measurement

EPA rev. 2.0 external power supply compliance

Table 1

shows the no-load consumption and the overall efficiency, measured at the nominal

mains voltages. As shown, these values are fully compliant with the EPA rev 2.0 external

power supply limits, requiring an average efficiency higher than 87% for output load

between 25% and 100% of the nominal load and no-load consumption lower than

500 mW.

In particular at no load the power consumption is very low, in fact at 230 Vac,

it is just 136 mW and at 115 Vac it is 83 mW.

EPA rev. 4.0 computers power supply compliance

Different from the previous EPS regulation, the “EPA rev. 4.0 computers” requires a

minimum efficiency higher than 80%, measured at 20%, 50% and 100% of nominal load. In

Table 2

the comparison of the overall efficiency measurements with the “EPA rev. 4.0

computers” requirements is given.

Additionally, the “EPA rev.4.0 computers” document poses specific limitations to the

maximum consumption of computers during standby mode, sleep mode and idle state but

this is not sufficient to deduce the required power supply efficiency because the load applied

during these states is not indicated. This information comes from computer manufacturer

Table 1.

Overall efficiency compared to “EPA rev. 2.0 EPS”

Notes

230 V-50 Hz

115 V-60 Hz

EPA2

Vout

[V]

Iout

[mA]

Pout

[W]

Eff.

Vout

[V]

Iout

[mA]

Pout

[W]

Eff.

No-load consumption

19.08 0.00

0.00

0.136

------

19.09 0.00

0.00

0.083

------

<0.5W

Pass

25% load eff.

19.12

980

18.73 22.37 83.7% 19.10

983

18.76 21.50 87.3% 87.0%

50% load eff.

19.13 1960 37.50 42.87 87.5% 19.11 1963 37.52 42.12 89.1% 87.0%

75% load eff.

19.16 2936 56.23 63.31 88.8% 19.13 2942 56.26 63.33 88.8% 87.0%

100% load eff.

19.15 3917 75.01 84.07 89.2% 19.14 3920 75.00 85.26 88.0% 87.0%

Average active load eff.

87.3%

88.3% 87.0%

Pass

Table 2.

Overall efficiency compared to “EPA rev. 4.0 computers”

Notes

230 V-50 Hz

115 V-60 Hz

EPA4

Vout

[V]

Iout

[mA]

Pout

[W]

Eff.

Vout

[V]

Iout

[mA]

Pout

[W]

Eff.

20% load Eff.

19.12

785

15.02

18.17

82.6%

19.10

785

14.99

17.39

86.2%

80.0%

PASS

50% load Eff.

19.13

1960

37.50

42.87

87.5%

19.11

1963

37.52

42.12

89.1%

80.0%

PASS

100% load Eff.

19.15

3917

75.01

84.07

89.2%

19.14

3920

75.00

85.26

88.0%

80.0%

PASS

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