AN4026 datasheet(13/40 Pages) STMICROELECTRONICS

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AN4026

Efficiency measurements

Doc ID 022603 Rev 1

13/40

2.1

Light load operation efficiency

Measurement results are reported inTable 2. As seen, efficiency is better than 50% even for

very light loads such as 500 mW, as requested by the ErP Lot 6 Tier2 regulation for

computers. Such a high light load efficiency makes the board able to meet also the

regulation ENERGY STAR version 5.0 program for computers.

Measurement procedure:

Because the current flowing through the circuit under measurement is relatively small,

the current measurement circuit is connected to the demonstration board side and the

voltage measurement circuit is connected to the AC source side. In this way the current

absorbed by the voltage circuit is not considered in the measured consumption

amount.

During any efficiency measurement, remove any oscilloscope probe from the board.

For any measurement load, apply a warm-up time of 20 minutes by each different load.

Loads have been applied increasing the output power from minimum to maximum.

Because of the input current shape during light load condition, the input power

measurement may be critical or unreliable using a power meter in the usual way. To

overcome the issue, all light measurements have been done by measuring the active

energy consumption of the demonstration board under test and then calculating the

power as the energy divided by the integration time. The integration time has been set

at 36 seconds, as a compromise between a reliable measurement and a reasonable

time measurement time. The energy is measured in mWh, the result in mW is then

simply calculated by dividing the instrument reading (in mWh) by 100. The instrument

used was the Yokogawa WT210 power meter.

Table 2.

Light load efficiency

Test

230 V-50 Hz

115 V-60 Hz

Vout [V]

Iout

[mA]

Pout [W]

Pin [W]

Eff.

[%]

Vout [V]

Iout

[mA]

Pout

[W]

Pin [W]

Eff. [%]

0.125 W

18.79

7.30

0.137

0.342

40.1%

18.79

7.30

0.137

0.335

40.9%

0.25 W

18.79

13.30

0.250

0.47

53.1%

18.79

13.30

0.250

0.470

53.2%

0.5 W

18.79

27.00

0.507

0.760

66.8%

18.79

26.80

0.504

0.776

64.9%

1.0 W

18.79

54.00

1.015

1.335

76.0%

18.79

54.00

1.015

1.378

73.6%

1.5 W

18.79

79.50

1.494

1.876

79.6%

18.79

79.50

1.494

1.954

76.4%

2.0 W

18.79

106.50

2.001

2.446

81.8%

18.79

106.50

2.001

2.556

78.3%

2.5 W

18.79

133.30

2.505

3.030

82.7%

18.79

133.30

2.505

3.148

79.6%

3.0 W

18.79

106.50

3.016

3.598

83.8%

18.79

106.50

3.016

3.734

80.8%

3.5 W

18.79

186.00

3.495

4.138

84.5%

18.79

186.00

3.495

4.283

81.6%

4.0 W

18.79

213.00

4.002

4.708

85.0%

18.79

213.00

4.002

4.860

82.4%

4.5 W

18.79

240.00

4.510

5.269

85.6%

18.79

240.00

4.510

5.430

83.0%

5.0 W

18.79

267.10

5.019

5.832

86.1%

18.79

267.10

5.019

6.007

83.5%

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