AN4007

Test board: design and evaluation

Doc ID 022455 Rev 2

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Figure 5.

Efficiency vs. output power

1.3

No-load consumption

The input power of the converter was measured in no load condition, with brownout

protection disabled (see relevant

Section 2.4: Brownout protection) and brownout protection

enabled in the entire input voltage range.

The converter in the no load condition works always in burst mode so that the average

switching frequency is reduced. The presence of the brownout resistor divider (R16, R17

and R18, see schematic in

Figure 2) does not affect the average switching frequency but

increases the input power consumption due to the power dissipated across it.

It is worth noting that often, if the converter is used as the standby power supply for LCD

TVs, PDPs or other applications, the EMI line filter often coincides with the main power

supply line filter that heavily contributes to standby consumption even if the power needed

by the auxiliary power supply is very low.

Table 5.

Load

Efficiency

25%

0.75

4.97

3.73

4.9

76.07%

50%

1.5

4.965

7.45

9.61

77.50%

75%

2.25

4.965

11.17

14.45

77.31%

100%

3

4.95

14.85

19.3

76.94%

Average efficiency

76.96%

02

46

8

10

12

14

16

72

73

74

75

76

77

78

79

115 Vac

230 Vac

average @115 Vac

averege @230 Vac

Output power [W]

CoC & DoE limits

AM11344v1