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AN1599 - APPLICATION NOTE

5.4. STAND-BY OPERATION

The SMPS has been loaded at several light load steps to simulate a stand-by operation.

Table 5: Stand-by operation measures

Figure 4: Power consumption versus output current at light load

5.5. WAVEFORMS

In the following pictures there are some waveforms of the application salient parameters. In figures 5 and

6 there are the drain current and drain voltage during normal operation at full load. As clearly visible the

converter works in discontinuous current mode.

For circuit reliability, the drain voltage and diodes PIV have been checked at maximum input voltage and

full load. As shown in picture 7 the drain voltage reaches the maximum value of 551V, the margin respect

to the BVDSS is 179V, assuring a reliable operation of the VIPer12A. The trace A is the magnification of

trace 1 showing the details of the drain voltage.

In SMPS that foresee the operation with low load, the auxiliary winding that supplies the control is

designed to allow the minimum operating voltage also at light load condition. So, the reverse voltage on

the rectifier due to the winding ratio in this power supply is 114Vpkpk at maximum input voltage. Then the

selected diode supplying the VIPer12A (D5), is a BAV21 with a VRRM=250V.

3.3V

Pout

115Vac

Vout

Iout

Pin

η

[V]

[mA]

[W]

[W]

3.33

20

0.067

0.180

37.0%

3.33

30

0.100

0.225

44.4%

3.33

50

0.167

0.310

53.7%

3.33

80

0.266

0.450

59.2%

3.32

100

0.332

0.540

61.5%

3.3V

Pout

230Vac

Vout

Iout

Pin

η

[V]

[mA]

[W]

[W]

3.33

20

0.067

0.200

33.3%

3.33

30

0.100

0.240

41.6%

3.33

50

0.167

0.340

49.0%

3.33

80

0.266

0.480

55.3%

3.32

100

0.332

0.580

57.2%

Stand by operation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

20

30

50

80

100

Iout [m A]

Vin 115Vac

Vin 230Vac