AN2485

Test results and significant waveforms

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The Power Factor (PF) and the Total Harmonic Distortion (THD) have been measured too

and the results are reported in Figure 12. and Figure 13. As shown, the PF at full load and

half load remains close to unity throughout the input voltage mains range while it decreases

at high mains range when the circuit is delivering 70 W. THD is low, remaining within 25% at

maximum input voltage.

Efficiency is very good at all load and line conditions. At full load it is always significantly

higher than 90%, making this design suitable for high efficiency power supply.

The measured output voltage variation at different line and load conditions is given in Figure

15. As shown, the voltage is perfectly stable over the input voltage range due to the Voltage

Feed-Forward function embedded in the L6593. Only at 265 Vac and light load, there is a

negligible deviation of 1 V due to the intervention of the burst mode (for the "static OVP")

function.

Figure 12.

Power Factor vs. Vin and load

Figure 13.

THD vs. Vin and load

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

90

100

115

130

180

230

265

PF

400W

200W

70W

0

5

10

15

20

25

30

90

100

115

130

180

230

265

THD [%]

400W

200W

70W

Figure 14.

Efficiency vs. Vin and load

Figure 15.

Static Vout regulation vs. Vin and

load

75%

80%

85%

90%

95%

100%

90

100

115

130

180

230

265

Eff [%]

400W

200W

70W

15W

400

400.5

401

401.5

402

402.5

403

403.5

404

90

100

115

130

180

230

265

400W

200W

70W

15W