AN2755

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 shown in Figure 13 and Figure 14. As visible, the PF at full load and half load

remains close to unity throughout the input voltage mains range while, when the circuit is

delivering 70 W, it decreases at high mains range. THD is low, remaining within 30 % at

maximum input voltage.

The 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 shown in

Figure 16. As visible, the voltage is perfectly stable over the input voltage range. Just at 265

Vac and light load, there are negligible deviations of 1 V due to the intervention of the burst

mode (for the "static OVP") function.

Figure 13.

Power factor vs. Vin and load

Figure 14.

THD vs. Vin and load

 

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

80

130

180

230

280

Vin (Vac)

Pout =400W

Pout =200W

Pout =70W

 

0

5

10

15

20

25

30

35

80

130

180

230

280

Vin(Vac)

Pout= 400W

Pout= 200W

Pout= 70W

Figure 15.

Efficiency vs. Vin and load

Figure 16.

Static Vout regulation vs. Vin and

load

397

398

399

400

401

402

403

404

80

130

180

230

280

Vin (Vac)

Pout =400W

Pout =200W

Pout =70W

Pout =15W