AN2450 datasheet(30/35 Pages) STMICROELECTRONICS

30 / 35 page

Electrical test results

AN2450

30/35

DocID12784 Rev 6

The measurements have been done after 30 minutes of warm-up at maximum load. The

circuit efficiency has been calculated at each load condition and input dc voltage and is

plotted in Figure 13, showing very high values at maximum load level, higher than 96.5%.

Also at light load, at an output power of about 10% of the maximum level, the converter

efficiency is very good, reaching a value better than 88% in the whole DC input voltage

range.

Figure 13. Circuit efficiency versus output power at various input voltages

8.2

Resonant stage operating waveforms

Figure 14 shows some waveforms during steady state operation of the resonant circuit at

nominal dc input voltage and full load. The Ch1 waveform is the half-bridge square voltage

on pin 14 of the L6599, driving the resonant circuit. The trace Ch2 represents the

transformer primary current flowing into the resonant tank. As shown, it is almost sinusoidal,

because the operating frequency (about 123 kHz) is close to the resonance of the leakage

inductance of the transformer and the resonant capacitor (C6). In this condition the circuit

Table 4. Efficiency measurements at Vin = 420Vdc

+200 V

At load (A)

+75 (V)

At load (A)

Pout (W)

Pin (W)

Efficiency %

198.35

1.601

76.57

1.008

394.74

407.45

96.88%

198.20

1.301

76.55

0.808

319.71

329.70

96.97%

197.87

1.001

76.47

0.609

244.64

252.55

96.87%

196.85

0.750

76.20

0.410

178.88

185.13

96.62%

198.01

0.504

76.74

0.198

114.99

119.78

96.00%

198.67

0.151

76.98

0.107

38.24

41.92

91.21%

88.00%

89.00%

90.00%

91.00%

92.00%

93.00%

94.00%

95.00%

96.00%

97.00%

98.00%

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

450.00

Output power (W)

@ 390 Vdc

@ 360 Vdc

@ 420 Vdc

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