AN2690

Test results

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2

Test results

Efficiency measurement

Figure 3 shows the overall efficiency vs. load, measured at different mains voltages. As

shown the efficiency at nominal load (75 W) is better than 86%. This value is significantly

high, especially if we compare this data with similar converters using two stages and the

downstream converter implements a flyback.

Figure 3.

EVL6566A-75WADP overall efficiency measurements vs. load

The diagram shows the efficiency is not monotonic because of the different contribution of

the switching losses: in fact being the circuit operating at fixed frequency and discontinuous

mode, the flyback MOSFET can turn on at any point between the peak and the valley of the

ringing due to the resonance between the magnetizing inductance and the drain

capacitance, depending by the input voltage and the output load. The phenomenon is visible

comparing the drain waveforms in Figure 6 and Figure 7. Because of a different turn-on

voltage provides different commutation losses, if we put in on a diagram the efficiency as a

function of the output load and input voltage we'll find that the efficiency has not a flat trend.

60%

65%

70%

75%

80%

85%

90%

0

10

2030

405060

7080

Pout [W]

230V 50Hz

115V 60Hz