AN2450 datasheet(31/35 Pages) STMICROELECTRONICS

31 / 35 page

DocID12784 Rev 6

31/35

AN2450

Electrical test results

has a good margin for ZVS operation, providing good efficiency, while the almost sinusoidal

current waveform just allows for an extremely low EMI generation.

Figure 14. Resonant circuit primary side waveforms at nominal dc input voltage and

full load

Figure 15 and Figure 16 show the same waveforms as Figure 14 with both outputs lightly

loaded (50 mA each) and not loaded, respectively. These graphs demonstrate the ability of

the converter to operate down to zero load, with the output voltages still within regulation

limits (as can be seen looking at Ch3 waveform, representing the +200 V output voltage).

The resonant tank current, in this load condition, assumes, obviously, an almost triangular

shape and represents the magnetizing current flowing into the transformer primary side.

Figure 15. Resonant circuit primary side waveforms at nominal dc input voltage and

light load

Ch1: half-bridge square voltage

Ch2: resonant tank current

Ch3: +200 V output voltage

Ch1: half-bridge square voltage

Ch2: resonant tank current

Ch3: +200 V output voltage

AN2450 Fiches technique(PDF) 31 Page - STMicroelectronics