Functional check

AN3172

14/31

Doc ID 17230 Rev 1

4

Functional check

The following are some waveforms relevant to the resonant stage during steady-state

operation. The selected switching frequency is about 100 kHz, in order to have a good trade

off between transformer losses and dimensions. The converter operates above the

resonance frequency. Figure 8 shows the resonant ZVS operation. It is worth noting that

both MOSFETs are turned on when resonant current is flowing through their body diodes

and drain-source voltage is zero.

In Figure 9 typical waveforms relevant to the secondary side are represented; it is worth

noting that the rectifiers reverse the working voltage and the current flowing through them.

The waveforms during the start at 90 Vac and full load are shown in Figure 10. It is possible

to note the sequence of the two stages; at power-on the L6563H and L6599A Vcc voltages

increase up to the turn-on thresholds of the two ICs. The PFC starts and its output voltage

increases from the mains rectified voltage to its nominal value. In the meantime the L6599A

is kept inactive by the LINE pin (#7) until the PFC voltage reaches the set threshold. Then

the resonant starts operating and the output voltage reaches the nominal level.

Figure 7.

Resonant stage waveforms at 115 V

- 60 Hz - full load

Figure 8.

Resonant stage waveforms at 230 V

- 50 Hz - full load

CH1: HB voltage

CH2: CF pin voltage

CH1: HB voltage

CH2: HV FET gate

CH3: Vcc

CH4: Res. tank current CH3: LV FET gate

CH4: Res. tank current