Datasheet

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