AN3105

Functional check

Doc ID 16774 Rev 2

11/30

4

Functional check

4.1

PFC circuit

On the lefthand side of Figure 7, some waveforms relevant to the PFC stage have been

captured; the envelope of CS pin (#4) waveforms of the L6562AT is in phase with the MULT

pin (3#) and has the same sinusoidal shape, demonstrating the correct functioning of the

PFC stage. It is also possible to measure the peak-to-peak value of voltage ripple over

imposed to the PFC output voltage; this is due to the low value of the PFC output capacitors.

On the righthand side of Figure 7 the details of some waveforms at switching frequency are

given.

Figure 7.

EVL130W-SL-EU demonstration board: PFC stage and L6562AT waveforms at 230 V -

50 Hz - full load – detail

4.2

Half-bridge resonant LLC circuit

Some waveforms relevant to the resonant stage during steady-state operation are given in

the following pages. The resonant stage switching frequency is about 100 kHz, in order to

have a good trade off between transformer losses and dimensions.

The LLC converter has been designed to operate at nominal voltage and full load at the

resonance frequency, but due to the PFC output voltage ripple at twice the mains frequency

it is driven slightly above and below the resonant tank frequency, according to the

instantaneous value of PFC output voltage.

In Figure 8 (on the lefthand side) some waveforms relevant to the resonant stage ZVS

operation are shown; it is possible to see that both MOSFETs are turned on when resonant

current is flowing through their body diodes and therefore drain-source voltage is almost

zero, achieving good efficiency because the turn-on losses are negligible. The HB MOSFET

voltage de-rating and low operating temperature allow the board MTBF to be increased.

The current flowing in the resonant tank is sinusoidal; in Figure 8 it is possible to appreciate

a slight asymmetry of operating modes by each half portion of the sinewave; half cycle is

working at resonant frequency while the other is working above the resonant frequency. This

CH3: CS

CH1: Vdrain_Q2

CH4: MULT

CH3: CS

CH4: ZCD