AN4026 datasheet(17/40 Pages) STMICROELECTRONICS

17 / 40 page

AN4026

Functional check

Doc ID 022603 Rev 1

17/40

Functional check

The following figures show the waveforms relevant to the resonant stage during steady-state

operation. The working frequency during steady-state operation at rated load 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 9 shows the HB voltage and

resonant tank current with both the half bridge driving signals.

In Figure 10 the rectifiers reverse working voltages are captured: the good margin can be

noted compared with the BV rectifiers, ensuring reliable, long term operation.

A peculiarity of the L6699 is the self-adaptive deadtime, modulated by the internal logic

according to the half bridge node transition time. Figure 11 and Figure 12 show the

waveforms during full load operation. It is possible to note the measurement of the edges

and the relevant deadtime. It can be seen that both MOSFETs are turned on when resonant

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

achieving the MOSFETs zero voltage switching (ZVS) operation at turn-on.

Figure 9.

Resonant stage waveforms at 115 V

- 60 Hz - full load

Figure 10.

Rectifier waveforms at 115 V - 50 Hz

- full load

CH1: HB voltage

CH3: HVG

CH2: LVG

CH4: res. tank current

CH1: HB voltage

CH3: LV FET gate

CH2: HV FET gate

CH4: res. tank current

AN4026 Datasheet(PDF) 17 Page - STMicroelectronics