AN4027 datasheet(18/41 Pages) STMICROELECTRONICS

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Functional check

AN4027

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DocID022604 Rev 3

Functional check

In Figure 10 some waveforms relevant to the resonant stage during steady-state operation

are reported. The selected switching frequency is about 120 kHz, in order to have a good

trade-off between transformer losses and dimensions. The converter operates slightly

above the resonance frequency. Figure 11 shows key signals of the SRK2000A: each

rectifier MOSFET is switched on and off according to its drain-source voltage which, during

conduction time, is the voltage of the current flowing through the MOSFET.

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

according to the half bridge node transition time. This feature allows the maximization of the

transformer magnetizing inductance, therefore obtaining good light load efficiency and also

keeping correct operation by the HB. Figure 12 and Figure 13 show the waveforms during

full load operation. It is possible to note the measurement of the edges and the relevant

deadtime.

Figure 10. Resonant stage waveforms at 115 Vac

- 60 Hz - full load

Figure 11. SRK2000A key signals at 115 Vac - 60

Hz - full load

CH1: HB voltage

CH2: LVG pin voltage

CH3: HVG pin voltage CH4: ISEN pin voltage

AM11403v1

CH1: GD1 pin voltage CH2: DVS1 pin

CH3: GD2 pin voltage CH4: DVS2 pin

AM11404v1

Figure 12. HB transition at full load - rising edge

Figure 13. HB transition at full load - falling

edge

CH1: HB voltage CH2: LVG

CH3: HVG

CH4: ISEN pin voltage

AM11405v1

CH1: HB voltage CH2: LVG

CH3: HVG

CH4: ISEN pin voltage

AM11406v1

AN4027 Datasheet(PDF) 18 Page - STMicroelectronics