Functional check

AN3105

16/30

Doc ID 16774 Rev 2

4.5

Converter startup

On the lefthand side of Figure 12 the converter startup is shown. It is possible to note that at

nominal input voltage the converter begins operation in ~150 ms. This is the time needed to

the PFC output voltage starts increasing. Once the PFC output voltage reaches the enable

level set via the L6599AT LINE pin (~ 430 V), even the LLC stage starts switching and the

LLC transformer auxiliary winding. Details of converter sequencing can be found on the

righthand side of Figure 12.

Figure 12.

Figure 12 shows a correct startup of the board using an active load, with only the capacitors

for the 48 V populating the board. When powering current regulators with LEDs it is possible

that the board may show an incorrect startup, with output voltage going up and down and

the LEDs flashing. As already explained in Section 4.3: Dynamic load operation, the board

needs an additional 40 µF capacitance on the +48 V.

CH1: Q2_Drain CH2: HB voltageCH1: Q2_DrainCH2: HB voltage