AN2450 datasheet(32/35 Pages) STMICROELECTRONICS

32 / 35 page

Electrical test results

AN2450

32/35

DocID12784 Rev 6

Figure 16. Resonant circuit primary side waveforms at nominal dc input voltage and

no-load

In Figure 17, the Ch1 waveform shows a detail of the half-bridge square voltage (directly

taken across pin 14 and pin 10 of L6599 controller) to highlight the softness of voltage edge,

without abrupt negative voltage spikes that would be generated in presence of large stray

inductance of wiring. The layout is very critical in this respect and needs to be optimized in

order to minimize this effect, which could damage the controller itself.

In Figure 18 and Figure 19, waveforms relevant to the secondary side are represented. The

rectifiers reverse voltage is measured by CH1 (for both +200 V and +75 V outputs) and the

peak-to-peak value is indicated on the right of the graph. Waveform CH2 shows the current

flowing into one of the two output diodes for each output voltage (respectively D6 and D8).

Also this current shape is almost a sine wave, whose average value is one half the output

current.

Figure 17. Resonant circuit primary side waveforms at nominal dc input voltage and

light load

Ch1: half-bridge square voltage

Ch2: resonant tank current

Ch3: +200 V output voltage

Ch1: half-bridge square voltage

Ch2: resonant tank current

Ch3: low-side MOSFET gate

(between pin 14 and 10 of L6599)

drive signal

AN2450 Datasheet(PDF) 32 Page - STMicroelectronics