AN2393 datasheet(13/35 Pages) STMICROELECTRONICS

13 / 35 page

AN2393

Electrical test results

13/35

Waveform CH3 shows the current flowing into one of the two output diodes for each output

voltage (respectively D8A and D10A). Also this current shape is almost a sine wave, whose

average value is one half the output current.

The ripple and noise on the output voltage is shown on CH2. Thanks to the advantages of

the resonant converter, the high frequency noise of the output voltages is less than 50 mV,

while the residual ripple at twice the mains frequency is lower than 75 mV at maximum load

and any line condition, as shown in Figure 11.

Figure 11.

Low frequency (100 Hz) ripple voltage on the output voltages

Figure 12 shows the dynamic behavior of the converter during a load variation from 0 to

100% on one output, with the other output at maximum load. This figure also highlights the

induced effect of this load change on the PFC pre-regulator output voltage (+400 V on Ch3

track). Both the transitions (from 0 to 100% and from 100% to 0) are clean and do not show

any problem for the output voltage regulation.

Figure 9.

Resonant circuit secondary side

waveforms: +24 V output

Figure 10.

Resonant circuit secondary side

waveforms: +12 V output

+24 V output waveforms:

Ch1: +24 V diode reverse voltage

Ch2: high freq. ripple on +24 V output voltage

Ch3: diode D8A current

+12 V output waveforms:

Ch1: +12V diode reverse voltage

Ch2: high freq. ripple on +12 V output voltage

Ch3: diode D10A current

Ch1: 100 Hz ripple voltage on +12 V

Ch2: 100 Hz ripple voltage on +24 V

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