AN2393 datasheet(14/35 Pages) STMICROELECTRONICS

14 / 35 page

Electrical test results

AN2393

14/35

Thus, it is clear that the proposed architecture is really suitable for power supplies operating

with strong load variation without any problem related to the load regulation.

2.3

Stand-by and no load power consumption

The board is specifically designed for light load and zero load operation, as during Stand-by

or Power-off operation, when no power is requested from the +24 V and +12 V outputs.

Though the resonant converter can operate down to zero load, some tricks are required to

keep very low the input power drawn from the mains when the system is in this load

condition. Thus, when entering this power management mode, the ST-BY signal needs to be

set high (by the microcontroller of the system). This forces the PFC pre-regulator and the

resonant stage to switch off (because the supply voltage of the two control ICs is no longer

present (Figure 4) and only the auxiliary flyback converter continues working just to supply

the microprocessor circuitry.

Table 3 and Table 4 show the measurements of the input power in several light load

conditions at 115 and 230 Vac.

These tables show that at no load the input power is lower than 0.5 W.

Figure 12.

Load transition (0 - 100%) on +24 V

output voltage

Figure 13.

Load transition (0 - 100%) on +12 V

output voltage

Ch1: +24 V output voltage

Ch2: +12 V output current

Ch3: PFC output voltage (400 V)

Ch4: + 24 V output current

Dynamic load +24 V @0-6 A - 12 V @ max load (5 A)

Ch1: +24 V output voltage

Ch2: +12 V output current

Ch3: PFC output voltage (400 V)

Ch4: + 12 V output current

Dynamic load +12 V @0-5 A - 24 V @ max load (6 A)

AN2393 Datasheet(PDF) 14 Page - STMicroelectronics