AN2690

Functional check

13/31

Table 1 gives the power consumption from the mains during no-load operation. Thanks to

the L6566A standby functionalities the input power is always below 280 mW.

As referenced in Table 2, the most important international energy saving program

regulations are given. This chipset is compliant to all regulations, mandatory or voluntary,

applied currently or that will become effective in the near future.

The new regulations and voluntary agreements that are coming require that power supplies

and adapters have high efficiency at not only nominal or maximum load but also at light

load. This last condition is frequently a difficult task to achieve, increasing the complexity of

the control part. As previously explained, thanks to the oscillator structure of the L6566A,

just by adding few external components, a frequency foldback circuit can be implemented.

Thus, reducing switching losses improves the power supply efficiency when it is delivering

an output power in the range of 0,5 to 3 W.

The L6566A switching frequency is set by the current flowing in a resistor connected

between the OSC pin and ground (R42). During light-load operation Q5 (Figure 12) injects

into R42 a current inversely proportional to the COMP voltage. The voltage on pin OSC is

constant (1 V) so, increasing Q5 current allows decreasing the current supplied by the pin

and, as a consequence, the oscillator frequency. In this way the converter switching losses,

prevailing at light load, are reduced.

Table 1.

Input power at no load vs. mains voltage

Vin [Vrms]

Input power [W]

90

0.100

115

0.110

230

0.218

265

0.275

Table 2.

International energy saving programs regulations at no load

Energy program

Effective date

Maximum admitted

Compliant

EU code of conduct

Jan 2007

300 mW

Yes

Energy star int.

Jan 2008

750 mW

Yes

California energy

commission

Jul 2008

500 mW

Yes

Group for energy-

efficient appliances

Jan 2007

300 mW

Yes