3 Cross Regulation and Standby

AN2242

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duration of 1 second - but it cannot be delivered significantly longer because, from the thermal

point of view, the circuit can manage the full load only with the required reliability. The board

has been designed to power a digital decoder equipped with a hard disk drive but it can be

used even for powering a Set-Top box without the Hard disk drive. The measurements shown

in Table 4. are relevant to a load condition typical of a satellite Set-Top box. The 12V and 5V

loads have been reduced with respect to the previous measurements.

Table 4.

Output Voltage Measurement at Reduced, W/O HDD

At minimum load the power supply is still capable of keeping the output voltages regulated

within the specification, as indicated by the measurements in Table 5. Additionally, the auxiliary

voltage has been measured too: note that the voltage powering the IC has a good margin with

respect to the L6668 turn-off voltage.

Table 5.

Output Voltage Measurement at Minimum Load

at 115Vac - 60Hz

at 230Vac - 50Hz

Voltage [V]

Current [A]

Deviation

Voltage [V] Current [A]

Deviation

11.86

1.1

-1.17%

OK

11.76

1.1

-2.00%

OK

1.79

1.7

-0.56%

OK

1.81

1.7

0.56%

OK

4.85

1.8

-3.00%

OK

4.9

1.8

-2.00%

OK

3.27

0.5

-0.91%

OK

3.26

0.5

-1.21%

OK

Pout=

26.45

W

Pout=

26.46

W

at 115Vac - 60Hz

at 230Vac - 50Hz

Voltage [V]

Current [A]

Deviation

Voltage [V]

Current [A]

Deviation

11.72

0.05

-2.33%

OK

11.65

0.05

-2.92%

OK

1.80

0.2

0.00%

OK

1.80

0.2

0.00%

OK

4.77

0.3

-4.600%

OK

4.78

0.3

-4.40%

OK

3.35

0.03

1.52%

OK

3.34

0.03

1.21%

OK

Vin= 115Vac

lin= 0.48Arms

Pin= 33.1W

EFF.= 79.9%

Vin= 230Vac

lin= 0.29Arms

Pin= 33.4W

EFF.= 79.2%

Pout=26.45W

Pout=26.45W

Vin= 115Vac

lin= 0.082Arms

Pin= 3.6W

Vaux=1.5V

EFF.= 68.8%

Vin= 230Vac

lin= 0.05Arms

Pin= 4.2W

Vaux=11.4V

EFF.= 59.0%

Pout=2.48W

Pout=2.48W