User`s guide

Test Results
© 2008 Microchip Technology Inc. DS70320B-page 103
B.5 EFFICIENCY
When loading the 12V output (VOUT1), the efficiency is approximately 82 percent. If
loading the 3.3V and 5V outputs (V
OUT2 and VOUT3) simultaneously, the efficiency is
approximately 74 percent at 300W output. Efficiency is measured by dividing the output
power by the input power. The power is calculated by multiplying the current (load) by
the output voltage. For example, full load on 12V output will yield 360 Watts (12V * 30A
= 360W).
If using an AC power cable, connect a true RMS multimeter in series with the power
cable to measure the RMS input current, and connect another multimeter in parallel
with the power cable to measure RMS input voltage. To calculate input power, multiply
the input RMS current by the input RMS voltage. To calculate the percent efficiency
divide the output power by the input power and multiply the result by 100.
EXAMPLE B-1:
B.6 INPUT CURRENT TOTAL HARMONIC DISTORTION (ITHD)
Using a Voltech PM100 or similar power meter, measure the ITHD. ITHD is tested at
the following conditions:
•V
IN = 110V @ 60 Hz @ Full Load
•V
IN = 220V @ 50 Hz @ Full Load
The current ITHD measurements of the SMPS AC/DC Reference Design at 110 V
AC is
approximately 4.8% and the ITHD at 220 V
AC is approximately 6%.
B.7 POWER FACTOR
Using a Voltech PM100 or similar power meter, measure the power factor. The power
factor of each reference design is tested at the following:
•V
IN = 110V @ 60 Hz @ Full Load
•V
IN = 220V @ 50 Hz @ Full Load
•V
IN = 110V @ 60 Hz @ No Load
•V
IN = 220V @ 50 Hz @ No Load
The current power factor of the SMPS AC/DC Reference Design at 110V at full load is
.998 and the power factor at 220V at full load is .99.
IOUT1 = 0A @ 12V
I
OUT2 = 56A @ 3.3V
I
OUT3 = 23A @ 5V
V
IN = 110V
I
IN = 3.7A
P
OUT = (VOUT1 * IOUT1) + (VOUT2 * IOUT2) + (VOUT3 * IOUT3)
= (56A * 3.3V) + (23A * 5V)
= 299.8W
P
IN = VIN * IIN
= 407W
Efficiency (%) = P
OUT / PIN
= (299.8 / 407) * 100
= 73.7%