Measurement results

AN4377

10/29

DocID025410 Rev 1

3

Measurement results

3.1

Efficiency

Figure 3. Overall and DC/DC efficiency

Figure 3 shows overall and DC/DC efficiencies for the converter. Overall efficiency includes

all loss from the RJ45 to the 5 V output voltage rail. DC/DC efficiency is a figure of merit of

the converter standalone and typically does not include the losses associated to the PoE

interface section, that are: the RJ45 connector, data transformer, bridges, power

consumption of the I/F of the PM8800A device.

Figure 4. Efficiency input stage

Figure 4 shows the efficiency comparison implementing on the board three different setting

of bridge rectification. No relevant differences have been highlighted using a standard diode

bridge (1 A or 0.5 A). The best efficiency has been captured using a bridge with four discrete

1 A Schottky diodes, reaching even a gain of about 1%.