Poe Block - Panasonic BB-HCM547A Service Manual

BB-HCM547A
4.8.

PoE Block

[Power receive]
The power supplied from a LAN cable receives voltage (+48 V) via a diode bridge from a RJ-45 connector (CN502) on the IO
Board.
There are 2 types of PoE receiving methods; a type using unused pins (4, 5, 7 and 8 pin) for LAN data transmission and a type
using the mid point of data lines (1, 2, 3 and 6 pin). This product is compatible with both types because it is equipped with 2 lines
(D501 and D502) of diode bridge circuits
The outputs of the 2 diode bridges described above are connected to the same poles and supply the subsequent circuits + and -
powers.
[PD certification circuit]
The voltage obtained from the diode bridges is supplied to the PD control IC (IC501) of PoE.
The PD control IC (IC501) performs the following operations with the applied voltage from the supply side of power.
For applied voltage of 2.8 - 10 V from the supply side, it returns the internal resistance value of PD control IC (IC604) (25 kΩ).
For applied voltage of 15.5 - 20.5 V from the supply side, it returns the current value by the resistor connected to the Pin (5) of
IC501. (This product is resistance value (45.3 Ω) and it is designed with Class 3 specification.)
When 48 V is applied as the certification progresses, it conducts between the Pins (7) and (10).
[Voltage drop section]
When the power of 48V is supplied to the following DC/DC converter section based on the PD authentication, voltage is con-
verted by PD control IC (IC501), output FET (IC502), switching transformer (T501), rectification diode (D517 and D518), and
capacitor (C513), which results in output of +12 V.
[Switching with AC adaptor]
There is a DC jack (CN601), to which an AC adaptor is connected when POE is not used, and +12 V is input from the AC adap-
tor. Switching of +12 V from the PoE circuit is conducted by using diodes (D521 and D519).
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