Tool/software:
1. The source of measurement is PAIR45, PAIR78 is DC. I would like to ask why a bridge rectifier is needed later?
2. I understand that VSS is a negative power rail. Specifically, how does the flow of VSS operate and flow back to the bridge rectifier?
3. I understand that the GATE main MOS is a PWM that controls large currents, but I don’t know the specific purpose of the GAT2 MOS. Since S is grounded, what is the actual conduction method?
Hi chen lun weng,
Thanks for your patience.
1. In PoE 802.3 af/at/bt standards, there is no define that PR12 / PR36 (or PR45 / PR78) should be +DC / -DC or -DC / +DC. So there need a pair of rectifiers to correct the +DC and -DC
2. You can check below simplified diagram about return current flow from VSS to rectifiers
3. GATE is for driving a low-side NMOS in the main power loop, GAT2 is for driving a low-side PMOS for active clamp. Details in https://www.ti.com/lit/an/slua535a/slua535a.pdf
Best regards,
Diang
