Full Bridge SMPS overcurrent sense

[cupoftea]

Hi,
The attached is a Full Bridge SMPS

Pout=500W,
Fsw=250Khz
Vin=275v, Vout = 28v

Which of the Current sense Positions (1,2 or 3) do you think is best for an overcurrent sense implementation?
LTspice and jpeg as attached.

(BTW, the controller is actually UC2825 in the real cct, and is located on the secondary side.)
{The "current mode current sense", (not shown here) is already done via a CST in the primary side bridge}

 

[wwfeldman]

i see no difference between positions 1 and 2
i think position 3 will only show current when the diode conducts, which is likely less than 1/2 the time.

 

[cupoftea]

Thanks, i actually prefer Position 2, but am told position 1 has 3 less diodes....
Position 3 i think is poor as it involves more diode conduction time, and therefore needs more volts_OFF to make the v.dt_OFF at least equal to v.dt_ON.