MOSFET and MOSFET driver problem

[corliq]

Why this mobo has MOSFET drivers but still use 3 MOSFET per phase? Thanks!

[Wizard]

Re: MOSFET and MOSFET driver problem

Two have same type, while other one is different. That tells me this is totem pole pull/push with coil connected at midpoint of the totem pole. This way this switching regulator can switch very fast instead of waiting for inductor to fall down on it's own due to energy stored in the coil from high to near low. Now, one transistor pulls voltage in on-off while other set off-on transition to yank the voltage down from high to low rapid enough.

This is necessary when you go above 40-50KHz and this is running around 100-250KHz range.

Cheers, Wizard

[gonzo0815]

Re: MOSFET and MOSFET driver problem

From what i have seen, the lower Mosfets are in paralel, to reduce resistance and rreduce heat and looses.
OEM`s may cheap down here and populate only one. This increases heat and drops efficency significantly.
As long as the MOSFET can handle the current, there is no need for an paralel MOSFET to run the circuit.

The input MOSFET is not switched on very long and currents are mutch lower (well at 12v input voltage to the inductor).
So it does not generate much loss in general.