[SOLVED] Synchronous Buck Low side MOSFET

[emaniac]

Hi

I have seen buck converter circuit with Low side MOSFETs gate grounded (Low side is OFF in all case).

So i guess this circuit switches the upper MOSFET and use the body diode of the MOSFET as the rectifier diode.

How efficient can this buck be?

Can this be called a Synchronous Buck just because it has two MOSFETs in the circuit?

Now I get this doubt, Is that essential to switch the low side MOSFET (Either way the conduction path is via the Body diode)?

Referring to the equation for losses in buck converter, It seems to me like rds(on) has some role in efficiency.

I don't get this reference explanations right.
Please explain.

Thanks

 

[FvM]

What you describe is of course not a synchronous buck converter. The body diode can be expected to show worse performance than a regular rectifier diode, but you should review the transistor specification details.

In some cases, a synchronous buck converter can be mode switched to asynchronous operation to reduce losses at low output currents. Connecting the transistor permanently as diode doesn't seem to make sense at all.