Quick Question on MOSFET power losses

[augustol]

Hi, everyone,

I was reading an "Application Note" from the International Rectifer and studying it yesterday. I like to do a first read along the whatever-I-am-studying and than come back re-reading it paying more attention to finer detail.

So I was re-reading it today and taking a closer look the formulas than I noticed some terms in the power conduction losses that I couldn't identify.

P_cond=(R_DS(on)/R_L).P₀

The P₀ term could be P_O (for power output maybe?) Since the note doesn't explain anything about the formulas, I suppose it's something dumb and basic, but it's new to me.

So, the R_L and P₀ terms are reffering to what?

Here's the link to the Application Note if anyone want to check it (page 6): https://www.infineon.com/dgdl/an-1071.pdf?fileId=5546d462533600a40153559538eb0ff1

[Manul]

R_L should be load resistance and P_O should be output power (power dissipated in R_L).

[magic]

P=I_RMS²·R_DS(on), simple as that.

Your formula works exactly when P_O is the total power output of the PSU and R_L is the combined resistance of the load and MOSFET. Do the math (I²·R) and see yourself. If R_DS(on) is much less than load resistance, then the approximation given above also gets close enough.

[Picuino]

MOSFET power losses and how they affect power-supply efficiency

Edit:
Basic Concepts of Linear Regulator and Switching Mode Power Supplies