AN4501 datasheet(44/48 Pages) STMICROELECTRONICS

44 / 48 page

Calculation details

AN4501

44/48

DocID026394 Rev 1

Equation 30:

Since

, finally:

8.6

Calculation of the freewheeling diode RMS current

By similarity of the MOSFET (see Figure 22) and diode (see Figure 23) current waveforms:

the diode RMS current can be derived from Equation 30.

The peak current and valley currents are the same. The diode conduct during (1 - D) x T in

a switching cycle, whereas the MOSFET conducts during D x T. Therefore in the case of the

diode, D must be replaced by 1 - D in Equation 30.

Equation 31:

Figure 23. Typical current waveform of the freewheeling diode in CCM

8.7

Calculation of the inductor RMS current

Figure 2 shows that:

iL = iM1 (and (iD = 0)) for 0 < t < DT

M1,RMS

L,PP

----------------------

L,PP

----------------













M1,RMS

L,PP

----------------







OU T

–

-------------

M1,RMS

OU T

–

-------------

------

L,PP

------------





 2







D,RMS

–

()

L,PP

----------------







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